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TS-940S Production Errors Found

from Nelson Ricardo - PY1NR on September 27, 2004
View comments about this article!

Some corrections that will significantly improve the already very famous TS-940S receiving performance

This article is dedicated to the "detail" lovers

Are you a Kenwood TS-940 owner? You should know that it could be even better if you do some minor "corrections". Two errors that I found and are also showed in the Service Manual, Revised Edition.
All photos and pictures are available at:

I can assume that thousands of other TS-940 are also waiting to be corrected and perform a receiving even better (mistakes "hidden" for more than 20 years!)
Check yourself with instruments; it's more than 20 dB of gain and a better AGC performance.

See the Level Diagram in the Service Manual. With the FETs right position, we would have 12.5 dB gain in the RF Preamp, and 17 dB in the 2nd balanced mixer.

I laugh a lot when I confirmed both errors! Many decades waiting to be corrected! As I never heard about this problem, I decided to reveal it to the whole world. My radio was working apparently well, where this is the 1st TS-940 that I could observe and analyze in detail its circuits. First I found the RF Preamp FET in an odd position, but only few days after I could focus and see that the cascade circuit was correct in the schematic diagram and wrong in the PC board. It was also wrong in the PC board views in the Service Manual.

I also noticed that a FET was hotter than the other. It was as simple as un-soldered and turn the FET 180° and re-solder it all over again.

The RF gain increased and the noise decreased. -- Very fine! But, in the middle of the night, excited with this amazing discovery, I kept on thinking if this error was the only one.

I got back to the Service Manual, and following the circuit diagram, checking the PC boards, I found a second "mouse": in the 2nd balanced mixer, in the IF unit, another inverted FET (Q4), harming the mixing/conversion, the gain, and the AGC performance.

By eliminating these "losses", my famous TS-940 "won" 10 dB more! I suggest you to revise the famous TS-940 receiving performance to be even better, of course!

Have fun revise your TS-940! Smile!
Nelson Ricardo - PY1NR

Member Comments:
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TS-940S Production Errors Found  
by AL2I on September 27, 2004 Mail this to a friend!
Very sweet find Nelson! Kenwood is a typical manufacturer: I wonder what other rigs are passing factory QC with something that is not quite right. I hope yours was a highly unusual case, but I suspect it is not.

TS-940S Production Errors Found  
by N4ZOU on September 27, 2004 Mail this to a friend!
Very good ***** star article! We need more like this. Even if I do not have a TS-940 I might get one later so this gets burned to a reference CD for later use.
RE: TS-940S Production Errors Found  
by W8JI on September 27, 2004 Mail this to a friend!
That sounds like it was engineered OK since the schematic is correct, but someone made a mistake converting the design to production.

You be suprised how many new radios have built in design or production problems. It amazes me people put up with the quality of transmitters/receivers today.

Good work on finding this one!

73 Tom
RE: TS-940S Production Errors Found  
by N6AJR on September 27, 2004 Mail this to a friend!
superb article
TS-940S Production Errors Found  
by WA2JJH on September 28, 2004 Mail this to a friend!
good looking out.

Gee wiz, if this was done for every rig!!!!!!!!!!

The only radio you would not have to do.........
would be the EICO-753. It is such a POS, the whole rig is production errors engineered in!

Getting real.....

The DRAKE TR-7 has a transformer for a 25 V voltage reg/inverter. Every TR-7 I have fixed, the core broke off the transformer.

The TR-7A actually soldered on a wire loop to hold the transformer core together.

The TS-850. I guess everybody knows they messed up with NB1 and 2. However one simply has to change 2 capacitor values.

The GENAVE VHF H-T. Not enough trimmer cap for xtals.
You must put in 10pf caps to get the transmit frequency
within a KC or so. Otherwise your TX is off by 3khz or more!

TS-520S. the front end mosfet blows out. I guess they should have done something about bleeding off static build ups.

The Argonaught 509--$^*&^)^(&&%%$& DAIL STRING SYSTEM.


FT-100D &(^(^(%*&)% HF and VHF/UHF antenna connectors.
The mic you are stuck with. It uses the same wire telephones do. Ya know the frail wire mixed with cotton!!!!. ALSO ULTRA IMPORTANT----tHE FACE PLATE FALLS OFF TOO EASY!


TR-7 if you have an S/N below 3000, you may find a quick way to get the VFO more stable. THEY did not use real coax in 2 places. Check the web. You will see the pictures.

Those are a few that came from my experience.

I am sure everybody found something on one rig or another? Lets share?
TS-940S Production Errors Found  
by WA2JJH on September 28, 2004 Mail this to a friend!
One other. The Harris 350 aka 1446U mil spec varient

There simply is no easy or cost effective way to make this mil. spec beauty work well for ham radio.

YOU ARE STUCK tuning in either 10hz or 100hz steps.
It will take 5 minutes to go through 500KC!!!!
The RS-232 board is hard to find. You will still have to write your own machine code subroutine to get it to interface with a PC. Perhaps then you could use the rig blaster software package to have a real VFO on your computer screen.

COST. It has the best RX I have ever used.
Outputs 150W ultra cleanly. The CPU controlled speech proc and ALC optimisation,a pre-curser to DSP
This radio looks like it should be on the space shuttle.

Production errors-none, EXCEPT FOR NO VFO!!!!!
Sorry for the rant and rave! I love this 1986 RIG.
The VFO in MY Harris RF-3200 is a poor design. However it is also the band switch!
RE: TS-940S Production Errors Found  
by N4LQ on September 28, 2004 Mail this to a friend!
Here's a copy of an Email I sent to the TenTec reflector in 1999 about a Century 22 error. Even U.S. built gear has mistakes!

Sent: Tuesday, March 02, 1999 3:22 PM
Subject: [TenTec] Century 22 Error

Recently I acquired a nice Century 22. This rig uses an audio filter between
the detector and audio amplifier for all of it's selectivity. When I
advanced the "filter" control for maximum selectivity, I noticed that the
peaked or resonant frequency of the filter was very low, around 350hz. This
did not correspond to the manual's specification of 750hz and made for
uncomfortable listening.

Check the schematic of the RCVR/CONTROL ASSEMBLY and observe the 4 pole
audio filter across the top. Mine shows an LM3900 with 8 capacitors, all
being .0033uf. This seemed strange since the Delta 580 and Omni D use the
same component values yet the capacitors are all .0022uf. The ARRL Handbook
also indicates the caps should all be .0022uf. Now to see what was really
inside the rig. Sure enought, .0033uf!

I removed all 8 capacitors and replaced them with .0022uf. Now the filter
peaks beautifully at 750hz. Turning the filter to max results in a clean
750hz tone on cw notes.

I would appreciate some feedback on this. What does your manual show and
what is actually in your rig? Do other C22's have the correct value?

73 Steve Ellington N4LQ

RE: TS-940S Production Errors Found  
by WU7X on September 28, 2004 Mail this to a friend!

Please tell me about the NB1/NB2 cap fix! I love my TS-850, but the noise blankers are a joke.

73 & DX,

Dale WU7X
TS-940S Production Errors Found  
by WA2JJH on September 28, 2004 Mail this to a friend!
OK The OM that wanted NB1-2 mod. fer TS-850.

I did that mod over 3 years ago. They may have a better mod plus this site has about 30 other ts-850 mods.

There are a few sources. Best way is to do a booleen search on GOGGLE



You should get at least 10 results.

The website with the Blue pages, I have found to be the best.

You will see 50 mods to choose from.
Scroll down and you will see NB1/2 mod.
All the diagrams are their. However The service manual
should be used too. The print is bigger.

I remember that mod. Do it very carefully. I had to remove a chip cap amd put in a tantalum cap. It is all there on a few websites.

The RCVR ant mod is worth doing. The mod to get the ATU to tune the RCVR is a good one too. The auto-track atu mod is very good.

I would recommend NOT doing the AM BDVST ATTEN mod.

The NB mod. is not recommended if after reading the entire mod, you do not feel cofortable going that deep into the rig.

All the warnings are there. Those site's nor I take any responsibility if you damage your radio.

The TS-850 is not the most service friendly rig.
Watch out for those crummy white flex cables!
Also watch out for the IF jumper cables. They break very easy.

I remember doing 6 mods at once. Took me hours to find a tiny cable that pulled out! My heart sunk when the radio had no RX audio. I re-traced my steps and found a pulled flexi cable!

I would highly recommend you print up the entire mod/mods on to paper. Set your printer driver to magnify by 200%.

Sorry, if I made it sound more complicated then it is. I just do not want you to experience all the problems I had doing the mods.

It is worth the 2-3 hours to do. You will have noise blankers that really work! Funny, I heard the NB's on the TS-850, TS-950, and TS-450 are identical!
The TS-850 is identical to the TS-950, except for those caps you replace!!!!!!

Kenwoods official story was that NB2 was designed for long pulse noise. It was supposed to be engineered for the infamouse RUSSIAN WOOD PECKER QRM.
The Radio was designed during the near end of the cold war!!

If you like the TS-850 will really appreciate it after you do the important mods.

73 Hope my TS-850 will talk to your 850 in a QSO HI-HI
If you see another 850 for $700 or less, buy it!
The rigs link together without a computer.
You will then have dual recieve. Many rigs that have dual RCVR cost over $3000!

Please be advised that you cannot get certain parts for the 850. I blew out the frgile TX/RX relay board.

If you get lemons, make lemonaide! I took one of my TS-850's and removed the final box and ATU.
This gives me room for 8 D cells.

YUP, I am building a QRP version of the TS-850.
3-5 W class A amp. I will use the spare parts to build
a small filter for QRP TX.

Not too sure many people will want to read the process. I will probably not publish it!

RE: TS-940S Production Errors Found  
by W8DPC on September 28, 2004 Mail this to a friend! takes you to a webpage selling spyware protection. I thought you made a typo, but you did it twice.

You mean I think most people realized that, though.
RE: TS-940S Production Errors Found  
by K8LEA on September 28, 2004 Mail this to a friend!
Couple of sillies....

I once bought a Regency "Transcan" - about twenty watts on 2M with an 8-channel scanning receiver.

The transmitter had been screwdrivered to about a half watt (easy), but the receiver was barely there at all.

After ordering a manual, I noticed that a transistor on the receiver board had one leg sticking off to the side, and nowhere near the board.

That was "it".... It probably passed the "does it hear anything" QC test, but that was about all it could do. Maybe that's why it was so cheap, but I'm not sure how it could have been "in use" for better than ten years unless it never left a very good antenna.

I also built a Heath TV once that had two ways to wire the degaussing coil, depending on whether you looked at the instructions or the schematic. I guessed wrong....

NBD to fix it except that the primary failure was a power transistor inside a "sealed" HV supply. What were they thinking?

Probably about 1980, IBM built a run of 5211 printers (400 LPM, about the size of a chest freezer) that would implement the famous "HCF" instruction. That's "Halt and Catch Fire." Seems that there were two ways to mount one of the transformers on a power supply board, and one was wrong. The design was such that the thing worked perfectly, but the transformer got _very_ warm....

Stuff happens....

TS-940S Production Errors Found  
by WA2JJH on September 28, 2004 Mail this to a friend!
SRI ABT double TYPO. I would never misdirect someone like that. I think most people know that antispyware software you DOWNLOAD could have spyware in it!
Free-antispyware is the worst!

The DRAKE MUSEUM has mods. You will also see mil spec varients of the TR-7/R7A as well as the TR-8.

The TR-7 neeeds much improvement with the PTO.
The TR-8(never came out) was a TR-7 with a DDS VFO.
This other company makes digital replacement VFO's for Drakes and Collins. You will never see the VFO-75 which was DDS by Drake for under $500!

These after market DDS VFO's cost about $250. You get 20 memories and a computer interface!
YUP you can make the old collectables into a PC control
I might get one for my TR-7/R7A combo.

If you do not want computer control or TCXO accuracy, VFO stabilizer boards can be had for under 50 dollars. The drift is reduced down to 100hz/hr.
RE: TS-940S Production Errors Found  
by VE3ZXQ on September 29, 2004 Mail this to a friend!
Actually, two "free antispyware" w/ free updates I use all the time to help others to get rid of bugs!!

Spybot Search & Destroy is the best...look it up

Spywareblaster is the second one....

believe you me, you want these one in your arsenal..

take care..
RE: TS-940S Production Errors Found  
by VE3TJD on September 29, 2004 Mail this to a friend!
This goes out to WA2JJH specifically, as he doesn't have an email address listed.

Michael: Do you by any chance have a copy of the firmware within the eprom (27256 and IC18 I think, it's been a while since I've had it apart) for the 850? I have one that will start transmitting within any of the ham bands without pushing the PTT (yes, vox and tx are off!).

Outside of the ham bands, the RX works well. It hasn't been modified for out-of-band TX, which makes me think it's a software/firmware problem.

Thanks, Tedd
TS-940S Production Errors Found  
by WA2JJH on September 29, 2004 Mail this to a friend!
ZXQ, I had an utra bad experience with the free version of spybot. I also had an experience 7 years ago. IT IS FUNNY AS HECK IN RETROSPECT!

I edit digital video tape. I had one of the first non avid real time systems back then.

I go on the net to get a software upgrade for the video editor. I fell for an old trick! There was the companies site for version 1.1. There was a legitamate
ooking site that had rev 1.1A. It gets really freaky here! I swear you cannot make this stuff up!!!!!!!!

I had stupidy was using a free trial version of an anti-virus program that AOL offered free because AOL's mainframe got hacked! The antivirus was hacked!
So I really had no protection.

Anyway I download the video editing software UPDATE.

1) Two cartoon characters appeated on my screen.
2)The Morph into a "F" Finger. (getting the bird)

I cannot understand why people with such extreme programming talent, waste thier time in writting such a customised virus. Most peope did not have personal fire walls back then. I have a fire wall that tracks the sender of any sub 7 backdoor trojan virus JAVA-terror, and other crap on the net.

I am not saying your free sbybot is no good. However did you notice hen you downloaded it, it said use at your own risk!

I have my firewall set to max. I log about 50 spyware
and remote host events a day!
Most plug ins and active X is harmless. Spyware can be harmess too. The two big corps being sued are and www.

9 out of 10 PC's have double cick or alexa on thier c drives. These 2 corps are the dudes that get your screen name for spam. It is grey letter law as to how egal it is. Check out double cicks website(at your own risk)
They claim that monitoring browsing habits is a respectabe business. They claim the joint action law suite is bogus and violates their civi rights. They make a point of how many jobs will be lost, if they have to pay out the billions in punitive damages.

The OM with the TS-850 problem. I also had a TX lock up problem with an 850 I baught cheap.

The real expert on the TS-850 is Cliff from AAVID
Cliff no longer repairs radio's. However if you go to the product reviews, you can find Ciffs email.
Cliff might answer your question. He may not. He gets his brain picked by many.

If he is in a good mood, he will diagnose your radio on the phone! Yes he is that good. He is retired but still said he would answer questions.
I would email once. See if he responds. He can be gruff on a bad day.
Also be advised pacific parts is not stocking too much TS-850 parts. So buy what parts you need now. KENWOOD NO LONGER STOCKS MANY TS-850 PARTS EITHER.

73 mike
RE: TS-940S Production Errors Found  
by K0RFD on September 30, 2004 Mail this to a friend!
Cliff from Avvid certainly is a resource.

But he's retired and we should respect that.

In his retirement announcement, he said that he would continue to monitor and post to the Kenwood mailing list.

That's more passive. He can read the list when he wants to. Besides, somebody else might be able to answer your question. The Kenwood list is at:
TS-940S Production Errors Found  
by WA2JJH on September 30, 2004 Mail this to a friend!
VE3TJD, I hope this helps because I HAD THE IDENTICAL
PROBLEM! It may not be a firmware problem. If you did the hidden check sum test, and it said you did have EEPROM problems.........DO NOT READ FURTHER!

i GOT A ts-850sat AT THE tIMONIUM HAMFEST. It was sold to me for like $300! The guy did day it worked the last time I used it. I have been around long enough to know what that really means.

It means a few things. 1)The rig will not have all the features working to this radio was used as a tea bag in salt water!

2)At the price your getting it at, there is an understanding that you wil not bother the dude at the next hamfest if the radio is F.U.B.A.R!!!!!

It was worth a $360 gamble...right? IT WAS.

The AGC was broken. Some dude expanded the radio's TX
It was aligned with the infamouse ""GOLDEN SCREW DRIVER""
TRIVIA: A golden screw driver is usually a "GREENY"
The greenie is the small all perpose screw driver with the green handle. It makes it a crummy tool for trimmer caps and hexaganal ferrite slugs in IF cans.
You can aso open and close the rig with it!
It is customary to wear your greenie in your shirt pocket!

I spent about 6 hours fixing the rig. The 4 way AGC was now only off and medium. It had a few other small bugs I could not fix(NO SERVICE MANUAL).
However I also did a few mods. The NB1/NB2 fix. The ATU RX mod. A few others I found on the net.
Of course when all was said and done, the rig was more messed up! However I found it was simply one of those horrible cheapo flexi-cables pulled out. I also damaged an IF mini-coax. Simple resolder job.

To make a long story short, the rig worked great with furious round the clock operation.
On day on 20M, I am in a QSO and my power level starts to drop. I was down to 20W. I released the PTT.
Yanked the power cable. I did not 73 the OM, needess to say.

Turned the radio on and off 10 times. Hit CPU reset.
Then I cursed like a drunken sailor on the 4th of JULY!!!

I called CLIFF at AVVID. He described which parts burned out on the phone! This guy was THE best KENWOOD repair engineer in the US.
You see those little phenolic boards with SMT's on them. Their are about 10 in the TS-850SAT.
If you have the service manual, there is one that controls the TX/RX line.

Cliff simply replaced the miniboard. He also relaced the dried out electrolytics for the AGC. He aso aigned the radio to factory spec. He charged $151 that incuded postage back to me. I had to pay $60 to get the rig triple boxed and shipped.

CIIFF is no longer in business. This dude is an ACE!
He said he still might do consulting. You coud try emailing him. DO NOT DROP MY NAME OR CALL, I only USED HIM ONCE!

I like the TS-850 so much, I just purchased another one on ebay for $700 with some filters and service manual thrown in the deal. My orignal TS-850, the ATU blew. The TX/RX relay board get fried by lightening. The lightning protector worked!!! The TX and RX still works. However the TX/RX relay board is toasted! Kenwood no longer makes the tiny TX/RX relay board! It did save the rest of the rig.

*******ANOTHER DESIGN FLAW FOUND***************
iF YOU have a TS-850, you should beef up
the lightening protection.

Since Cliff is no longer in business I am in the process of designing that $360 TS-850 into either a QRP version of the 850. Build external TX/RX relay.
Remove final. Use a minicicuits $1.99 class A 100mw amplifier chip, Use a $5.00 low pass and bandpass miniciruits filter 3-30mhz on the input of the 100mw amp. Then use a cable TV power brick to get 5W. Follow with triple cascaded BP and lp filters.
Once you remove the ATU and 100W final, there is enough room to put in 8 D cells and a QRP AMP and TX output filter. I will hve to do something about the high drain flouresent dispay. Perhaps put in a capacitive sensitive panel. The panel will only
light, when the rig is touched. Just an idea. I may keep it for parts for the other TS-850sat. I have a feeing there will be few parts around for this excellent rig.

Either that or get all the IF filters and make it a great RX!

So go on the net. You should find the CHECK-SUM test for the EEPROMS.

Hope I was of any help....73 MIKE
TS-940S Production Errors Found  
by WA2JJH on September 30, 2004 Mail this to a friend!
K0RFD YOU ARE RIGHT! CIFF PAID HIS DUES! Hams should read all the extra things he did, and never charged!

Cliff is an impossible act to follow. If you read the reviews, many will say he was almost psychic.
If you had a Kenwood, you gave him the symptoms, he would tell you on the phone what was bad.

I hope not to many low lifes called him, got a diagnosis. If the repair was easy Cliff got gypped!!!

Is that why he is retired? His rates were dirt cheap!
a typical HF radio....about $150. H-T's perhaps $40 tops!

Also he got soo popular, 80% of the time if you did not have the radio back in a few weeks, it was because
50 rigs were ahead of yours!

SRI PSE DO NOT BOTHER CLIFF. SRI, I gave out the info.

Perhaps he can spend time on the air. I would love to rag chew about the innards of KENWOODS.with Cliff.
I bet he has some really cool mods.

He should write a book of KENWOOD and ICOM repair.
I am sure it would sell well.

Honest as ABE. He would also spend lots of time with you on the phone. He would answer questions that had nothing to do with your repair.

I am sure he likes being retired.
K0RFD, if you talk to him, tell him Mike from NYC wish's him well.

RE: TS-940S Production Errors Found  
by W1CC on October 2, 2004 Mail this to a friend!
A very interesting article indeed. I have a late model TS-940S (10 million serial number) and I recall that Kenwood had (or has) a practice of making making continous production changes in its radios. Before I open my '940 up to check for these reversed FETs, I am wondering if anyone else has found this same problem in their '940 and what the serial number is on the radio? It would be interesting to see if this problems was "fixed" in production like so many other early '940 problems.


Tom, W1CC
RE: TS-940S Production Errors Found  
by W1CC on October 2, 2004 Mail this to a friend!
A very interesting article indeed. I have a late model TS-940S (10 million serial number) and I recall that Kenwood had (or has) a practice of making making continous production changes in its radios. Before I open my '940 up to check for these reversed FETs, I am wondering if anyone else has found this same problem in their '940 and what the serial number is on the radio? It would be interesting to see if this problems was "fixed" in production like so many other early '940 problems.


Tom, W1CC
RE: TS-940S Production Errors Found  
by W1CC on October 2, 2004 Mail this to a friend!
A very interesting article indeed. I have a late model TS-940S (10 million serial number) and I recall that Kenwood had (or has) a practice of making making continous production changes in its radios. Before I open my '940 up to check for these reversed FETs, I am wondering if anyone else has found this same problem in their '940 and what the serial number is on the radio? It would be interesting to see if this problems was "fixed" in production like so many other early '940 problems.


Tom, W1CC
TS-940S Production Errors Found  
by WA2JJH on October 2, 2004 Mail this to a friend!
Nelson I agree it is worth it. You know the AIP or some rigs allow you to kick out the pre-amp.
By doing so you loss 10db.

I bet you can kick out the pre-amp have .25uv sensitivity and you will have no intermod and noise from the pre-amp.

Better rigs do use a pre-ampless front end because they did what you did. The pre-amp bypass or AIP was always a joke on all kenwood rigs. So your mod was worth it, big time.

The Drake TR-7 does not have any pre-amp at all. Yet the TR- is considered a sensitive quiet RX.
They mimimised every loss in the chain they could.

The real proof will be if you either bypass the pre-amp or use the AIP. I forgot if the 940 had AIP or pre-amp out. What ever operate the RX with far less noise is what will happen.

There is a mod on the TR-7 in the 1st IF. The DBM is old. It is made by a conmpany called Vari-L.

The mod is to replace the DBM with one from miniciruits. The result is even beter RCVR sensitivity.

You posed the most important question....Is it worth it.

When I look at a mod, I see how deep I have to go inside the rig. The NB1/NB2 mod was worth it.
The 940 and the 850 have the ssme schematic on NB1/NB2

The designers of the TS-850 thuaght they could modidy the 940 NB to get rid of :THE RUSSIAN WOOD PECKER: The result was a medecre NB1 and a NB2 that was good only on long pulse noise.
Well no more wood pecker. TS-850 users found that NB-2 had to be turned off. If you did not the RCVR would blsnk out every couple of seconds.

The BIGGIST MISTAKE. The TS-850 came from the factory
to be able to transmit from 27.475-29.999!!!!!!!
WOW a deluxe freeband radio! The only reason I could come up with.

The so called MARS/CAP mod is very dangerous to do.
The entire radio has to be disassemled to get in front off. 2 SMT diodes ahve to be swapped.
You could mess up the CPU or firmware.

So maybe kenwood gave in to having 10.5 meters ready to go! They did not want anybody doing the MARS?cap mod. Check it out on the net. You will see how bad the mod is to do! A freebander would break the radio.

Sometimes a mistake works to you advantage. There is a hidden menu code that allow to to manually adjust the ATU tuning caps. You use the VFO knob and the memory rotator switch to control the moters that tune the ATU caps.
OK, sorry to have dominated your post. I have a TEN TEC pegasus that has not been opened by me. I want to see the inside consruction.

Since your computer has all the lights and knobs for this vitual rig. Perhaps I can put 8 lithium batts in there for QRP field use. Also want to see if I can build get a 3kc wide roofing filter.

73 mike
RE: TS-940S Production Errors Found  
by VE3TJD on October 3, 2004 Mail this to a friend!
>It may not be a firmware problem. If you did the hidden >check sum test, and it said you did have EEPROM >problems.........DO NOT READ FURTHER!

Hi Mike: Could you please tell me how to do this test? I don't have the owners/service manual (yet).

Thanks, Tedd
RE: TS-940S Production Errors Found  
by C6ANI on October 3, 2004 Mail this to a friend!
Would be most grateful to establish contact with WA2JJH with respect to his posting relative to the TR-7 and its drifting. I can be reached at
TS-940S Production Errors Found  
by WA2JJH on October 3, 2004 Mail this to a friend!
There are a few menu's that pop up while holding down a key while you power the TS-850 up. I do not remember every mod in my head.

simple go to your favorite seach engine and do a booleen search

Search kenwoood TS-850+MOD. You will get the sites that have the checksum test and every other mod.

This works for any radio.

Many rigs have hidden menues! The process is to hold down a few keys while turning the radio on!.

Good luck with your ts-850. One of the last decent rigs kenwood made.
RE: TS-940S Production Errors Found  
by WA2JJH on October 3, 2004 Mail this to a friend!
OK, I heard someone was looking for me. I sent you an email address that I check fairly often.

TS-940S Production Errors Found  
by WA2JJH on October 4, 2004 Mail this to a friend!
This mod solves the TS-850S noise blanker problem in eliminating electrical interference and makes the nb design the same as the ts940 which doesn't have this problem. Results are outstanding. For the sceptical; Its easy to reverse mod.

The NB board reference is X59-1100-00 and it is located directly under the radio speaker.Remove the upper part of the cabinet and unplug the loud speaker. You will have to remove 4 screws and unplug 3 connectors in order to extract the board.

The picture here shows the board mods required.

The capacitors to isolate are C618 and C619

Taken from DKMOD

TS-940S Production Errors Found  
by WA2JJH on October 4, 2004 Mail this to a friend!
ve3tjd...This is one thing I got in a few secons with an enhanced booleen search.

Additional Front Panel Functions
Pressing SCAN + TX-M.CH will set the radio into its extended
function mode. These options can be scrolled via the M.CH/VFO CH.
switch. The following are the extended functions:

00 - This is the ROM Checksum displayed as a 4-digit hexadecimal
number This cannot be changed.
01 - Allow filter selection in transmit. Initially set OFF.
02 - Antenna tuner power down. Initially set to OFF.
03 - Antenna tuner non-stop mode. When set to on, the antenna
tuner will not stop when the lowest VSWR is found. Initially
set to OFF.
04 - Store mode, and filter settings prior to changing bands, or
channels. Initially set to ON.
05 - Display -HELLO- on digitial display, and send it in Morse
code on power up. Initially set OFF.
06 - Turn full LCD display ON on power on. Initially set OFF.
07 - Turn Subtone ON or OFF. Initially set ON. Note that even
when set off, the TONE indicator will be lit on the display.
08 - Unknown. Initially set OFF.
Note: I haven't tried or verified any of this, proceed at your own
risk. And do not transmit outside of legal bands. WA2ISE
Thanks to those involved above.

A booleeen search is a fancy way of saying you added a "+ "join the subject matter together.

like TS-850+inrad filter mod.

A booleeen search will work with any radio.
TS-940+poor RX sense. Now the authers artical pops up from eham!

This is an important point. A few times the info can be false. NOTHING ON THE NET IS CHECKED FOR ACCURACY!!!!
TS-940S Production Errors Found  
by WA2JJH on October 4, 2004 Mail this to a friend!
ok,I need a little help. I just got another used TS-850. today

BEFORE I GO NUTSO(some have said I am a nut anyway, but a good but)maybe someone had this exact problem.
I do have a junker 850 for parts.

The radio worked fiine out of the box. After a few CQ's, the TX locked up.

Turned the radio off and on a few times. I have not done any menu majic yet.


nO tx OUTPUT.....aNY IDEA'S?




TS-940S Production Errors Found  
by WA2JJH on October 4, 2004 Mail this to a friend!
this is instant barma (: < ! My cat diedn on the date,
I won thw radio !npass the PROZAC!_
RE: TS-940S Production Errors Found  
by KG5JJ on October 4, 2004 Mail this to a friend!
I've owned nearly all of Kenwood's HF line starting with the 520 through the 2000. Want to hear an ironic fact? I had trouble out of all of them, including many problems with the 940, except TWO models. The 520 and the 2000.

If the old adage "something old is new again" rings true, the 2000, which has been flawless thus far, may have the rock-steady reliability of their 520.

I know there are always exceptions to every rule, and YMMV, but thought it odd that these two rigs have been so good to me.

73 KG5JJ (Mike)
TS-940S Production Errors Found  
by WA2JJH on October 6, 2004 Mail this to a friend!
If you use that simple search method,all sorts of design flaws will pop up on many rigs.

An easy one is to change the time costant in the ALC of a Drake TR-7.

The result is punchier audio. You are not affecting the ALC to prevent over drive. The attack and decay constants are cut by 1/3.
TS-940S Production Errors Found  
by VE2DC on October 6, 2004 Mail this to a friend!
Not only Kenwood. The IC781 had a problem with power overshoot due to ALC problems. The fix was to change parts around to match the schematic in the service manual!
TS-940S Production Errors Found  
by WA2JJH on October 10, 2004 Mail this to a friend!
WHEW...That KENWOOD TS-850 just had a loose cable.
Muh ham gear gets damaged by UPS. Seems like we all but our used rigs from ebay!

The dude with the TR-7. A Huff and Puff stabilser board sells for $75. It mounts near the VFO.

Now do I have old software for my pegasus oris the RX very broad? 1999 firmware. Can the Juiper RX SSB on the 500HZ filter!
TS-940S Production Errors Found  
by WA2JJH on October 10, 2004 Mail this to a friend!
S0rry neilson, if I seemed to hi-jack your thread.

Your TS-940 error was real detective work!

Is it just me, or does Q.C., sampling, feedback, and engineer design team re-evaluation not done at our rig makers.

Or is it us as experimenters and sticklers for detail make us find these faults?

I will not buy the first of anything(yes, steve you lucked out).

Neilson, do you intend to call Kenwood and tell them?

Seems like all the real classic modern rigs of the past, have not become the radio's they are at, when the production run ends!!!!

TS-850 is the "sister ship" to the TS-940.
THE TS-850 becomes an excellent radio after a few mods, 2 added filters, and re-engineering by hams like you.

1)NB2 mod
2)TX and RX tuned by tuner mod. Imagine, why not use the tuner as a preselect.
3)Not to mention all the improvements you make to the radio by exposing hidden menu's!

One mod allow you to manualy tune the VFO and VFO mem in manual for antenna tuning! It will memorize your settings. THESE ARE SETTINGS THE RIG WILL NOT GET IN AUTO MODE! I am going to try this n my HL-2200 AMP
Have a manual memory for 80M. Most solid state rigs will not tune into an old SB-221.

WB2WIK/6 you try that trick yet? If you did and it did not work, pse let me know!

Another OPTION/MOD is the tuner will track your tuning.

THE DUMBEST BLUNDER!!!! THE ANTENNA TUNER ONLY TUNES THE tx. Switch a few cables on the ATU. The RX must go through another set of band filters.
Add the external receiver jack while your inside. See if that glass tube on the TX/RX relay board is ok. That is your lighening protection!

Should that glass tube be blown, you have no protection for static discharge. MANY RADIO'S ARE THE SAME WAY. Their should also be a GNDloop detector.

Seems to me, we are getting a slight taste of the ham biz!!!!
TS-940S Production Errors Found  
by WA2JJH on October 12, 2004 Mail this to a friend!

OK, you said you like details. I am designing a NEW from scratch pre-ampless front end for the TS-940 and the TS-850.

Many have added either RX only antenna connectors.
I know WB2WIK did the mod. To get the auto tuner to match match the RX front end.

This mod. Along with an ultra low loss minicircuits
band pass filter. The mod. will allow a few options.
Add a 3-30mhz bandpass filter from minicircuits.

I will have to add a few ultra low loss toggle switches and 3 SMA connectors. Sorry, it would be a real pain to install 3 s0-239's. Simply buy a the SMA's
from Pasturnec or any other good RF store.

1) Flip one switch, you have TS-940 normal op. The ex option would be that the antenna tuner is in line with the RX front end in RX mod. The only limitation is that your TS-940/850 should have an antenna that can handle the 3:1 Max SWORE.

The bonus is that the tuner acts as a preselection for the RX.

2)Mode 2. a second switch will add a 3-30MHZ bandpass filter. Minicircuits charges 2 dollars for a 50 ohm in/out low loss, shielded multi stage LC filter.
This and the in-line antenna tuner will not let all sorts of crap entering. The BPF is directional. This will isolate any unwanted IMOD. The 50 OHM match is preserved.

I also did the NB2/nb1 cap mod on the TS-850's MIS-designed noise blanker. I got dramatic noise reduction.
I kicked in the tuner and 3-30MHZ BPF. All sorts of 60 and 120 Hz noise gone! Lots of birdies eliminated too!
The BPF inside the radio got rid of all sorts of junk!

It is deep inside the TS-850. I know have a problem.
static must have damaged the DDS or PLL. I will complain later. More modulating!!!

I want the front end of a DRAKE R-7A or TR-7.
The pre-ampless 1st mixer can be duplicated!!!!!
I have not built it yet. I have to fix the problem I created during the must need NB1-2 mod.

My Blanker perfoms ultra well now. Many wrote off the noise blanker. IT IS THE SAME Blanker AS THE TS-940.
They added two caps that ruined the blanking time constants.

With these two mods, my noise floor dropped greatly.
I would add the 1.8khz and 500Hz optional filters to the TS-940and TS-850 next.
I also found the high voltage inverter that powers the back light generates noise and consumes a lot of power!

OK...The grand finale. I am building it now. A pre-ampless R-7A/TR-7 front end! Anybody that used either radio knows what I mean! Sometimes there is such a low noise floor, you forgot the radio was on!(HI-HI)

Kentwood uses 2 separate pre-amps. MOSFETs will mix as well as amplify. With all the DDS's, CPU's, and a noisy 350KC voltage inverter............Even the frequency optimized separate pre-amps will get flack!

Drake did not use a pre-amp before the 1st mixer in the R-7A and TR-7.

I looked at the TS-850 schematic. Both the high and low frequency MOSFETS can be bypassed. I am not sure if I can pull this off.

Since we eliminated a lot of CPU, and Voltage inverter (more on that for QRP use!) NOISE, THROW TOGGLE SWITCH 3, AND BYPASS THE MOSFET PRE-AMPS!!!

The RX path is all done with mini-hardline!
Antenna, ATU to match the antenna, a 3-30MHZ filter, we may have just made up our loss of the MOSFET Pre-amps.

The only mixer trick to be done is to adjust the L.O. injection level to our mil spec. mixer.

Take the VHF L.O. freq spread. Put in a mnicircuits
BPF for the L.O. range. Amplify it with a 4 lead minicircuits small signal amp. Put the output of the amp and filter it again.(minicircuits makes a 50-75 mhz
BPF) Put the amps out put into a minicircuits 50 ohm matched variable attenutor. Use the more expensive $12.00 one that uses pin diodes and has a directional coupler on the output.

HOPE THIS WORKS! You have an option of KENWOODS front end, or a highly filtered L.O. that can be optimized exactly to the first mixers MOSFET.

Another noise reduction trick. Vary the voltage to the high voltage inverter for LCD back light brightness
Why not try to use the pot that is for the TONE CONTROL. The tone control has minimal effect on RX tone anyway.

Set the pot up as a voltage divider for the HIV inverter. You can go from bright to off. Off would be great for QRP ops. Keep the volume low and use head phones. You should get a power drain on RX that will allow you to use these Kenwood rigs for QRP!!!!!!!

Sorry, If I bored you guys.

If anybody can tell me what is wrong with my TS-850.
No RX/TX The frequency display turns to all dots.

I suspect the DDS oscillator board.
I get no TX or RX. The frequency is displayed. It then flashes to a series of dots. Any idea's? HELP!!!!


Imagine a TS-940/850 that has an RX as good or better than a TR-7 or R-7A. The rig will have a 5W
QRP mode to boot!!!!!

If I can get it to draw 1 AMP Max on TX and RX, one would have a full featured QRP rig!!!

Please feel free to point out any engineering flaws.
I like to redesign my radio's

What do you OMs think? If I fix this radio, I will do every mod I can find.

Ohh it seems DSP is all the rage. I guess I could add
every AUDIO DSP inexpensively. DNR, DSP speech proc. and perhaps DSP Audio eq.


73 DE MIKE (:
TS-940S Production Errors Found  
by KE5RI on October 25, 2004 Mail this to a friend!
Nice detective/engineering work, Nelson. I did not make before and after measurements but I noticed the obvious improvement. The whole correction took me about thirty minutes. Thanks for the great tip.
RE: TS-940S Production Errors Found  
by ZL4AI on December 13, 2004 Mail this to a friend!
After carefully going over the circuit diagrams, I cannot understand how these transistors are around the wrong way! There does not seem to be any logical explanation in the article as to how it was determined the transisters are incorrectly aligned. The schematic diagram is not at all clear, and does not show the alignment of the transitors at all. Both transitors could be turned around in either direction. My reading of the circuit diagram which is also in the service manual shows that the trasistors are correctly positioned. Can someone please explain how it can be determined that these transistors are around the wrong way?

Yours sincerly
Jeff ZL4AI
RE: TS-940S Production Errors Found  
by ZL4AI on December 18, 2004 Mail this to a friend!
My statement in the previous post is incorrect:

In the service manual, transistor “Q4 on the IF board” and transistor “ ‘Q10 lower’ on RF board “ are shown:
- (correctly) arranged in the Kenwood circuit diagrams.
- the reverse way around on drawings of ‘components on the circuit board’,

To prove this to yourself:

Starting with Kenwood’s drawings of ‘components on the circuit board’, reverse engineer out the circuit diagrams.
Do this by interpreting the layout of components from the board and redrawing out the circuit diagrams.

You will find the only way you can produce the Kenwood circuit diagrams, is to swap the D @ S leads (as Nelson has recommended).

Presumably Kenwood’s circuit diagrams are originally correct.
If the circuit diagrams are correct then the transistors must be then wrong way around on the boards.

This approach following the conventions that Kenwood set down in the manual.

Jeff ZL4AI
RE: TS-940S Production Errors Found  
by KE5RI on December 18, 2004 Mail this to a friend!
I called Kenwood the other day to ask them what they knew about the FET errors. I was told that they had heard something about this but as the tech remembered, the FETS were installed correctly. I asked him to please check with their engineers again and to please get back with me for confirmation. Nothing heard yet. I will post additional info if I receive it.

RE: TS-940S Production Errors Found  
by W1NR on April 12, 2005 Mail this to a friend!
This was discussed at some length on the Kenwood reflector. The answer from Kenwood was that the SCHEMATIC is incorrect. Swapping the FET's may appear to give you a gain increase, but destroys the noise floor and weak signal response in the process. In other words "It ain't broke so don't try and fix it!"
RE: TS-940S Production Errors Found  
by ZL4AI on April 12, 2005 Mail this to a friend!
Full details of Kenwood's replys and advice can be found on the TS-940 home page.

There is also full information there about how to fix a new recently discovered and even more sigificanat production mistake in the AGC timing. Fixing the AGC significantly improves receiver performance.
RE: TS-940S Production Errors Found  
by W4VD on April 15, 2005 Mail this to a friend!
I have one of those solid state rigs you say have trouble with the SB220, I have had 2 before and ran solid state with no problem *ts 930 and 940* but with an Alinco DX80TH I simply cannot drive it, I was thinking the inputs hadn't been aligned, but I would like more info on that if you would be so kind as to post it, or e-mail me at

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