Back to Part 1 of TS-940 page: Click here









RF BOARD 1: Board Runs very Hot.. 2


TS-930 (and TS-940…) Power amplifier repair.. 4

Alternative replacement for MRF485. 6



Repairing old fluorescent displays (to brighten up dim digits) 12





Service Manual & Serial Numbers.. 15

Identifying When Radio Manufactured.. 17

BULBS.. 20

Sub display bulb: 20

S Meter Display Bulbs. 24







PARTS.. 37



















RF BOARD 1: Board Runs very Hot 

 [Kenwood] ts940s - PCB burning


Tue, 4 Mar 2003 20:06:53 -0600

That is the way they run, very hot. Reflow the solder on them with good

solder and don't worry about it.

Clif Holland,  KA5IPF


Authorized Kenwood and Icom Service  

----- Original Message -----

From: "PY2NFE" <>

To: "Kenwood" <>

Sent: Tuesday, March 04, 2003 7:52 PM

Subject: [Kenwood] ts940s - PCB burning


Hi Gang:

I need a help A TS940S is with a part from the printed plate of circuit - RF unit - blackened, but barely in the region of the transistors Q6, Q7 and Q8

(armored rectangular area).  Already verify everybody the tensions and RF levels and is everything OK, but the transistors are heating more than the

normal one, causing problems in the solder. Soon after it link the radio the transistors (and all the region in return) already are with temperature

above of the normal one Someone has some idea?



Ronaldo Brisolla -  PY2NFE










Editor note: Although about a TS-930 amplifier, this information maybe useful for repair of the TS-940 final amplifier.



repair notes

Power Amplifier


When I purchased my first TS-930S, it had a number of "improvements" that the owner had added. One of his selling points was that he'd pushed the power output to 150W because the "28-volt transistors could handle it." [I bought the radio because it had three Inrad and one Kenwood filters plus the PIEXX board and the service manual, figuring that for $650 I could remove the PIEXX board and the filters even if the radio was junk.] Although I removed almost all of the other modifications, I naively failed to spend 30 seconds to reduce the output power. It wasn't until my PA failed that I learned how fragile the PA in the '930 really was.


When the 28.5-volt power supply fails, it is invariably related the failure of the MRF-485 driver transistors. However, if you have low or no output and a good 28.5-volt power supply, check the mechanical and electrical integrity of the coaxial cables that connect the signal unit to the PA. I got an outstanding deal on a "low output" '930 on eBay only to find it had dirty contacts on the input connector for the PA. Unfortunately, this is rarely the case. Further, the MRF-485 Kenwood used in the TS-930S and TS-940S is a low-hFE grade of the part that often difficult and expensive to obtain. Higher gain parts are readily available although still somewhat more expensive than the NTE-listed substitute, the NTE236.


W6NL claims that he made a successful substitution of the NTE236 for the MRF-485 as well. However, ON7WP/AA9HX makes a rather scathing assessment of the choice suggesting a much cheaper FET. Although I agree that the MRF-485 [and the NTE236] is being pushed very hard, his sounds like a convoluted solution which I believe is neither justified nor necessary. He offers no indication of whether he checked the hFE of the NTE236's he burnt-up before trying the FET. This is a subtle, yet crucial, consideration because I believe that high gain in the driver stage leads to instability, inciting both the power supply and driver failure. Of a handful of NTE236 parts that I ordered from Jameco Electronics, all but one were clustered around a DC hFE value of approximately 80, which is substantially higher than the YELLOW and ORANGE coded MRF-485's [specified by Kenwood] corresponding to a maximum hFE of 52. The remaining part measured at 52, suggesting that Leeson may have been fortunate to have used a lower-gain pair.


KB2LJJ/CT1APV offers some help in his rather complete discussion of mods for the TS-940S, which contains a similar, if not identical, PA to the '930. Apparently a design change to the bias network in the '940 production run allowed the radio to use the higher gain drivers. This change involves increasing the value of resistors in the part of the bias circuit where diodes are thermally-bonded to one of the drivers and the PA heat sink to mitigate thermal run-away. According to this suggestion, I increased the value of R16 to 2.2k Ohms.


After installing the new drivers, replaced the regulator transistor Q6. The bias on the emitters of Q2 and Q3 remained near 0.1 volts. Eventually, I tracked this down to zener diode D5, which I replaced with an NTE5078A. In the process, I also replaced Q9 with an NTE377, which turned-out to be unnecessary. But, I include it for completeness.


According to W6NL and the service manual, I reset the bias on the drivers to 60 mA. I conservatively chose to shoot for the low end of the bias tolerance suggested by the service manual to avoid provoking unnecessary instability. At the suggestion of KB2LJJ, I let the radio transmit in USB mode with no audio input for well over an hour, monitoring the bias current through L7 carefully for changes. I then reset the CW carrier and TUNE carrier to 110 W and 55 W, respectively. Finally, I listened to myself on a second receiver as I sent some CW at 35 wpm into a dummy load. Sounds good. I was able to test the radio in the January 2006 North American QSO Party CW contest for about 8 hours, where it was subjected to high duty-cycle CQing and high SWR on 160 meters. The radio has continued to perform well [as of February 15, 2006] under occaisional contesting and casual operating.

Parts and Suppliers


A list of all the parts I replaced in the PA are in the table below. I purchased my parts from Mouser Electronics and Jameco Electronics. Both of these companies carry nearly the complete NTE line, although Jameco tends to be slightly cheaper. Many larger cities have a local electronics emporium [not the one with the Answers, although they probably can order them] or two that carries NTE/ECG replacement semiconductors or even original replacements. This repair should cost around $35 dollars as I described. You may also elect to obtain original parts at higher cost from RF Parts or East Coast Transistor.


id             part                                        replacement

Q2,Q3    MRF-485LB                         NTE236

Q6          2SC496(Y)                            NTE295

D5           BZ-192                                  NTE5078A

R16         1.2 k-ohm                              2.2 k-ohm


Good luck. I appreciate your feedback, particularly from readers who have actually attempted or completed this repair, either on their own or using my comments.


Update [18 June 2006]: the NTE236 has been discontinued. You may be able to find vendors who still have it; but, prospects are not good.


[c] 2006 ethan miller . k8gu : name[at]




TS-930 (and TS-940…) Power amplifier repair

(or how to replace bipolars by FET’s…)

Revision 2 by Pedro M.J. Wyns ON7WP-AA9HX dd. 20031228

Kenwood made a big mistake by putting two MRF485 transistors rated 25 V DC Vce max in the driver stage of these great rigs running on 28 V. It is still a mystery for me how it ever worked but there is a huge collection of broken TS-930 and TS-940 around this globe waiting for repair. Usually the 28 Volt regulator transistors fail due to heat (use 240 Volts setting instead of 220 V) and these broken series regulators put 36 Volts on the final module. Boom!!!! The powerstage MRF422 survives, as well as the predriver, but the MRF485 goes into smoke after milliseconds with a short circuit between C and B.

Start by replacing the two shorted regulator transistors 2N5885    [....  Editor Note: some un-needed text removed here from original]

Check for 28 Volts.

Don’t try to find spare MRF485 transistors. They are no longer made and the ones you can still find at an indecent price are NOT SUITABLE due to a far too high HFE causing instability and oscillation. The otherwise excellent article by W6NL Dave Leeson suggests using the NTE236 but this ‘ersatz’ one is also having the same low Vce of 25 V DC. Unless you want start by blowing up three pairs of these 15 $ transistors like I did, you better believe me, this is a bad replacement part….

Halleluia….There is a far better AND CHEAPER solution, putting in FET’s instead… I started on my broken rig number one (I collect them J …) by using IRF730’s. IRF710 would be a better choice but no longer available in Europe after Radio Shack closed down. After replacing some other parts I got 100 watts out on all bands from 160-30 meter, but only 50 watts on 20 and QRPp on 10 meter… although better than no output…but not a perfect solution. Boah…

One day (a sleepless night and one bottle of 1998 French wine) later…however, broken rig number two ( J …) was modified using the even cheaper but well available P4NA80 by ST. The lower gate capacity of this 0.25 $ device gave 100 watts on all bands except 80 watts on 10 meter YES !!! (oops, bottle again empty….)

The mod:
start by rotating both bias pots fully CCW. Replace zener D5 by a 1k load resistor. Replace R13 3.9k by a 1k resistor. Take out the (burned?) R9 and R10 both 22r. Take out the ferrite bridge between these two resistors and mount a 8.2 V 400 mW zener between a ground hole from one of both now missing resistors (anode) and the other hole from the now missing bridge (cathode). This zener replaces the original series of D2 and D3 no longer used. Fets don’t require diode heat sensors. Remove both MRF485’s and put the rig back on. Check if you can adjust the driver bias voltage somewhere between 2 and 6 volts approx. If not the Q6 2SC496 is gone (not in my case but could be…) Turn back the bias pot CCW. Now take a quick nip of the freshly opened bottle Bordeaux 1998…

Perhaps you don’t believe me but all feed-through platings ARE BAD !!! Kenwood really messed up things those days… Cure: put a 0.3 mm silver wire through all of them, especially at the two groundings at the former MRF485 emitter place and at the base and collector of the MRF422’s. Put the P4NA80’s in the place of the MRF485’s after bending the gates completely upward and cutting off the middle pin (drain). Solder source to the groundlug (with the wire in it). Solder one end of a 10 ohm resistor in each base connection (both sides of the PCB) of the former MRF485. (all resistors W) The other end is going to the ‘flying’ gate of the P4NA80 preventing oscillation. That’s it… Put an Ammeter in the power amp red wire supply. Initial current during TX with NO DRIVE is 220 mA. Increase the bias of the FET predriver to 100 ma = 320 mA total consumption by adjusting the bias pot VR2 (about 3,7 V gate voltage). Adjust the final bias to 500 mA = 820 mA total consumption by pot VR1.

Finish by readjusting the IF/RF unit VR8 to 110 watts max after setting the current limiter VR10 to 11 amps while slightly overdriving the amp. Close the rig and empty the bottle Bordeaux.

Who ever said technical articles have to be boring, hips….

If this article was valuable to you please write me a short mail to keep me motivated posting these kind of repair tips.

73’s from ‘Radio Guru Number One’ in Europe…

Pedro M.J. Wyns ON7WP-AA9HX
Moutstraat 7
B-2220 Hallaar
Belgium, Europe, World, Milkyway…


More from John E.Cleeve, G3JVC.

It is true, that Motorola USA has ceased production, of the MRF485, and MRF422, so you cannot buy these transistors "off the shelf" from your local electronics outlet, but as I say, they are still available as spare parts for the TS930s and TS940s, from Kenwood Japan.

MRF485 and MRF 422 transistors I have received are marked "Motorola Japan", and any Kenwood dealer, or, authorised Kenwood spares agent, will be able to obtain the driver and PA transistors for clients, via the Kenwood "spares" organisation, and that includes private individuals. 73, John. G3JVC.




Alternative replacement for MRF485

how ZL3BG replaced MRF485 with

2SC2078 + 12 volt regulator  or

2SC1969 + 12 volt regulator











Martin Sole   pulled both EPROM's from his TS-940S and saved the code in Intel hex format. This is for TS-940S firmware version JA4 (That's what it says on the chip)




 The instruction manual for the IF10_ABC holds a lot of useful information: Circuit diagrams installation instructions, and how to computer interface:




The following came from: Mods.DK Article Id  3352.htm


 The TS-940s inside serial interface is not available now so here is a solution.








































Repairing old fluorescent displays (to brighten up dim digits)


From: [mailto:kenwood-] On Behalf Of Philip, KO6BB
Sent: Wednesday, 9 August 2006 9:23 a.m.
To: Kenwood List
Subject: [Kenwood] Perking up old fluorescent displays


Hi All,

Here is a little trick that users of older radios having fluorescent displays (Kenwood, JRC etc.) might be interested in.


Having just completed the 10Hz digit mod to my Kenwood 430 I was left staring at a display that had some digits that were dimmer than others. This set apparently hadn't been used for a LONG TIME as it had a number of problems when it arrived (worst was the bad solder connections on Voltage Regulator).  Anyway, the display looked "funky".  JRC Radios typically suffer from this malady even more than the Kenwood radios do.  Unused digits/segments gradually turn dim, and may be most apparent on the Tens of MHz digit if the owner is primarily a low band operator!


I've seen this on other radios in the past, so I did the usual "trick" that I do in such cases.  I tuned the radio to 28.88888 MHz and left it turned on continuously.  After being on for about 24 hours the display is brighter and COMPLETELY EVEN in brightness across all digits.  I will leave it on for at least another day just to be sure.


Results?  The display now looks very nice indeed.


73 de Phil,  KO6BB









From: Traian Belinas []


the CAR acts for AM and CW only.


For the AM and CW, the balanced modulator is unbalanced also by CAR pot voltage by D89. for the AM and CW it is adjusted by CAR pot, it is not a fixed value voltage.

D97 is an OR gate which supply the unbalancing voltage for CW or AM modes only (the CAR acts for these modes only), switched by the mode voltages at the Q410 and Q408 outs, so by F and D CWG and AMG bias voltages respectively (connector 12, contact 6 and 4). So you may check for the AMG voltage and switching Q408.

When AM mode, Q408 shall supply the TV voltage (from connector 13) to the right side diode of the D97 then to the CAR potentiometer (CV1, CV2 at connector 14), then by D89 to the balanced modulator and so unbalancing it and so introducing the AM carrier for the TX path.

So, check if the Q408 output is switching from near zero to near TV value when changing modes from SSB to Am and follow that voltage trough that path down to the balanced modulator.



D78 and D79 have to be directly biased, i.e. current shall flow through them when AM. This mean they shall have 0,65 aprox voltage drop, anode to cathode. The current shall flow from the +15V line by the R277/R278 voltage divider to R276 - D78 - D79 - R300 chain to GND.


You shall check the voltage at the R277/R278, and all of the R276 D78 D79 R300 parts and the respective trace.






From: Traian Belinas []


Regarding the FM power, did you tried adjusting the VR9 on the IF board, and checking the bias to the balanced modulator D73?

VR9 settle the FM carrier (ie FM output power), as it is adjusting the DC bias/unbalance to the D73 balanced diode ring modulator for FM.


Some of the TS940 VRs are very very touchy.

The power setting VR on the Control board and VR9 FM car are some of these. I am sure you have observed that others have this behaviour.


I have found the 940 as being the most "unstable" radio from all of I had, as the adjustments are very touchy and also need readjustment sometime or from time to time if you want constant trx parameters .







--- In, "Stjepan Nikolic" <snikolic@...> wrote:

Hi all,
Just a quick question. Which CW filter would you recommend:
YK-88C-1 or YG-455C-1.
The price is very similar but I'm not sure about Performances on 40mtrs band where the noise is stronger than, for example, on 15mtrs band.
73's  Stjepan VK3TSN

From: [] On Behalf Of John Rotondi

Sent: Friday, 17 March 2006 10:07 p.m.


Subject: [ts-940] Re: YK-88C-1 or YG-455C-1


Hello Stjepan,


First, please note that the performance of these filters will not be evidenced by different performance on different bands, since these are 'I.F.' (Intermediate Frequency) Crystal Filters. I.F. Stages are used to provide fixed selectivity across wide frequency ranges while rejecting image frequencies. These are selectivity filters- not 'noise filters'- they will not lessen noise within their passband- but by having a reduced passband (over the SSB

2.4KHz passband let's say), they will pass less noise then the wider passband, so the signal-to-noise ratio within the passband will be greater. Please read the ARRL Handbook sections on Receivers for more information about I.F. stages.


The TS-940 has 4 Intermediate Frequency stages, with the capability of inserting filters into both the 8.83MHz, and the 455Khz I.F. Both the filters you ask about provide the same 500Hz bandpass characteristic, and should provide similar results when compared against each other. The YK-88C-1 is used in the 8.83MHz I.F., and the YG-455C-1 in the 455KHz I.F. You can use either one, or both at once to provide a cascade effect in terms of narrowing the response in the upper I.F. prior to the secondary filter, making the rejection of out-of-passband signals even more pronounced- especially helpful if they are strong

signals. You gain selectivity, and rejection of out-of-passband signals. The in-band noise should not be affected (lessened) by having 2 filters in cascade.


Note there is also a YG-455CN-1 250Hz narrow CW filter available for the TS-940, although this may be at greater expense. If noise is the problem, the narrower filter will have a better signal-to-noise ratio by 3dB over the 500Hz filter, assuming the same insertion loss.


I am using the YG-455C-1 by itself with excellent results, especially when used in conjunction with the CW VBT control and Notch Filter (this helps to notch out noise as well as nearby signals)- but I am not heavily working CW, nor do I have excessive noise. If you are heavily into CW, and especially CW contesting, then using both filters, or, better yet, using the YG-455CN-1 250Hz Narrow CW Filter in the 455KHz I.F. would likely provide the

optimum performance.


If noise is your main issue, it might be worth it for you to start with the narrow YG-455CN-1 CW filter- that might be all you'll need. If not, you can always add a second filter in the 8.83MHz I.F.


BTW, use of the RF Attenuator, or backing off on the RF gain control, and using the AGC in 'Fast' mode while in CW, will help lessen noise, if that is the main issue.


The TS-940 is a great radio! Have fun!


I hope this information is helpful.


73 es gd dx


John, WA2OOB






Service Manual & Serial Numbers 

----- Original Message -----

From: "Brian P. Mileshosky" <>

To: <>

Sent: Friday, July 12, 2002 1:11 PM

Subject: [Kenwood] TS-940S Service Manual & Serial Numbers

Hello Everyone,

I have a gentleman who has an original "Revised Edition" Kenwood TS-940S service manual.  However, I do not know what serial numbers it is good for. My TS-940S serial number is 6030606.  Can anyone please comment on if the revised edition is the correct manual to have, given my serial number?

Thanks and 73,

Brian, N5ZGT


Clif" <

Fri, 12 Jul 2002 14:03:51 -0500


Which revision???  

Original Manual, Copyright 1985-2

Revised Manual, Copyright 1985-2/1985-9/1986-2

Revised Manual, Copyright 1985-2/85-9/87-3/87-4/87-10/88-4/88-11/89-08/90-3


That is from 3 different manuals, looks like a sackful of revisions are out there.  

Clif Holland, KA5IPF



Editors note:

Be careful: Digital A Board is double sided: You NEED to be able see colour pictures of the board.

Without colour pictures it is impossible to be able to understand the traces and to work on the board.

Colour pictures of other boards help a lot too.


Revisions identified with Part numbers:

Copyright / Revision

Part Number


















These can be found from time to time on the internet. If you need a service manual, we offer it on a comprehensive CD-ROM, which contains in PDF format, a complete set of TS-940 documents.


- 13 Service Bulletins (above)

-TS-940S Revised Service Manual, 62 pages,

-SO1 service adjustment instructions,

-SP-940 Service Manual,

-VS1 (Voice Synthesiser Unit) Service Manual,

-TS-940S operators manual, 108 pages

-TS-940S Technical Supplement, 48 pages,

- TS-940S promotional brochure 9in full colour),

- IF10B Instruction Manual [internal kit for computer interface control]

- IF232 Instruction Manual [external control unit for computer interface control]

-PC1A Phone Patch  Operator Manual and wiring Diagram,

-YK-88CN manual,

-SWR 2000 Service Manual,

-HS5 Operators manual [headphones]

- SM220 Service Manual, 29 pages [Station Monitor]

-TL 922 Service Manual [1,500 watt linear amplifier]

- TS570 Control Program, fully operational,

-MC-43 operators manual,

-MC-60 operators manual,

-MC-85 operators manual,

-MC-90 operators manual,

- Kenwood miscellaneous connectors schedule,

- All files on this website


If you require the CD cost is $US11.00  plus postage [$US 3.00 to USA, other places will be advised by email].

Payment can be received by Paypal. Please to request delivery.





Identifying When Radio Manufactured 

ZL4AI advice based as much as possible on analysis of facts gathered:


930s                                       reviewed by QST in              Sep 1983

940s serial number 5110330  reviewed by QST in               Feb 1986.

950s serial number 1010616  reviewed by QST in               Jan 1991.

950SDX  serial number          31200011  reviewed by QST in             Dec 1992.



Owners Manual:

940 First Issue has part number

85902 PRINTED IN JAPAN B50-8001-30  K W M X T  (T)

Most likely means the 940 was released in Sep 1985


Service Bulletins:

940 First Bulletin #896 issued 14 Sep 1985

940 Last Bulletin #988 issued 16 Jan 1992


Service Manual

940 1st issue has code 85-2

940 2nd issue has code 85-2

940 Last issue has code 96-11


The first issue may mean the 940 was first circulated by Feb 1985, and the author suspects this was a Japanese Domestic model

Kenwood re-issued service support information until November 1996 which means support for the 940 went on much later than end of production.





From: [] On Behalf Of Charlie Wirth
Sent: Friday, 12 February 2010 10:42 a.m.
Subject: RE: [ts-940] 940 Serial Numbers


I also read somewhere that the serial numbers started with 5xx for the first production run
and then went to 6xx, 7xx, 8xx, 9xx, 0xx, 1xx and finally 2xx.



ZL4AI has personal experience of three 940s

5xx, 7xx, and a 2xx


ZL4AI owns

20500068 which came with hand written records showing

It was purchased on 8 Oct 1990 at the Ham Radio Outlet in San Diego

Inside I see ICs on the control board marked with date codes

8943 to 9025

There were at least there IC with the 9025 date code

9025 is 25th week of  1990, which is 25 June 1990 so these ICs were made about 25 June 1990.

It would seem relatively likely this 940 was made in June 1990 and was number 68 made that month.


Most importantly it proves 940s with a 20 serial number were not made in 1992 and were made in 1990.

It also suggests the 0xx, 1xx and finally 2xx series may have all been made in 1990.



From: [] On Behalf Of Dale
Sent: Saturday, 24 November 2007 5:33 p.m.
Subject: [ts-940] Re: VERY LATE TS-940Sat, 20 mil serial number available.

Hello Kevin, I have a 20 mil serial numbered TS-940SAT also it's # 20700050 but it's not for sale just thought I mention it. Great radio
73, Dale KD5UVV


20700050 is the highest serial number for a 940 ZL4AI has ever seen reference to.


From that it can be concluded the 940 was made as late as July 1990.


At this stage it is concluded the 940 was

Manufactured in some form from approx Feb 1985 to at least July 1990.

Released in the United States from Sep 1985.


Production of the 940 probably stopped in late 1990, because the 950s was released in Jan 1991.

But this is not absolutely certain because ZL4AI has heard that 940s were sold in parallel with the 950 for period.


What is also bizarre is that the alleged X-2 year coding system does not seem to work for 940, because

5xx series 940s were not made in 1983, because the 940 was not released until 1985.


ZL4AI does not know the exact dates, of 940 manufacture and would appreciate being emailed this information.


A well talked about scheme for the 950SDX  is below:

ZL4AI found this system did not work for his TS-940 which was manufactured in 1987 and began with 7

[You will notice this X-2 number year system would identify

950SDX  serial number          31200011  reviewed by QST in             Dec 1992.

as a radio made in Dec 1991, when the 950SDX had not been released.]


It seems that somewhere between 1985 and 1990 Kenwood may have changed the year coding system for the 940.



A good idea is to

Take covers off and look at the IC chips.

Use the date scheme code below [W9IXX email], to confirm when the parts were made.




[Kenwood] TS-950sdx serial number

Bill Martin
Sun, 27 Jan 2002 20:22:07 -0500

Mine is 01100190 so guess that makes it November of 98 - right?
Bill K4SGF
----- Original Message -----
From: NR1DX
Sent: Sunday, January 27, 2002 3:01 PM
Subject: Re: [Kenwood] TS-950sdx serial number
Kenwood serial number decoder
X-2 = last digit of the year
YY = Production Month
ZZZZZ = sequence in production for that month
So Kenny yours would have been the 7th unit to be produced in April of 1998 (the 950SDX wasn't in production in 1988). I'm told that this applies to all Kenwood radios manufactured in at least the last 20 years maybe longer. I wonder what the last official serial number was for the 950SDX? Mine is a 00900014. Anybody out there with a newer one?
At 07:02 PM 1/27/02 +0000, k.d.wilson wrote:
Hi Gang, The serial number of my TS-950sdx is 00400007, can anyone please tell me what year this is?.
>73 de Kenny M1HAM / M5RIG




[Kenwood] Fwd: RE: Feedback from re:serial numbers

Phil Florig

Tue, 09 Mar 2004 17:40:59 -0500

Hi all,

I received the following e-mail reference my inquiry on serial numbers for some of my Kenwood units. This information seems to correlate with the information on the date codes of some of the components.  As you know there are usually Date codes on components.   The common way is to give a 2digit year and 2digit week.

EX:   9340  is 1993 and the 40th week

       8837  is 1988 and the 37th week
As shown below my TS850s ser#60200208 is mfg in 1994. This is right as the component date codes are 9340, 9409, 9350, 9410, and etc. As shown below my TS940s ser#9100162 is mfg in 1988. This is right as the component date codes are 8817, 8825, 8837, and etc. Bottom line is to check as many parts in the rig as you can to see the  general date span. I know that some parts may be older stock and some may have been replaced  but the majority of the date codes should be within a year.  This will hold true for most  medium to high production runs. Hope this helps in some way. Tnx agn guys for all of your inputs on this  reflector and thank you Kenwood for answering my e-mail request so fast.

We do appreciate it.

73    Phil   W9IXX

>Dear Kenwood Customer:



>There is no sequence with our serial numbers. TS-850S s/n 60200208  1994 TS-940S s/n 9100162   1988

>If you need further assistance, please e-mail us again.


>Kenwood Amateur Radio Customer Support



>-----Original Message-----

>From: Philip Florig []

>Sent: Saturday, March 06, 2004 9:22 AM

>To: KCC-Amateur

>Subject: Feedback from



>The question has come up as to the meaning of the serial numbers used. Can you explain the serial number  system to me please.  I have 2-TS830,1-TS850, & 1-TS940. Serial numbers are TS850  60200208 and TS940 is 9100162.  Would like to know date of mfg and any other information.

>Thank you in advance.


>Phil Florig


>Contact Information:

>Email address:

>Call Sign: W9IXX








Sub display bulb:


Editor ZL4AI: 2 Feb 2007:


In my 20 mill 940, both bulbs blew at once

In service manual on page 35 for the LCD, the lamp circuit is shown. The bulbs are specified as 9V at 60 mA = (0.54W )

Editor measured bulbs at 3 mm dia x 7 mm long. 

The mounting hole in the LCD board is 4 mm dia: The hole has plastic bezel around it inside so it cannot be made larger.

Conclusion you will have to use bulbs 3 mm dia or smaller.



Editor measured at his LCD supply volts available at 7.74, (compared with 8 on circuit diagram.)


LEDs? will these work? Advantage: Will increase life to 80,000 hours and reduce power consumption.

Guess will have to experiment to find out what LED works?




Information cross correlating MCD with luminance of a 540 mill watt bulb.

How do I convert between candelas and lumens?

You can’t directly convert since they measure different things. The most useful explanation I’ve found is that lumens measure light output at the source, while candelas measure the light that falls on a surface. As the area of the surface increases, the number of candelas will decrease even as the number of lumens remains constant. So, they measure different things, and there’s no direct conversion. Update: I didn’t find that answer very satisfying either, so I worked out the conversion details and made a conversion calculator for you to use.


Light bulbs and LEDs sold for illumination tend to carry ratings in lumens. Indicator LEDs tend to be rated in candelas.


You can also use this table to get an approximate conversion from candelas to lumens. Find your LED beam width in degrees, and divide the candelas number in your specs by the cd/lm factor listed for that beam angle to get lumens.


beam angle              cd/lm

5                             167.22

10                           41.82

15                           18.60

20                           10.48

25                           6.71

30                           4.67

35                           3.44

40                           2.64

45                           2.09

Re: Lumens / Watts

by Chris Ward on 12/13/05 at 14:17:17


    Lumens and Watts are just photometric and radiometric terms for the same thing: optical power or flux.   The only difference is that photometry (luminous power) takes into account human perception and accounts for the sensitivity of the eye to different colours.   This can make it difficult to convert between the two unless you know the spectra of the bulb.


    By definition,  at the peak sensitivity of the eye (green 555nm) 1 Watt equals 680 lumens.


    It would make the most sense to talk about lumens with a flashligh, because what you really care about is the perceived "brightness", not the true optical power.




    This information can be referenced on pg. 27 of "Optoelectronics", Prentice Hall 1983


so 1 lumen = 1/680 watts



So putting it all together.











Beam Angle

candella / lumen conversion

lumen to mWatt =  1.0/0.68


Cost $NZ

V operating Vo

Current draw I in mA

Resistor Ohms based on R = V [7.74-Vo] / I

Best match resistor
















Green diffused


























Green clear













White clear













White clear













White clear













Green clear













I chose to use the Jaycar 3,500.

What the calculations above illustrate is that the more focus of a narrow beam LED puts out more light in a very small region.

LEDS seem to put out similar light levels, but high powered units intensely focus light into narrow beam.

In our LCD display what we want is diffused light across a wide area. We definitely don want to stare at intense light.

So I filed the lens off the front of the LED and filed all around to make the surface rough. This somewhat increased the diffused light



None of the LEDs will produce 540 m Watts.

The purpose of the resistor is to limit the current draw in the LED to a conservative safe value of 30 m Amps

If I push the current up by 540/491 to 33 m Amps then this can be achieved by a 120 ohm dropping resistor.




White clear












How does it look?

Brighter than the original incandescent bulbs, and more blue in colour.

I will try this for a while. If the blue is too irritating, I will change to the green LEDS with 6,000 mcd.


Power savings: each LED consumes about 130 mWatt, so savings are: 2 x 560 – 2 x 130 = 840 mWatt. This should take a small lad off the AVR board.




Preparing the LED to give diffuse light. Please note that LEDs have a lens at the front. This gives a bright beam of light.

To make his light diffuse:

File it off flat. Use a flat file. and some 220 grit sand paper to roughen the outside.

Do not file off too much, other wise you will expose the anode and cathode connections. Leave these covered by 1 mm of plastic.









The following 5 mm LEDs cannot be used on the LCD, but the date maybe useful when I convert the S meter to LEDs.








Beam Angle

candella / lumen conversion

lumen to mWatt =  1.0/0.68


Cost $NZ

V operating Vo

Current draw I in mA

Resistor Ohms based on R = V [7.74-Vo] / I

Best match resistor































Green diffused










































Green clear














Green clear




























Green clear













































S Meter Display Bulbs


Ham To Ham #13 - October 1996

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108


Lighten up


From George Vaughn WA4VWR comes this tip:


"I've found a local source for the bulbs that illuminate the Kenwood TS-940's sub- display. When one of them went bad in my TS-940S, I removed both and measured the voltage applied to and the current drawn by the single working bulb...12 volts at 75 milliamperes  [Editor note: Kenwood spec is  9V 60 mA, and supply is 8v]  . A trip to the local Radio Shack (reg. trade mark) store resulted in my discovering standard RS replacement bulbs of the exact size and shape (RS Cat. #272-1092), but the RS bulbs draw 15mA less, or 60mA - and they lack the little green "bootie" that the original Kenwood bulbs have. The green "bootie" can be carefully removed from the old bulb, provided it hasn't been "cooked" into place too badly, and with the aid of a touch of clear silicone grease, can be installed on the RS replacement bulb quite easily.


The 15 milliamp difference in current (and light output) is about the same as if one were to put a 47 ohm, 1/2 watt "bulb-life-extender-resistor" in series with the Kenwood bulb, so to me it's perfectly acceptable. The biggest difference is in the price...$1.49 for two of the RS bulbs vs. $4.19 each ($8.38 total) plus $6.00 shipping, for the Kenwood replacements. That's $7.19 per bulb from Kenwood...75 cents per bulb from Radio Shack. Guess which ones I'm using in the future.


What about the TS-940S's 'S-meter' bulbs...does Radio Shack carry a replacement for them? Yes, but this time the difference is more pronounced. The bulbs in the S-meter are 12V at 75mA;





Moderator's note: We've all noticed how difficult it's become to change the pilot lamps inside of most of today's radios? In the old days - when radios and lamps both were a lot bigger - changing a pilot lamp was a pretty straight-foreword, easily accomplished job . The lamps were always mounted in sockets, and usually just a twist of the wrist popped it right out, ready to receive a new one. Not so today...most are now on small wires, soldered in-place and buried deep within the wiring of it's front panel. It usually requires some internal "surgery", so many hams either don't bother changing them at all when they burn out, or they leave the job for when the set has to be disassembled for some other troubleshooting reason. George has offered some well-thought-out advise in his tips from above; here's some more for you to consider.


What follows won't make the task of bulb changing any easier, but it just might double or triple the time between pilot lamp failures. When a lamp does burn out, many probably think first of going back to the manufacturer for a replacement. There's nothing wrong with that idea, especially if it's a very specialized type of bulb. But as George pointed out, it's probably the most expensive and time consuming route to take, especially when there may be a much more cost effective approach. Since Radio Shack stores stock a number of small low voltage lamps, many of which will either fit directly or can be adapted to fit, a bit of "ham innovation" is sometimes needed, as displayed in George's piece. 


Take a look into what Radio Shack calls their 12V micro-lamp, Cat. #272-1092. It may well work as a replacement bulb for LCD displays and other situations where a very small size lamp is in order. Hobby stores also carry what they call "grain-of-wheat" lamps, which are very similar, but be sure to ask about their voltage and current ratings. By the way, using a lamp rated at a higher voltage is fine, as long as it will provide enough brightness once it's installed; in fact, it will last a lot longer than one rated at the nominal voltage. Additionally, if you lower the voltage to a 12V lamp, even by just a couple of volts, you'll increase it's life dramatically. I've seen test curves that prove that the life expectancy of a lamp zooms upward as the voltage across it goes down, and vice versa of course. Putting a resistor in series with each lamp that you replace, will often give you two to three times the life expectency from a given bulb, everything else being equal. 


There are three things to consider before doing this: 1) what value resistor will be needed, 2) what its wattage rating should be and 3) how much loss of light is acceptable? Lowering the voltage to the lamp will decrease its brightness - and shift its color toward the red region - so you'll have to visually judge whether you can accept both of these consequences. 


You can install the lamp, clip-leading a resistor in series with it, then looking at the meter or display under normal room lighting, to see if it's okay for you own particular situation. To arrive at the right resistor values, simply use Ohm's Law, plugging in the correct numbers for your own transceiver's lamp supply: 

Voltage drop desired divided by the lamp's rated current equals the resistance needed.


Voltage drop desired times the lamp's rated current equals the resistor's wattage. 

By way of an example, let's take the Radio Shack #272-1092 lamp that I mentioned before, which has a current rating of 60 mA or .06 Amp. Let's say we'd like to drop the 12 volts feeding the lamp down to 10 volts, or a 2 volt total drop. We plug in the numbers:

2 (volts) divided by .06 (amp) equals 33 ohms


2 (volts) times .06 (amp) equals .12 watt 

Now we know that we'll need a 33 ohm, 1/4 to 1/2 watt resistor in series with each lamp in order to drop the 12 volt lamp supply down to 10 volts. A 1/2 watt resistor will provide a 4 times safety margin for heat dissipation (dissipation ratings for resistors generally assume their full lead length, in free air, so it's safest to over-rate them by 2 to 4 times for shorter lead lengths and operation within confined enclosures). 

By the way, try to avoid using bulbs intended for flashlight service...they're often high brightness, low life expectancy...since flashlights are usually on intermittently. There are charts available showing life expectancy at rated voltages for various lamp type numbers. The lamp's manufacturer can provide this information and it's also sometimes included in the more complete electronic supply house catalogs. It's surprising how much different lamps do vary in their average life expectations. 

Dave, NZ9E   





From: [] On Behalf Of Garey Barrell
Sent: Tuesday, 16 May 2006 6:30 a.m.
Subject: Re: [TS930S] TS-940S Sub-Display lamp burnt.

Two "grain of wheat" bulbs, one at either end, with green silicone rubber "socks" over them.   Replace both while you're in there!  They are 10V  [Editor note 9V 60 mA]  bulbs, so the more easily found 12V versions are a little dim.  The "correct" bulbs are available from East Coast at:
The easiest way is probably to tilt the front panel down, although I  think I was able to do it without.   Remove top and bottom covers.  The front panel tilts easily, you remove the flat-head screws near the top on either side, then  _loosen_  the two round head screws near the bottom.  The front panel will then tilt down 90 degrees, but you don't need to go nearly that far.  There are two screws that go through the board with the clock battery on it that hold the whole "sandwich" together and to the front panel.  The bulbs actually mount through the LCD board and the leads solder to two pads on either side of the hole. When reassembling, watch carefully that you don't pinch any wires.
73, Garey - K4OAH


From: [] On Behalf Of ve3fh
Sent: Wednesday, 17 May 2006 5:23 a.m.
Subject: [TS930S] Re: TS-940S Sub-Display lamp burnt.

Thanks Garey, that is a very good explanation. Do you happen to know the Radio Shack part number for these lamps or perhaps an equivalent GE p/n? The Kenwood p/n is B30-0835-08, from East Coast these are $4.19 and from Burghardt $5.18 but I would like to find an alternative source.
Julio VE3FH

From: [] On Behalf Of Garey Barrell
Sent: Wednesday, 17 May 2006 7:19 a.m.
Subject: Re: [TS930S] Re: TS-940S Sub-Display lamp burnt.


Julio -
The 10V   [Editor note 9V 60 mA]  lamps are pretty tough to find outside of OEMs.  They are expensive, but on the "bright" side, they last 12-15 years!  You  _can_  use the fairly common 12V bulbs, but you end up with a dark area in the middle of the display.
You could try places like "Bulb Direct" or other on line bulb suppliers, or if you have a model railroad shop locally.  The green color is from a silicone "boot" that is removable to transfer to the new bulbs.
73, Garey - K4OAH








The following is the most sensible write up I have ever read about connector problems It is from the site below which contains other information and is well worth reading.  

 Next I detached and then re-attached each of the connectors mounted to the transceiver printed circuit boards. Systematically I went over each of the boards carefully; unplugging the connector, inspecting and then reconnecting each one. This process went routinely until I got to the main control board. On this board the fourth connector checked pulled completely out of the board ( the male portion of the connector completely separated from the board) leaving two very clean holes in the board. I make a note of the faulty connector and continued checking plug connections. The very next plug checked also pulled out of the board. My inspection of the rest of the connectors did not yield any more problems quite so obvious.

I removed the board, inspecting the faulty connection points, and re-soldered the plug bodies back into the board. …. 

Before removing the connectors I sketched a simple schematic and labeled it  and the plug connectors. This enabled the return of the connectors into the original configuration without doing a lot of schematic wire tracing. I removed all remaining old solder from the original plug bodies and solder connections, then re-inserted the male plug bodies into the pcb board. I re-soldered these parts back into the boards and while the board was accessible to the solder iron; I used a jeweler's loupe and carefully inspected the solder points all over the board. I pay special attention to the plug body pins for the numerous connectors on the board. This process pays off big results! I find at least 8 other connectors on this same board that are obvious cold solder connections ( the pins were obviously "floating" in the old solder, and moved visibly when touched). This discovery was very encouraging; an obvious root cause of some of the intermittent issues this rig has had in the past. I suspect that the loose plugs and many of the cold solder joints were actually caused by the WIGGLE and Plug/Unplug technique so heavily endorsed in earlier internet comments and reports. The first time it probably had good results; over time this technique actually increased the amount of transceiver issues.


I reheated the solder on the connector pads that are bad, discovering that the old solder would not stick to the plug body pins. I used a solder vacuum and solder wick to carefully remove the old solder from each of the old pins that I know and even suspect are bad. This process is repeated for any solder point that is suspect on the rest of the components on the board. As you can imagine; this process takes some time. When I completed the control board, it was re-installed into the rig, and the transistor heat sinks and disconnected plug bodies were re-installed.


After completing the process noted above; I repeated the process for each of the other remaining boards on the rig. There are 5 other main pcb boards on the rig, not counting the little specialized boards located on the back of the main panel. I went through each pcb with the same process; finding and correcting more bad or suspect solder connections. In summary total; I corrected 2 completely disconnected plug bodies, 12-14 visually obvious cold-solder connections and another 30 or so suspected bad connections on various plugs and components.






There are two

Behind switch Unit L (X412-1600-00)



On Digital A Board: (X54-1830-00)







Typical symptoms for the Switch Unit battery failing are:


From: [] On Behalf Of Jim Bazsika
Sent: Tuesday, 21 March 2006 11:44 a.m.
Subject: [TS930S] 940 clock display stopped working

Good day all,
I recently got hold of a Kenwood 940.  . .  . I have only been using it a couple of weeks and the other day the green display that shows the clock and split freq's (which was working fine up until then) had some '0's in the display, as well as some '/' symbols when I turned it on.  I shut it off and put it back on, and the display has been blank ever since. 

Any ideas as to what the problem may be??  Could it be the clock battery?  I don't know when, or if, the radio last had it's batteries changed, but I wouldn't think a clock battery would go so fast.  I don't know.  Any thoughts, ideas or suggestions would be very much appreciated.  Thanks!






From: Jeff King []

Sent: Wednesday, 22 March 2006 5:16 a.m.

To: 'Jim Bazsika'

Subject: RE: [TS930S] 940 clock display stopped working



Definitely the battery behind the LCD has lost voltage. Almost exactly same happened to my 940.


What I found was voltage on this battery had dropped to 1.7 V, Should be 3.0 V. found if I left the 940, 24 hours the battery recovered up to 1.8V and the sub display worked, for about 20 minutes, and then became scrambled letters again.


Anyway what to do to fix.

The TS-940 has internal batteries which are similar to a CR2430.  3V lithium at 285 mAh.

Have a look at this page which explains battery replacement in an 850.


Genuine Kenwood batteries

 W09-0359-05        TS-940S LITHIUM BATTERY

have metal tabs and leg pin wires on them and are soldered to the boards.


You don't need to use genuine batteries.


The table below shows many of the 3 volt dc coin type batteries you can use!!

Model Number

Capacity (mAh)

Dimensions (mm)

Weight (g)






CR 2016 RH








CR 2025 RH








CR 2032 RH








CR 2032 RH1








CR 2325 RH








CR 2430 RH








CR 2430 RH1








CR 2450 NRH








CR 2450 NRH1








CR 2477 NRH










You can buy a CR2430 at Dick Smith or Radcliff. If you want battery with legs which is easily soldered then go to Radcliff behind the Railway Station. It will take you a week to get. Maybe longer because they are unhelpful with finding small parts. But they definitely can obtain special batteries.


Any way I brought a CR2430 and soldered wires onto it. Wasn't easy to solder.


Then at Dick smith I brought two push on plugs, with legs that can be soldered directly into a board similar to those used in later model Kenwoods.





Cut one leg off the plug and solder it into the hole that was left when you unsoldered the old battery.


To get at the battery remove the top side screws on the front, loosen bottom screws and tip the front face forward.

Then un plug, take out screws  and remove Switch Unit L.


Unsolder the battery wires, and soldered in the new plugs.




Find a small enclose to hold the battery, so if it leaks the enclose contains the leaking fluid.

Attach this container by Velcro to a convenient point inside the radio.


This way next time I replace a battery it will be just a plug in without having to take the 940 apart so much.


Next time I will look at using AAA size 3V lithium in a battery holder. With the potential long life from newer AAA lithium battery may never have to replace them again.


Yours sincerely

Jeff King










While working on IF Boards the following parts were found to be missing:

Any information as to why Kenwood removed these parts would be appreciated.  If box below empty means existence of component not yet searched for.


First Edition Service Manual

Revised Edition Service Manual

Serial number 6,02x,xxx USA model

Serial number 6030687  USA model

Serial number 7,xxx,xxx  USA model

Serial number 9,xxx,xxx  USA model

















IF BOARD  R118  as 4.7K between Q13 and L17 to C96















Reason removed unknown. Any information would be appreciated.








Reason removed unknown. Any information would be appreciated.








Reason removed unknown. Any information would be appreciated.


Replaced with wire 105

Replaced with wire 105




Replaced with wire 105

Reason removed unknown. Any information would be appreciated.









Available at:



ASB0896.jpg  TS-940S LCD Clock Display Erratic Operation  81.38 KB 

ASB0900.JPG TS-940S PLL Unlock  54.42 KB 

ASB0907A.JPG TS-940S Antenna Tuner Relay Damage/Modification  69.35 KB 

ASB0907B.JPG TS-940S Antenna Tuner Relay Damage/Modification  29.92 KB 

ASB0908.JPG TS-940S PLL Unlock Due To Low Levels  91.39 KB 

ASB0909.JPG TS-940S AVR Unit Capacitor Change/Failure  104.22 KB 

ASB0910A.JPG TS-940S AGC Circuit Improvements  61.02 KB 

ASB0910B.JPG TS-940S AGC Circuit Improvements  60.39 KB 

ASB0912A.JPG TS-940S Transmitter Hum In SSB  71.53 KB 

                ASB0912B.JPG  TS-940S Transmitter Hum In SSB  41.30 KB 

ASB0913.JPG  TS-940S Signal To Noise Ratio Improvement With NB  60.94 KB 

ASB0917A.JPG TS-940S VCO/Carrier To Noise Ratio Improvements  89.43 KB 

                ASB0917B.JPG  TS-940S VCO/Carrier To Noise Ratio Improvements  59.09 KB 

ASB0917C.JPG  TS-940S VCO/Carrier To Noise Ratio Improvements  36.90 KB 

ASB0918A.JPG  TS-940S Squelch Switching Noise S/N 711XXXX  85.04 KB 

ASB0918.JPG  TS-940S Squelch Switching Noise S/N 711XXXX  53.83 KB 

ASB0918B.JPG TS-940S Squelch Switching Noise S/N 711XXXX  65.29 KB 

ASB0921A.JPG TS-940S SSB Talk Power Improvements S/N 601XXX - 708XXX  84.05 KB 

ASB0921B.JPG TS-940S SSB Talk Power Improvements S/N 601XXX - 708XXX  51.11 KB 

ASB0951A.JPG TS-940S Erratic Display (Remove The ROM Socket)  84.33 KB 

ASB0951B.JPG TS-940S Erratic Display (Remove The ROM Socket)  49.49 KB 

ASB0988A.JPG  TS-940S MFR-485 Driver Transistor Changes (Blue Dot)  79.27 KB 

                ASB0988B.JPG TS-940S MFR-485 Driver Transistor Changes (Blue Dot)  29.54 KB 


 ZL4AI found that some of the diagrams Kenwood put on the web cannot be read. Legible versions can be obtained by emailing Kenwood. It helps to point out there is considerable Health and Safety issue / liability fro Kenwood if an Amateur using information makes a mistake because the information Kenwood provided could not be correctly interpreted.








Copied from “W6NL Mods for the TS-930.PDF”



Clif Holland of Avvid, a respected repairer of Kenwood radios, emailed me to note that

the Japanese specification for the standard signal generator used in alignment is different from the US signal generator calibration.

The 930 service manual refers to signal levels in dBuV, so I had assumed 0dBuV was 1 uV and 40dBuV was 100uV.


But not so. Clif is right and I'm off by 6 dB. I checked it out, and although I see no mention of the issue in the TS-930 or TS-950 manuals,

I found a table in the TS-850 service manual, pg. 96, that confirms this. It has two columns:

Japanese "SG"                        American "SG"

-6dB                                      0.25 uV

+0dB                                       0.5 uV

+6dB                                       1 uV

+12dB                                      2 uV

+24dB                                      8 uV

+30dB                                     15.8 uV

+40dB                                   50 uV

+50dB                                  158 uV

+60dB                                500 uV

+80dB                          5 mV



Apparently the JA generator defines output in terms of open circuit voltage rather than voltage into a matched load. This 6 dB difference affects the alignment of the RF PIN attenuator start point as well as the S-meter settings for S1 and S9. Since the manual specs are 4 dB anyway the difference will be mighty small except for a more active S-meter.


 S meters revised from here on at version 25



ZL4AI adds:

from page 78 / 79 of the TS-930 service manual, confirms the above:

Japanese SG 0dB = American 0.5 uV


from page 51 of TS-940 Operating Manual

If a standard signal generator ( SSG) is available, adjust VR-4 so the S meter indicates”S-9”, at 14.175MHz for a 40 dB (50uV) signal


from page 69 of the TS-930 service manual

SSG output: at 14.175MHz 100dB /u:  =  S meter reading S9+60dB +- 6dB


100 dB/u S-meter maximum calibration information seems to be unclearly laid out in the TS 940 service manual, but is inferred in the accompanying notes in the TS 940 service manual. It looks like Kenwood’s made a typo and missed it out.


from page 101 of the TS-850 service manual, (are different values to those used on the TS-930 and TS-940

Standard Signal Generator 14.100 MHz, AGC OFF

S0: Output set VR12 to 0.1 V +- 0.01V


S1: Output + 6dB                 Tolerance within +- 3 dB

S9: Output + 32dB               Tolerance within + 4 dB, -8 dB



TS-950SDX values not included because S9 meter readings not stated.




The TS-940 Service Manual below on pages 72-73 is not very easy to understand:





ZL4AI prepared extended service instructions below:






Specification / Remarks

American Signal Generator

RMS volts


referenced to 1 milli Watt



Test equipment










S meter

BAND: 14.175MHz

SSG output : 14.175 MHz 0dB









Adjust meter needle for mechanical f


0.5 V



-113 dBm











Set the VR1 to CCW





S meter

SSG output:    8dB







ADJ to S1

S1:              8dB    + 6dB

                             - 4dB

1.26 V


> IARU usual  0.19 V for S1

 -105 dBm


16 dBm > IARU usual    -121 dBm  for S1,

= 2.7 S units


SSG output:  40dB






ADJ to S9

S9:             40dB   + 6dB

                             - 6dB

50 V

 -73 dBm


SSG output: 100dB






Verify full scale

S9+60dB:  100dB + 10dB

                           - 10dB

50,000 V

50 mV

-13 dBm








Repeat ADJ S1 and S9





Red are items Kenwood missed out






S meter Information



IARU Region 1 Technical Recommendation R.1 BRIGHTON 1981, TORREMOLINOS 1990

Page 1 of 1




1. One S-unit corresponds to a signal level difference of 6 dB,


2. On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals,


3. On the bands above 144 MHz this available power shall be -93 dBm,


4. The metering system shall be based on quasi-peak detection with an attack time of 10 msec 2 msec and a decay time constant of at least 500 msec.





Rob Sherwood NC0B,

who seems to lead thinking about receiver design performance measurement quotes:

Assume S9 = 50 V which is –73 dBm


The -73 dBm power level calculates out that 50 V is an RMS value. {Not peak to peak}

This enables preparing:


S Meter reading


(dBm) *

Voltage at receiver input

micro volts, V, and millivolts mV)


S9 + 60 dB


50.06 mV


S9 + 50 dB


15.83 mV


S9 + 40 dB


5.01 mV


S9 + 30 dB


1.58 mV


S9 + 20 dB

- 53

500 V


S9 + 6 dB

- 67

100 V



- 73

50 V



- 79

25 V



- 85

12.5 V



- 91

6.2 V



- 97

3.1 V




1.6 V




0.77 V




0.39 V




0.19 V

Kenwood 940  uses 1.26 uV, = -105 dBm

               (* dBm is power expressed as decibels relative to one milli watt)


To Calculate between V and –dBm see ARRL Handbook 2004, page 30.14 which explains all the calculations, and formulas.






dBm values quite interesting to compare with other expert observations, that is S Meters are not linear:


To:  <>

Subject:  [AMPS] s meter calibration

From: (Larry Molitor)

Date:  Tue, 13 Jun 2000 22:57:40 +0100


At 07:45 AM 6/13/00 +0100, Ian White, G3SEK wrote:

>According to the lab reviews in the magazines, most modern receivers seem to be calibrated so that the difference between S9 and S9+20 is pretty close to 20dB. Below S9, the scale looks linear but the dB per S- point is not1 It typically takes many more dB to get from S2 to S3 than it does to get from S8 to S0 - often less than 3dB per S-point at the top end.

>It doesn't have to be that way - there are engineering solutions that could easily deliver the full IARU specification - but when everybody on HF is "five nine" anyway, who cares any more?

>73 from Ian G3SEK



Ian and all,

As has been said before, the manufacturers correctly assume that the  majority of buyers are technical idiots. Have a S-meter that has 1 dB per  S-unit and about 5 uV for S 9 is a good marketing thing. Besides it's a lot  cheaper to build. I would hope that anyone who actually cares about such things would take the time to "calibrate" the meter on their store-bought radio. Since I do  this with all my radios, I would not care to pay extra for a manufacture to make a feeble attempt at a real meter.


Using a HP8648C generator (at 14.1 MHz) this last time, I produced the  following chart for my FT1000D:


S1 = -103.5 dBm

S2 = -101.5 dBm

S3 = -98 dBm

S4 = -94 dBm

S5 = -90 dBm

S6 = -85 dBm

S7 = -80 dBm

S8 = -75 dBm

S9 = -70 dBm

+10 = -60 dBm

+20 = -51 dBm

+30 = -42 dBm

+40 = -33 dBm

+50 = -24 dBm


As you can see, it's kinda poor at the bottom end, but quickly stabilizes  at about 5 dB per S-unit. With S-9 being within 3 dB of 50 microvolts and 5 dB per S-unit, this particular FT1000D has the best S-meter out of the 10 or so radios I've checked.

               With a chart like this handy, it gives you a real good idea just how good the other guys antenna is or how much gain his amp really has. While the guy on the other end is usually an idiot and won't believe what you tell him, at least you will know for sure.

               Since it's so easy to do this, I'm surprised there aren't more folks with handy little charts for their radios. I know, not everyone has a room full of good test equipment. But I bet most people on this list know someone who does or has access to it one way or another. Give it a whirl, you might be amazed!


Larry - W7IUV









Kenwood failed to observe the same standard 



From Item 10, page 95 of TS-870 Service Manual, year 1995

Standard Signal Generator 14.101 MHz,


S0: Output -110 dBm

S1: Output -107 dBm

S9: Output -81 dBm

S9 + 60dB Full Scale (lights up all) Output -23 dBm



TS-2000 or TS-480, changed to:

From Item 21 TS-2000  Service Manual, year 2000

From Item 10, page 64 of TS-480 SAT / HX Service Manual, year 2003

Standard Signal Generator 14.201 MHz,


S1 Output -107 dBm (1v)  

S9 Output -81 dBm (19.9v)  

S9 + 60dB Full Scale (lights up all) Output -21 dBm (19.9mv)  










(800) 637-0388

East Coast Transistor has an online data base with part numbers: Very helpful in identifying the correct part. They also supply some parts not listed on the database.


From: []
Sent: Wednesday, 20 September 2006 6:10 p.m.
Cc: Jeff King

 Thomas & Jeff   : I found a Website where they sell the digital board for my TS 940 S also their prices for IC's much lower than anywhere else. For instance East Coast Parts  Kenwood Approved dealer) sells an IC for $7.50 at part store its $2.50  Site is

 Regards Bill Cridland WA1HMW


Editors Note: For a 930 Digital A Board CPU parts charges $65 compared with East Coast charging $95.

Looks like a 30% saving








Kenwood Corporation

Kenwood Electronics Australia Pty Ltd

Kenwood Electronics Europe UK



K0BX Kenwood Interface HomePage

850 Repair Page

K0BX Kenwood Interface HomePage

Piexx Company - Home

International Radio Service Division

QSL.Net Index

Yahoo! Groups : TS-940 

Yahoo! Groups : Kenwood TS-950SDX 


The Defpom Kenwood Radio Modifications Page


K0CKD's Topband/Kenwood Resources & More!

The Kenwood Archives

Martin Sole        This is actually the First TS-940 page, and holds quality information.

K4NR repairs

Geihl Chip







More information on the Pin Diode Improvements would be appreciated







A lot of reviews found at
















TopBand: Comparison of TS940 to newer receivers


Tue, 15 Apr 1997 12:35:24 +0000 (GMT)  

April 14, 1997  

A number of weeks ago I asked the TOPBAND reflector about their  experiences with newer receivers, and promised to summarize your comments

and my tests for the group.  

I'm slow in getting this out because I lost some mail messages (including my  own) but here's what I pieced together:  

****Comparison of Kenwood TS-940 to other Receivers****

(This test is aimed at CW reception)  

MY ORIGINAL QUESTION (my own comparisons are at the end of the message):  

As a died in the wool TS940 user, I've been believing that the 940's receiver was as good as I could find for 160 and 80 meter DX CW, short of some of

the older rigs (like the Drake and Collins stuff). Even though copy is rough here in the "black hole" of DX, I have been able to work a number of

countries on these bands with just 100 watts. Line noise at my place is MAJOR!  

Then I visited N9QCT to see his new TS-570 on a trap vertical.   What I hear on the 570 amazes me. It's early evening, when all I hear at

home on 160 M is static. And his 570 is dragging in European signals above  the background noise. When he kicks in noise reduction (NOT the noise

blanker) the CW sounds like it's a code practice tape! On 160! Not only that,  but at the 50 hz filter bandwidth (actually about 80-90hz) there was

practically no ringing. I plan to borrow his rig and try it at my place  with better RX antennas and the heavy line noise, just to get an apples/apples comparison.  

So the question to recent buyers of new rigs is: Compared to your experience with older "top-end" receivers (like the 940 WAS

ten years ago) how do the new receivers stack up? I know that audio DSP  will overload without a mechanical filter as well, and I saw it on Eric's 570

(he has a 500 Hz filter on order). But what about fully loaded TS570, TS870,  FT1000MP, Omni VI, etc?

What differences do YOU notice?



(R4C about same as TS940, per AA1K)  

I'm a 940 user too, in a high noise urban area (1000 feet from Amtrak line  and major power transmission line, etc.) but have an array of Beverages

that help overcome the noise. I've not had anything newer here to compare with,  do have an R4C with Sherwood mods and find it about neck-and-neck with the  940.

Also use a DSp 59+.

73/Jon AA1K


(Fixing the 940, from KM1H)  

T'aint nothing wrong with the TS-940 that a little work won't cure Mel. Depending upon the serial number ( 8 Million a rough cut-off) there are

many to some mods that really help. Private E-Mail me for specifics. (KJ9C NOTE: MY 940 IS ONE OF THE NEWER ONES, SO THAT AIN'T THE PROBLEM)  

Also by changing about 45 diodes over to PIN's there is a dramatic performance improvement in RX performance. I also use cascaded IRCI

filters for both CW and SSB...the Kenwoods have poor skirt rejection.  

I have 4 940's here that are used fm HF thru microwaves as platforms for transverters. I quickly sold a FT1000D as not worth the money that 2 well

modified 940's could perform at.  

I had a TS870 here on has a great RX but very prone to overload on  40 thru 160.  

GL and 73    Carl  KM1H   261 DXCC on 160;    309 on 80


(Comments from George Guerin..K8GG)  

     1. My experience with the TS-940 is it does not hear as well as the   TS-930 or TS-950SDX.  Also there is generally a spike on the leading

 edge of the first CW character sent which risks grid damage to tubes   like the 8877, 8874, 3CX800A7, etc.  

     2. Your description of the TS-570 sounds very good.  Maybe they will  make a TS-970 soon??  

     3. I hear there are problems with the TS-870, because there are no  filters at all, except digital in the last IF.  This creates birdies

in the pass band, since it is at something like 14 or 17 Khz, and a signal 28 or 34 Khz away can leak through.  I hear one W6 added

filters and cleaned the birdies, but Kenwood will not do this on  production units, so we will have to wait for a TS-871 or 880?  

     4. I have used the FT1000MP and it does a pretty good job, but I  haven't put it side by side with other radios.  Setting the two DSP

controls on the concentric rotary switches is a bit tricky.  The dual receive and or split is very good and easy.  A friend in Chicago says

it hears better on CW than the FT1000D and the TS950SDX.  On phone I  like the TS950SDX best, but that is not true 160 operation.  

     5. I would like to try the IC-775.  More money, but the automatic  carrier null is very fine.  On CW, I would like to try one on 160 for a while myself, and see about the noise removal system.  

     6. I understand TenTec has a Omni 6+ just out with dsp.  I have no way of trying it and the TenTec "chemistry" and my body chemistry do not

get along, so I will never buy one.  I do have friends on 160 with  Omni 5 and Omni 6 radios doing well.  They do have good beverages.

One has a directional vertical array!!  I do have a TenTec tuner I like a lot.  There is no chemistry problem without electronics inside

the box!  HI !  

     George Guerin


[NE3H compares the 940 to the Omni VI (not the VI+)]  

On the OMNI .. no question, best receiver that I've ever heard.  Yes,  I think the FULL DSP receivers may be more sensitive ... or have lower

noise floor .. but none of the HAM gear that I am aware of ..  

I cannot hear the diff between my old 940 and the OMNI .. if normal ambient noise, most people cannot hear the diff.  The outstanding

characteristic.. and the second reason I got TWO OMNIs .. is that you can have an S9 + 20 signal next door to one in the mud .. and it does

not make a difference.  I have a neighbor .. a mile away .. who runs a kW on RTTY .. ( as do I ) and we can op within a Khz or two without

disturbing each other.  

Fact is, if you have lots of line noise .. I don't think you'll notice the diff in rcvr sensitivity.  The noise blanker on the OMNI is about as

effective as any .. but I don't think it is better than the 940 re noise blanking.  But Yes .. the front end does not 'Block' in the presence of a loud signal next door ...  

The second reason that I went for the OMNI is that it's signal on CW / QSK ( at high speed ) is distinctly better that anything else .. save the Icom 781 that I've heard anywhere else.  

The fact that you can cascade filters on the NEW OMNI PLUS really makes me twitch .. I've already signed up to do the full upgrade to my radios. I have a 500hz RTTY filter in the 9mhz path .. after the mod .. I'll be able to have a choice of the RTTY filter or the CW filter .. I think that is

a real advantage ..  

Of course, stacking of filters is pretty nice on the FT1000 stuff too ..  

The OMNI operation is pretty intuitive too .. it has less bells and whistles .. but I can't think of any I miss ( from the old 940s ).  

Remember that 98% of my operation is CW and RTTY.  

de joe


(comments from K3SME)

Were you able to borrow the rig and try it at your QTH?  I have found that 160M performance is very QTH specific.  I have borrowed "goodies"

like DSPs which knocked noise down ALOT at my buddy's QTH but didn't do much for my noise here as an example.  One of the locals here in

Maryland picked up a 570 about 2 months ago and after a week said it was pretty good but he HAD to get the optional filter to make it decent on

low band CW for receive.  Have you had other comments?  The few guys I know with OMNI V and VI praise them highly for low phase noise and

tremendous RX capabilities.  I am using a TS830S.  It replaced a Drake 4 line. Tough to keep up with technology and I refuse to pay for a 100

memory tranceiver when I don't need all those bells and whistles.

73, Sid.


(K8GG asks about the 570, comments on TS950)

Have you read the review by Doug DeMaw, W1FB in the March 1997 issue  of CQ Magazine?   It reads well but raises the questions I have

written here below:  

1. I wonder if the only way to get a beverage hooked up is to change antenna selections on the front panel?  

2. I also wonder if there are plug in slots for more than one extra filter?  I don't need a 1.8 Khz SSB filter with slope tuning, but I would like to have both the 500 and 270 Hz filters in the 8.8 MHz IF.  

That is one complaint about the TS950SDX:  There is room for both the 500 and  250 Hz IF filters in the 455 Khz IF, but only one CW filter in the 8.8 IF, and it is more important to have selectivity in the first possible stage (2nd IF) rather than in the next stage (3rd IF).  

Obviously, it does not have the DSP available in the TS570!  

I may send Doug an SASE and note and see what happens.  He now lives  maybe 175 miles NNW of me.  

     73         GL              George          K8GG


(Another comment from K8GG George Guerin)

As I saw the TS-870 show at the W9DXCC a couple of years ago, there are NO IF filters.  That model uses digital filtering at about 17 Khz

to shape the passband.  Problem is the images 34 khz away!  

There is no plan to put in filters, although a couple of California  hams have done it.  (WONDER WHO?) With out a 2.7 Khz filter at the 8.8 or 455

IF, it has troubles from what I know.  

Kenwood is NOT planning to make filters optional.  I do understand using the SSB filter and digitally making the CW filter in the 4th IF

works fine.  

On the TS-570:  Is there an accessory socket like the TS-940 and TS-930 that has the ability to pull out and put back in the RX antenna


That is my fear!    The Icom radios like the '740, '751A, '765 and  '775 all have a coax jumper for the RX antenna line.  The '728 and '726 do not!!  I complained to the Icom rep's at Dayton.  

The TS-950SDX has a jumper like most of the Icom radios.  

There is a guy in Ft. Wayne who makes FEP's - front end protectors. If you  can figure a way to bring out the RX antenna line, it is a neat

way to make sure the RX input is grounded on transmit.  It is written  up,  but not in enough detail, in one of the recent CQ Mag's as well. That might help, but toggling the front end on each "over" is a true


Have fun,  73   George


MY OWN TESTS, Side by side with TS-940... KJ9C  

>From what I saw of my friend's 570, and from his comments, the CQ article is on the money  

To switch antennas one must MANUALLY hit the ANT switch... so that's one hit for transmit, one to receive when using a beverage... I have not yet

looked for a transverter input on his rig, as that is how my TS-940's  external RX antennas are wired,... when I get the rig at my place I will

check for features... but I know there is NO dedicated RX antenna  input... this would keep me from buying a 570, but I guess I could build

an external TR switch like we built back in 1968 for club's S-Line.  

There is room for only ONE filter... so decide whether it's SSB or CW,  500 or 270... that's a big drawback but would not keep me from buying a

570, as I would likely go for the single 270 for IF protection... but one in each IF would be nice... I guess the TS870 has room for NO IF filters  

Written later:

I borrowed the 570 for a few hours and installed it with antenna switching next to the TS940 at my NOISY QTH (line noise on some antennas as high as 20

dB over S9). In every case the 570's noise REDUCTION unit did a better job  of reducing noise and bringing up weak signals (most tests on 160 and 80

meters where my noise is worst). The noise blanker also worked, but the digital  reduction was better. On the contrary, the noise blanker on the 940 seems to

be a little better than the 570's.  However, as you know, strong signals tend to swamp receivers with noise blankers ON. The 570 noise REDUCTION beat the DSP59+ NR feature.  

The 570 was tested without an IF filter installed, and it did exhibit some overload from adjacent signals... since then, Eric has installed a 500 Hz

IF filter and reports that adjacent signal swamping is negligible, and he can  crank the DSP down to 100 Hz without ringing.  

The DSP is the selling point of this receiver... better signal to noise than the 940 (with STRONG noise) and therefore can dig out the weaker ones.

However, in the absence of strong line noise (say S3 or lower) the TS940 with outboard DSP seems to work pretty well. See below.  

The CW autotune works with relatively weak signals, but not down in the  mud. This makes tuning with tight bandpass a lot easier.  

Very little SSB testing, but the heterodyne filter works as good (or  better) than the one on the 59+ DSP. Did not have multiple heterodynes to

see how it works, but would guess OK.  

Forgot to check for transverter input!!! Dope! Suppose that auxiliary  receive antenna is possible somehow.  


I borrowed K9IG's 1000MP for similar testing. I felt like I should sign away rights to my firstborn grandchild if I damaged it, so better believe I

was REAL careful with it and read the manual first!! But Greg seemed unconcerned that I was driving away with HIS 2500 dollar radio in my truck.  

I set up similar to the TS570 test, and as luck would have it the power company chose to temporarily fix the line noise (after five months!!!) that

day. With all the mechanical and DSP features kicked in (including a DSP59+ on the 940), the TS940 and the FT1000MP performed about the same on 160 through the other bands (CW only tests). Some of the controls WERE tricky, and the preset filters on the 1000MP took some getting used to. There must be about two million bells and whistles on the 1000MP, and my fat fingers found a few by accident. It is an impressive rig... but without line noise, not enough to make me dump the old 940. Without the noise reduction, the 940 is OK.  

One thing I noted... small point... S meter readings were comparable for both  rigs at low signals and noise levels... but S meter readings were higher

on the 940 for stronger signals... of course, that does not mean much, as an S meter ain't that accurate... just needed more attenuation with 940.  

I packed up the 1000MP and got it ready to take back to Greg (about 8 miles  from me)... then Indianapolis Power and Light came through just in time!!!

Line noise returned, but only at S9 levels. I quickly patched the 1000MP back into the setup and compared reception. In this case (with strong line

noise), the 1000MP was better at pulling weaker signals up out of the crud. Even with noise blanker on, the 940 lost some of its ears. Noise blankers on

both rigs eliminated the noise HEARD, but the 1000MP was better at finding signals and bringing them up than the 940 with DSP59+ was.  

4/15: Bill Tippett reports that his 1000MP is extremely clean (no intermod products observed) compared to the TS930 he retired.  


I wanted to test an Omni VI+, but none to be borrowed locally, so I asked  NE3H for his opinion (see above). In the meantime, power company has repaired a number of defective lightning arresters, a bad transformer, and God knows what else to the point where my line noise is now S3 or less most of the the 940 gets a reprieve. I fact, even though it's almost too late in the season, am working DX on 160 most evenings now when I could not hear it in winter!!! With a little luck I might hit 50 countries for the 96-97 season.  

I wish I could find the mail messages I sent to George because there was more specific info in them... but this report is the bottom line. From my own observation, the 1000MP and the TS570 outperform the TS940 receiver with high line noise levels. Mechanical filters are needed on both rigs. But with little line noise the 940 is still pretty dang good.  

Thanks to K9IG (formerly KO9Y) and N9QCT for the loan of their rigs.

Mel KJ9C 


FAQ on WWW:     






-----Original Message-----

From: [] On Behalf Of Mike McCarthy, W1NR

Sent: Wednesday, 13 July 2005 1:13 a.m.

To: Philip Neidlinger;

Subject: Re: [Kenwood] "New" TS-940S

----- Original Message -----

From: "Philip Neidlinger" <>

To: <>

Sent: Tuesday, July 12, 2005 8:45 AM

Subject: [Kenwood] "New" TS-940S


>Yes I know the 850 is probably a better rig, but I like to have an analogue meter on my radios.


No it's not!  The quad conversion of the 940 blows the doors off the 850.

I've used them side by side.


Mike, W1NR



 UPDATE: (8/17/03)  After two months of using the Orion (and one repair trip back to TenTec), I have sent the Orion back to the good people at TenTec for a refund.  It is a long story why I sent it back, but the short of it is that the Orion just did not meet my expectations.  It has a lot of good features, but it just isn't what I was expecting.  I found the SSB receive to be muddy and difficult to copy even if the signal was strong.  Maybe it's just my ears, but I found my Kenwood 940 to be a better radio.  The Orion is a very noisy radio, at least mine was, and the dsp really did not do much to make weak signals more understandable.  After 6 weeks of only using the Orion, I finally hooked up the Kenwood on an A/B switch.  I spent several hours looking for only weak, at the noise level, signals.  Hands down the Kenwood ran rings around the Orion for weak signals.  Signal levels were about the same on both radios, but how the audio sounded is the key.  On the Orion, weak signals were muddy and difficult to understand.  The Kenwood brought out those same signals and made them easily copyable.  If you cannot understand what someone is saying, you cannot communicate.

That being said, I will also commend Jack Burchfield and the other people at TenTec who listened to me and really tried to help me.  TenTec is an excellent company and their people are dedicated to their customers.

So what did I do?  I went out and bought a Yaesu FT-1000D.  What they say is true.  It is the king of radios.  There is a lot to be said about good old fashioned stacked crystal filtering.  Nice rounded smooth audio is what my ears want to hear.

So, for now, that's the story from the shack.














-----Original Message-----

From: John []

Sent: Sunday, 10 April 2005 3:06 a.m.


Subject: Re: Advice on what to do upgrade TS-940 PowerSupply


First thing


Replace all the Zener diodes on the AVR board with 1 watt Units. Same voltage values. you will have to open the hole up slightly to allow for larger leads on new parts








D-1, 2 ,10-13 are all ok ... just leave them. They are 2.5amp at 100Vpiv



Q-1  and Q-2 , Q-6 are fine. Just replace them with same.


replace C-3 ,C-4,C-6 with 2200UF 50volts , replace C-13 too.


Put a 47 ohm 1/2 watt resistor in series with the collector of Q-6 to limit inrush current on turn on.


Replace the pass transistor Q101, Q102 with 2N5886 ......if these short it puts 42 volts on final unit

and burns out the expensive driver transistor in about 30 seconds


Resolder the complete board & deflux it too.





Observations by ZL4AI


Original Diode Specifications:

ZL4AI thinks the file below gives MTZ diode operating values.




Possible Replacement Diode Specifications:







1n4728A to 1n4753A Hitachi.pdf







Original 1

Original 1

Measured in service at:

Replacement 1

Replacement 2

Measurements taken on replacement

D1, D2, D10 to D 13





1N5404  [400V 3A]


[1000V 3A]



500 mW












500 mW




















500 mW


19.72v to 20.72v


22.05v to


ZL4AI measured for diode ‘marked 22D’,  22.8v


DF5KF measured 22.7v




22v +- 5%

21v – 23v




20v +- 5%

19v – 21v





ZL4AI put in


and measured



pin 5-21T on AVR  20.7v








D9 is difficult to find a replacement match for

Kenwood Original is MtZ 9.1 JA which has voltages between 8.29 -> 8.73  median  = 8.53V

Kenwood alternative part is MtZ 8.2 JC which has voltages between 8.03 -> 8.45  median  = 8.24V


Possible replacements

1N4738  8.2 V  +- 0.5V

1N4739   9.1V +- 0.5V


Installed and measured I found

1N4738 output 7.27V at AVR terminal 9 pin 8  ie. 0.63 Volts too low

1N4739 output 8.31V at AVR terminal 6 pin 1  ie. 0.31 Volts too high


D9 only supplies the liquid crystal display and the remote control IC in Digital A, it is very unlikely to have 0.5 watt drawn from it. Very few 940s have the remote control chip installed. My conclusion was it was best to leave in the original diode putting out 8.0 volts.






 From Eham

 RE: Kenwood ts 940s avr board  Reply 

by N0XWR on February 28, 2006 

you won't find an AVR board for sale new. you should endeavor to fix the one you have. first, check regulator Q103. it is in the rear left corner of the rig as the rig faces you. it is on the heatsink for the power supply. there are three regulators side by side. it is the one on the far left. no matter whether you replace it or it is good, it is imperative that you cut the connector off of the three wire harness that plugs on to regulator Q103 and solder directly to it. this harness comes from plug-in #2 on the AVR. over time the connector overheats and fails and cannot carry the 20-30 volts to and from that regulator. i have seen the problem many, many times. when the connection to that regulator fails, it takes out Q6 on the AVR board, so check it next. clif at AAvid, now retired helped me get through the problem. also check D3, D9 and D14 which are zener diodes on the AVR board. they can be checked right on the board with a multimeter. the board can be removed easily. as you unplug the wiring harness use a sharpie and number each connector so that you can reinstall it easily. make a diagram, too. use small long nose forceps to unplug the connectors to the AVR board. Incidentally, Q103 is part #NTE377 available at mouser. Q6 is part #NTE382 also available at mouser. i have the part numbers for the zeners if you need them. 73s Jerry N0XWR 








This mod to your TS-940 will change the ALC delay time from approximately 1 sec to 0.022 second.  This means that the ALC

will no longer impose its own time characteristics on your audio response; the ALC will now follow your own sylabbic

rate amd emphasis.  Usually the average power output will increase which will drive a linear amp harder.......(at least

those meters will swing higher!).


The TS-940 has a 10uF cap (C31) and 100k resistor (R104) which make up the time constant for the ALC.  This tends to

reduce the output power for the duration of the ALC time constant (or till the circuit charges up again).  Then it starts all over again on the next word.

This procedure allows modification to the Control PCB (X53- 1420- 11) in the TS-940 WITHOUT having to remove the PCB. Remove the bottom cover and locate the Control PCB.  Locate R137 and R104.  These are located in the upper right hand corner as the rig faces you upside-down (near VR3).  A

Service Manual would be very helpful for locating parts!!! using a knife edge or similar, carefully scrape off the insulation from the top of the two resistors.  Tack solder an 1/8 watt 2.2k ohm resistor from the top of one to the top of the other.  Put the cover on and it's finished.














On the air conversations concerning a kenwood newsletter mod to change ALC delay time  called for putting  a 2.2k ohm across the top of r137 and r104 on the control p.c.b , along with a .47 mfd cap between pin 1 and pin 2 of connector 8 on  the control board. The mod is excellent except .47 mfd is far too much.   instead use  a .005 to .01 mfd to keep from over driving.  electrolytic not necessary, but if used, make sure nagative goes to shield wire pin..



TS940S owners may wish to use FSK mode for HF packet. FSK cannot be used for Packet transmit because the shift is 170Hz, and Packet requires 200Hz shift. This necessitates using LSB with AFSK. I'm not aware of any way to adjust the shift, and 170Hz is required for FSK on AMTOR and RTTY. It would still be nice to use FSK for receive, the primary advantage being the availability of CW filters which are inaccessible in LSB mode. By using the SPLIT capability you can use LSB for transmit and FSK for receive. Tune in signals with VFO-A on LSB. Then press A=B, switch to VFO-B, enable FSK, enable RIT and tune the offset to exactly -2.3KHz. Then enable SPLIT. When listening to signals,

depression of T-F-SET will allow you to listen alternately with each VFO; the signal tones should be identical. If they are not, adjust the RIT on VFO-B (FSK mode) until they are. Optional CW filters are switched in by selecting the NAR ("narrow") filters with the NAR/WIDE switch (LED indicates NAR).


I have found that this arrangement works quite well, and enhances the readability of received packets, especially under heavy QRM and fading. It is easier to adjust the CW filters (NAR/WIDE and VBT in WIDE mode) than the SSB Slope Tune controls.

I would like to hear from other TS940S users who have tried this technique or others that enhance HF Packet operation. Send replies to WA1FMM @ W8AKF. 

73...Dan / WA1FMM / Thousand Oaks, CA.





I would be most interested in getting Information on how to use an additional receiver at the same time as the TS-940S is in operation (receiving, of course).  (ED Note:  We covered adding another receiver to 930, Issue 59, Page 54.)  The User's Manual covers use of an additional receiver in lieu of the receiver of the 940 receiver section.  I am the owner of a 75A4 which I've modified and updated over the 30 years I've had the receiver, and I find no other receiver comparable to it in many most significant ways.  So I would very much like to know how to connect the 75A4 into the TS-940S for use simultaneously with the receive section of the latter.  If this subject has already been covered in a previous newsletter, please tell me how to get a copy.  (ED Note:  Nothing published on this in back issues.)  I'm confused as to whether I need to cut diode

130 and 135 on digital Unit B in order for the Xcvr to operate over the same frequency range as the receiver. Somewhere I noted that only diode 130 need be cut.  (ED Note: Kenwood Newsletter No. 54 clearly states:  D135 is for MARS frequency only.  D130 is for Gen.Cover- age Transmit.)




a chip available from Giehl electronics in  Cincinnati that will slow the tuning rate to 2 khz per revolution  on the main dial of a kenwood ts-940





















-----Original Message-----
From: DGB []
Sent: Tuesday, 5 April 2005 6:46 p.m.
Subject: Re: [Kenwood] TS-940 Full description of AGC timing improvement which significantly improves receiver performance



Excellent job on your efforts/compilations Jeff.


73 Dwight W9YQ





-----Original Message-----
From: Curtis Benjamin []
Sent: Wednesday, 11 May 2005 1:39 a.m.
Subject: Thanks


Jeff, thanks for setting up the TS-940 page. I hope it "takes off" and becomes "the" spot for '940 info.






-----Original Message-----
From: Ed []
Sent: Monday, 23 May 2005 7:18 a.m.
Subject: TS-940S Reciprocal Mix.Noise Mod - Correction




Congrats on your fine TS-940 Web Page. Keep up the good work!


I wish to point out a text error in the letter  from Rich, WZ4Z, regarding

resistors R120 and R129 in the PLL Unit  which should be corrected to

3.3KOhms each, NOT 3.3 Ohms as stated. This refers to a Kenwood fix given in

their Bulletin 917 dated 3/2/87.


Also, your  AGC Timing Correction was applied on my rig (SN 806XXXX) and

worked great! Sure enough, resistors R149  (68K on my equip) and R150 2.2Meg

had been incorrectly installed by the Mfr.  The board markings for those

resistors were wrong.


I am also following with great interest  the developments regarding  FETs

reversals noted by PY1NR.



Ed Alves KD6EU







-----Original Message-----
From: []
Sent: Thursday, 2 June 2005 3:37 p.m.
Subject: ts-940 stuff


Hi Jeff,


Im getting my first 940 hopefully sometime next week. Ive been reading your website and it has some very helpful comments and recommendations. How hard was it to make the resistor mods you describe on the IF board? Also, I found an SO-1 for mine, how difficult are they to put it? Have you done any pin diode modifications? Thanks for the great website, 73












-----Original Message-----
From: Traian Belinas []
Sent: Monday, 13 June 2005 5:05 p.m.
Cc:; 'thomas hohlfeld'
Subject: Re: TS-940S - Some few considerations


Hi all,

Jeff, thank you for keeping me informed about the TS940 work and about your website, and please continue doing it...
Please also pass any usefull info to me also, I am interrested about.

Using switches for comparison of the normal/reverse FET state may be not feasible, even in the case of using shielded cables.
The added hardware (switches and cables) will unbalance the mixer in the case of Q4 or may cause other Rx problems in the case of Q10, so the comparison may not be made this way or can be irrelevant.
A better aproach shall be using hole contact pins for the FETs and reversing them one or another position for comparison.
Don't let the contact pins there, don't forget removing them as the Q10 runs at high drain current, and so it runs normally very hot and its cooling is made mostly by the terminals conduction and by the PCB traces path....

Tnx & GL,
Traian Belinas, YO9FZS



-----Original Message-----
From: Jeff King []
Sent: Sunday, 12 June 2005 5:34 p.m.
To: ''
Cc: Traian Belinas; 'thomas hohlfeld'
Subject: RE: TS-940S - Some few considerations


Hello Eduardo,


Thanks for the email. As you will see last year on your comments page I was very inspired by your discovery.

I was like many 940 owners very excited.

After doing the research, on my web page I was disappointed to find that turning q10 allegedly made the front end unstable. 

So for that reason I have not done that.

Have you any more information on turning q10 around?


I have turned q4 around on my radio.


In the end I am drawn between two view points

-          2SK125 FETs function the same in both directions as Thomas has measured, so turning then\m around makes no difference [the scientific view to which I subscribe]

-          2SK125s make a lot of difference turned around, which makes the radio overload with the resulting gain.


Here is suggestion that you could carry out to prove your point, and publish further.


If you connect the D + S leads of the 2SK125 to a shielded lead and a switch so that the switch in one position is the normal factory setting, and in the other position it is the PY1NR setting then you could swap the positions while listening to the radio and verify just how effective the reversal is. You could report it by S point variation on switching.

If you could prove the point more, all hams would be very appreciative, of your good work.


This could be done for both Q10 and Q4 … 2 different switches. These could be mounted on the right side of the top hatch, and act as more adjustment controls for the 940.


I thought about doing this for R149 and R 150, but decided it was not necessary. Now with R149 and (150 swapped, I have to turn on 10dB or 20dB attenuation to diminish a strong signal.


Re solder joints and connectors. I already have a section about this on the web page. It needs more work and more information on soldering especially. You of course are correct about that but it is a separate matter to reversing the FETs.

There is another possibility. I actually fund on my PLL board a missing trace!!!! Wow. This meant the oscillator never worked on my radio. I’m sure some other 9404s also have this problem.


Yours sincerely

Jeff King zl4ai




-----Original Message-----
From: Eduardo Guisard []
Sent: Sunday, 12 June 2005 9:28 a.m.
Subject: TS-940S - Some few considerations


Hello Jeff,

PY1NR asked me to also say that he modified 2 (two) TS-940S, from 2 different originations. The same improvements of gain and AGC were found. He cannot precisely measure the gain improvement due to poor instrumentation.


He also wants to emphasize that is very important to fix all contact fails (very common in many TS-940S). The contact fails could "mask" the improvements that the modification may occur.


There's  another Brazilian ham that did the mod and found no difference the first time. But later on he found a defect on the VR2 trimpot. After this correction he got 6 dB more at 1,8 Mhz and 12 dB at 28 Mhz. It's also very important to fix all eventual defects before the make the mods described by PY1NR.


Thanks and regards




-----Original Message-----
From: Eduardo Guisard []
Sent: Saturday, 11 June 2005 10:51 a.m.
Subject: TS-940S


Hello Jeff,


I am PY1BR and together with PY1NR, we include all details about this MOD in my website The error was found by PY1NR.

We know that in some cases the differences in the Rx performance or gain may not be important if you correct the FET position on the PCB.


Please, let everybody know through your homepage about all comments we received from many Hams in

There are many people around the world that agree with improvements after the FET's correction.

Thanks and regards





 -----Original Message-----
From: Martin Sole []
Sent: Tuesday, 4 July 2006 12:54 p.m.
Subject: TS940 page


Hello Jeff,


Just writing to say that I have found your 940 page most useful in repairing a couple of units here. One which suffered a terrible overvoltage surge and another with strange digital B unit problems. Your pages are invaluable as a source of information and links to other information.


In viewing your page I couldn't help but notice the 940 brochure is for a Trio unit, the same as I have on my website at I was also interested to note that it has the original Lowe Electronics UK stamp on it, the same as mine and even the same scuff marks and folds. Seems rather likely that it might have come to you by way of my site, have a look and see what you think.  [Editors Note: I confess I copied Martin’s brochure, and he is ok with the copy.]


I also have on my site the code for the TS940 and the computer interface EPROM's should anybody ever need this to either replace or reproduce them, I don't believe this information is available elsewhere. You can also find the documentation for the IF-232C and the somewhat rarer IF-10B together with all of the various programming data. [Editors Note: Now in the links section: It is the original TS-940 page]


In repairing the 940 that suffered a nasty overvoltage I found that in addition tho the usual zener and driver transistor failures that the zener, D1, on the PA board had also failed short circuit. I still have a problem with the LCD display on this rig which I am working on now. It seems to have the top row illuminated but all segment dots are on, never seen this one before.

Keep up the good work,



Martin, HS0ZED, G4UQF






From: Edwin Bruijns []
Sent: Tuesday, 11 July 2006 8:54 a.m.
Subject: ts940s


Dear Jeff,


My name is Edwin Bruijns, PA7EW from the Netherlands.

I recently bought an old TS940s, and via Internet I found your TS940 site with info about mods etc. First I would like to compliment you with this nice initiative and the info about the TS940 . I changed the two fets and found a small improvement in receive (on the ears). Now I followed the discussion about the two resistors R149 en R150. But it is not so easy to find a good conclusion. Am I right when the info from KI4NR (John) concluded that we better not swap te resistors (in other words, the actual placement of the resistors in de print is correct). And what is your conclusion about this advise. I thougt, better ask then try with some error-risk on other parts of my beloved TRX.

I hope you can give me some advise,

Thanks and 73's to you and your family.

from Edwin the PA7EW

QTH : Hoorn 35 km north of Amsterdam.



From: Gerwitz, Jim-P06288 []
Sent: Monday, 21 August 2006 10:26 a.m.
Subject: RE: TS-940 CD


Thanks Jeff…!  Have a great day!  Your web site is great!







Back to Part 1 of TS-940 page: Click here





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