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Improve TS-940 Receiver for Weak Signals

Jeff King (ZL4AI) on June 8, 2005
View comments about this article!

Improve TS-940 Receiver for Weak Signals

0x01 graphic

Incredible HF rig!
Now it's easy to modify a TS-940S to hear better (or as well as) a TS-950SDX.

When fixed, TS-940 really pulls out those very weak signals.
ZL4AI discovered a serious manufacturing oversight in the AGC timing.
Simply swapping 2 resistors around, enables this rig to hear as Kenwood designed and intended in Kenwoods original circuit diagram.

Full explanation details, photos and circuit drawings found on:

The error is on the IF board:
Kenwood printed labels for R149 and R150 around the wrong way!!!
As assembled by the factory, (the outcome is) in the main signal path, a 2,200 Kilo-Ohm resistor ends up where a 150 Kilo-Ohm Resistor should be. Being 14 times larger the 2,200 Kilo-Ohm resistor (incorrectly) significantly degrades the signal. Swap the resistors around and the receiver hearing improves significantly!!!

Kenwood have been really helpful and have confirmed the resistors are in the wrong place. Kenwoods emails are on:
Kenwoods dedication to customer service and improving equipment is very impressive!

Probably “these resistors in the wrong place” occurs in every TS-940S produced.

Copy right ZL4AI

Member Comments:
This article has expired. No more comments may be added.
Improve TS-940 Receiver for Weak Signals  
by WB2WIK on June 8, 2005 Mail this to a friend!
This is great!

Now, if only I hadn't sold my TS-940 in 1990 when I bought the TS-850.... :)

RE: Improve TS-940 Receiver for Weak Signals  
by K1DA on June 8, 2005 Mail this to a friend!
There is an AGC timing modification for the ICOM 721 723 725 726 728 and 729 series which was discussed
in a two part article in QST some years back which really makes the redios sound better. Transmit AGC timing was also changed for the better.

Improve TS-940 Receiver for Weak Signals  
by WA6BFH on June 8, 2005 Mail this to a friend!
Since I don't own a TS-940, though I did briefly bring up your link, would you mind 'bottom lining it' for me?

Is it an L.O. injection problem, or what?
RE: Improve TS-940 Receiver for Weak Signals  
by WA1RNE on June 8, 2005 Mail this to a friend!

Use the link


>> This is what the mod does:

Significantly improves the AGC timing function: After modification:

- You hear weak signals a lot better.

- S meter with AGC SLOW ON becomes quite responsive and lively in the region of S1 to S4 signals.

--Before S meter did not move much in S1 to S4 region.

--Before it would take a strong signal to lift the meter suddenly to S4

RE: Improve TS-940 Receiver for Weak Signals  
by K8MHZ on June 9, 2005 Mail this to a friend!
<Kenwood have been really helpful and have confirmed the resistors are in the wrong place.>

Let's see how helpful you think they are if you ever have to send a rig to them for repair!

I have had such terrible service from Kenwood that I am thinking that the only thing worse is their products.

Reading this article has enlightened me on Kenwood's quality control. Obviously something of this nature would have been would have been discovered at the factory if they just took the time to look.

I have three Kenwoods. A TM-241A that had a factory flawed display, the notorious junk Toshiba power module (I won't put a THIRD one in, the junk radio is now a FINE police scanner) and a factory defective mike. The radio was sent to Kenwood two or three times before I just gave up. They fixed the display and charged me royally but weren't smart enough to even be able to operate the radio. Either that or they were lying about the mike, which they said worked properly. I have a TM-V7A that is only 7 months old and as a factory flawed display (OOOH Deja VU!!) and a couple minor audio issues. I also have TS-520SE with a non working S meter. I bought it used at a yard sale in this condition. I knew it was not perfect, but the price was right. But the bottom line is that I have a brand name with a 100 percent defect rate and don't trust the factory repair folks based upon direct personal experience.

So, my motto has become "Kenwood....the best advertisement for Icom you can waste your money on!"

Really, to let a product out the door with such a glaring mistake as outlined in this post should be considered tragic, but it seems that it is status quo for Kenwood.

OK, I'm done now.


Mark K8MHZ
RE: Improve TS-940 Receiver for Weak Signals  
by NL7W on June 9, 2005 Mail this to a friend!

Just a little jaded, eh? Do you really feel your limited experience with selected new and used Kenwood products affords you "right" to scorch them? I suppose so; it is a free country. Your comments say much of your world, though. But really, do you think scenarios such as yours haven't happened to other consumers with differing brands? Do you think 20 and 30-year old equipment doesn't require maintenance and TLC once in awhile? Come on... what of your world - again?

Thank you Jeff King, ZL4AI, for taking time out of your day to put together a helpful post that improves upon an extremely popular rig from roughly two decades ago. Cudos - I'm sure this post will help those proud owners of this classic rig. Long live the 940Sat...


RE: Improve TS-940 Receiver for Weak Signals  
by W8DPC on June 9, 2005 Mail this to a friend!
"OK, I'm done now."

Soooo, you bought one Kenwood, it was junk, you bought a second one, IT was junk, so you went out and bought a third one?

Improve TS-940 Receiver for Weak Signals  
by ZL4AI on June 10, 2005 Mail this to a friend!
K8MHZ comments that this mistake was fundamental. I agree 100% Any reasonable form of quality review should have picked up such an obvious mistake. He / she is so correct. We are all completely astonished Kenwood did not pick up such.

KX8N comments are those of juvenile and undeveloped mind. Probably not worth further consideration. So you brought a commercialy marketed product and your name was David Crusan or something like that. Then you discovered the product was not to your satisfaction.
You should remember that America is the land of free enterprise and apple pie. So you will take an honest and objective review preared with great effort and try and impose your synical and and unhelpful comment, with just 2 minutes of effort. Really David your view is junk! which is of what you speak! You have an insincere way that is no use to us, as dedicated radio hams. Please can we have comments about the matter in hand and not David Crusan's frustrations.
RE: Improve TS-940 Receiver for Weak Signals  
by N2MG on June 10, 2005 Mail this to a friend!
There was apparently a "reversed FET" error (or series of them) discovered by a ham in PY land.

I wonder how these two "mods" play together...

Mike N2MG
RE: Improve TS-940 Receiver for Weak Signals  
by K8MHZ on June 10, 2005 Mail this to a friend!

I DO feel stupid for that. In fact, I bought my last Kenwood VERY reluctantly from ComDac. I told them of my experiences and they ASSURED me that Kenwood was a changed company and their products were now practically defect free. What a bunch of bunk. It was only about 3 weeks before the display started failing. Do a search (like I should have, again, I feel pretty stupid for buying the TM-V7A) on the problem they have been having with the blue display since day one. They try to tell the buyers that the new models (like mine) have been produced with an upgraded display that does not have problems. Well, at least their upgrade made the display fail within the warranty period, the old troublesome displays usually would not fail for at least a year.

Also, be aware that the first Kenwood I bought was a TS-520SE in very used condition. I had no expectation of perfection. The second was a TM-241A. That should have been the last one.


Jaded? I am not sure what you mean by that. I am 'scorching' them by telling the truth about their poor service and their poor products. They know about it too. The little snipe about them being a good advertisement for Icom was sent to them in writing the last time I corresponded with them. I got no response disputing my allegations.

Bear in mind that I also have Icoms and Yaesus that I use and treat very rough during ARES training, drills and events. My little FT-50R has bounced off the concrete so many times that I had to polish the scrapes off the display just to read it. It keeps on working. It routinely hits the ground so hard that it blows the battery pack off the back. Put it back on, and it just keeps working. My Icom IC-2100H has been in my Z-28 which rides like a truck, has T-tops that let all sorts of dust, pollen, some water and a leave or two get to it. No probs except a little SMT switch in the mike that needed to be re-soldered. The fix was quicker than packing it for shipping. It runs all day on high power without so much as a hiccup.

The TM-V7A has been handled with kid gloves and resides in my Caravan SE. It has never seen anything but TLC. Well, at least in the few months I have owned it, I did not see what was done to it at the factory.


Don’t be so hard on K8XN. Buying a third one after what I have been through does indeed sound ridiculous. I am going to have to put some of the blame on ComDac for their hard sell tactics. I know, caveat emptor, but the hams in the area are quite happy with the service they get from ComDac and I was comfortable (at the time) with trusting their statements.

The bottom line is that my experience with Kenwood seems to be indicative of the same caliber of the quality control effort depicted by the author of this thread. To let an entire line of products out the door with such an obvious mistake as a misprinted board is downright pathetic and to those with even an iota of a sense of humor it is laughable.

I am glad this article and the picture that is worth a thousand words made it to press.


Mark K8MHZ

Technical Reports+Excellant Customer Service Japan  
by ZL4AI on June 10, 2005 Mail this to a friend!
Fellow hams I am starting to comprehend something I did not know. There are some widespread concerns about some defects in some of Kenwoods equipment. I spend a lot of money getting my 940 believing it was a piece of high quality equipment. These resistors being round the wrong way has made me suspicious that it may not be as good as Kenwood’s marketing lead me to believe.
Hopefully some of the comments on this article will be on technical reports from other Hams as to how much they noticed a significant improvement when they swap R149 and R150. After PY1NR disclosed the FETs being around the wrong way, there were so many comments about some many defects on many other brands of radio, that the PY1NR article lost any meaning or relevance to a TS-940. I hope that does not happen here.

As for service. I have noticed substantial differences in attitude between countries. You will see on my website Kenwood Japan was VERY PROMPT AND COURTEOUS with their replies which were to the point, and helped by readily admitting the resistors were the wrong way round. EXCELLENT CUSTOMER SERVICE. If they denied it then this would have been much more difficult.
I also sent that same question to Kenwood Australia and Kenwood USA. Neither bothered to reply. That was disappointing.

An earlier question I sent direct to Kenwood USA was answered with: “You would have to approach your regional Kenwood Office”. Kenwood USA were very unhelpful and wasted my time over two emails. Not being sure who my regional office was, I approached Kenwood Australia, who eventually came two emails later with some information. I also asked Kenwood Japan who gave me fax and email address for Kenwoods agent in New Zealand. The email did not work, and the New Zealand agent never replied to the fax. Really unimpressive!

It seems the Kenwood Service Company cultures varies a lot between countries. From now on I will always ask Kenwood Japan directly. Heres the Head Office email:

I will not bother with Kenwood USA who made immediate effort to stop me asking, but made no effort at all to advise where I direct my question to. Maybe everyone should direct their questions to Kenwoods head office in Japan.
Improve TS-940 Receiver for Weak Signals  
by ZL4AI on June 10, 2005 Mail this to a friend!

The latest infomataion on on the FET reversals is on:

See the conclusions made by DF5KF.
It appears that reversing the FETs does not make a great deal of difference or any difference.
RE: Improve TS-940 Receiver for Weak Signals  
by W6IML on June 11, 2005 Mail this to a friend!
I agree with you about Kenwood's service record, which is horrible to say the very least! I sent my TS-940S to Kenwood for repairs on 01/09/2005, and now, 06/11/2005, Kenwood STILL HAS MY TS-940S!!! I phoned Kenwood and talked to the head tech, [Carlo] and he told me he would talk to his supervisor about getting my TS-940S fixed NOW, and get back with me in an hour. Well, 5 days later, no phone call. I'm about to go to that repair facility and sit in their waiting room untill my TS-940S is FIXED!
Any way I look at this, I will NEVER buy another Kenwood!
Dave W6IML
RE: Improve TS-940 Receiver for Weak Signals  
by WA2JJH on June 12, 2005 Mail this to a friend!
<<<<<<<Any way I look at this, I will NEVER buy another Kenwood
Dave W6IML>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

At this point in time,KENWOOD said they shall never
produce a new HF RIG.

Kenwoods run of glory started in 1976. The TS-520,and
the full featured TS-820. The TS-850 was the end of

Seems they no longer decided to be the head of the big 3.

TEN-TEC and ELEKRAFT now can take a market share.

I also see why KENWOOD always bragged about their tx audio. It seems the 940,ts-2000,and other KWs do not
brag about their TX OR RX!
RE: Improve TS-940 Receiver for Weak Signals  
by W6IML on June 12, 2005 Mail this to a friend!
"I also see why KENWOOD always bragged about their tx audio. It seems the 940,ts-2000,and other KWs do not
brag about their TX OR RX!"

Can't agree with you on this. Kenwood SSB audio is great in most all of their HF rigs, except the TS-570. The TS-870 I had always got great reports, as did every HF Kenwood I've had.
Are you sure Kenwood is no longer making HF rigs?
Improve TS-940 Receiver for Weak Signals  
by W8KX on June 13, 2005 Mail this to a friend!
Very interesting article. I owned a TS-940 for a short period in 1992 which I judged as having significant AGC problems, particularly on CW with the fast AGC setting. I knew several other hams who had terrible problems with reliability with the power devices in the driver stage.
Kenwood actually preplaced one ham's TS-940 with a TS-950 because of this issue. It seemed the last few production lots were particularly prone to QC problems.

I am concerned in general though about comments I see on eHam making broad brush judgements about a company based on individual experiences with specific radios. I can well understand the frustration and financial pain that a defective radio can cause but it doesn't form a statistical basis for judgements of this type. The TS-940 perhaps wasn't a high point for Kenwood but I've had many other KW product that were stellar and there have been dogs from all the major manufacturers.

More relevant is why the ARRL equipment reviews didn't catch a seemingly genetic problem of the type discussed in this article. The TS-940 review and ARRL reviews in general of that era sounded very much like manufacturer ad copy.
RE: Improve kENWOOD  
by WA2JJH on June 13, 2005 Mail this to a friend!
K6IML, Do not just take my word for it. There will be NO NEW BASE STATIONS!!

I found the DSP-100 can be duplicted.
RE: Improve kENWOOD  
by W6IML on June 13, 2005 Mail this to a friend!

"K6IML, Do not just take my word for it. There will be NO NEW BASE STATIONS!!

I found the DSP-100 can be duplicted."

My call is W6IML, not K6IML.

Well that sure is not a good thing for the Ham radio community!
Despite all the problems Kenwood has had with manufactuing defects, Kenwood has made some very impressive ham radios. I can think of several top shelf rigs that came from Kenwood from the 60's to now. The TS-520[S] and the TS-820S were solid performers with superb SSB transmit audio and fair recieve. The TS-830S and it's great speech processor, the TS-850S was a big seller for Kenwood, and I enjoyed the one I had very much. I sold it for close to what I paid for it, which is more than what I can say for all the Yaesu rigs I've had. The TS-870S was my favorite. It has the best recieve of any rig I've had up to [but not including]the JRC jst-245 I have now. [Best rig I've ever used!]
The last Kenwood I bought was a comment.
Maybe when DX is better [2 years from now] Kenwood will have a new HF rig out to compete with the mega-buck Yaesu's and Icom's. Let's hope so!
Improve TS-940 Receiver for Weak Signals  
by KC1MK on June 13, 2005 Mail this to a friend!
I've never owned a TS-940, so I can't speak from personal experience about this radio. However, I have owned two TS-440s and a TX-850. I had a minor problem (power output) with one TS-440. I used the TS-850 as my main rig for about six years, and it worked fine. Obviously this is just my personal experience and not a valid overall statement of Kenwood quality or lack thereof.
FWIW, I have also owned several Yaesus and ICOMs. I don't consider myself strongly biased for or against any of the big three. My current main rig is an ICOM IC-756ProII.
Jeff, KC1MK
RE: Improve kENWOOD  
by W0NCL on June 15, 2005 Mail this to a friend!
I guess the part I like best about threads like this is that people are still willing to get into their radios to experiment. Based on a lot of reviews I read here, I decided to get a 940. Its still a very nice radio. Its great to read about how something can be improved using newer and or better technology. Also, the amount of support across the internet is outstanding. 73 and thanks for the great comments.
Improve TS-940 Receiver for Weak Signals  
by KB9IV on July 23, 2005 Mail this to a friend!
Well I finally got around to the AGC mod. What a fantastic also improves CW to my ears. Inaddition the AGC mod also seems to improve useable weak sensitivity and decreases distortion.

Forget the "FET reverse" project. NO difference here, it's not worth the risk and time.

Best 73,

Bill KB9IV
Improve TS-940 Receiver for Weak Signals  
by ZL4AI on August 3, 2005 Mail this to a friend!

STOP: This modification was suggested following Kenwood Japan’s advice, that
“The I.F circuit diagram was correct and the I.F. board was labeled incorrectly.”

Kenwood Japan have now changed their mind and confirmed
“The I.F circuit diagram is incorrect.

Swapping R149 and R150 probably increases sensitivity to similar degree as achieved by just turning the AGC off

Please review KI4NR’s email below advising the (Kenwood intended) correct construction was electrical layout of the AGC identical to the TS-930.
KI4NR advises the rising S meter caused is leaking in C128 and C130.
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