Kenwood Ts-940 S-meter Problems
I recently aquired a TS-940SAT as a backup rig. Everything functions, but there is something odd about the receiver. Either there is something amiss with the S meter or there is a bigger problem in the IF or RF stage.The symtom:The receiver goes from almost dead to very hot. During a QSO, a received signal can almost instantly go from an S1 s-meter reading to 40db over S9, and then drop back down.
S-Meter adjustments. I suggest you to revise the famous TS-940S receiving performance to be even better, of course! Our next step will be identifying different N-FET's for replacement. The 2SK125 is discontinued. Probably by using modern FETs, the receiving performance will increase.
There almost seems to be a 'threshold' point, that once over come, the sensitivity soares. I don't have much experience with the TS940, but the selectivity does not seem to be up to par. I don't know if these are related.I have a 756pro that I have been using in an A B comparison.Any thoughts would be appreciated. Anybody have a spare Service Manual for the 940?73,KeithKC1XULogged.
I had a situation a year or so ago in which signals would appear to fade out over time (say 2 or 3 minutes). One minute the signal was S-9, and then, a few minutes later, you could barely hear it.
The S-meter reading went to zero, as well.It turned out that the internal connection in the X VERTOR connector (used to connect a second antenna to the transceiver other than the one used for transmitting) had become slightly corroded and wasn't making good contact. I sprayed some contact cleaner into the connector and worked the proper DIN plug in and out a few times. That seemed to fix the problem.TedLogged. My 940 developed a similar problem last year. It turned out to be the relays which select resistors for the attenuator. These relays are located near the antenna connector on the RF board. Stepping through the attenuation steps you can see the two of them operate, almost in a binary fashion.
I removed the plastic cover and gave the contacts a shot of contact cleaner. The relays can be a little fragile so be careful if you attempt to drag a piece of paper across the contacts.
A little brass type spring pops off and the relay will stop operating if not replaced.The S meter adjustment has three adjustments: VR1 sets the IF gain for S1 at 1uv input. VR2 sets S9 with 50uv input and VR3 sets S0 with no signal input.Set VR3 for S0; VR1 for S1 at 1uv and VR3 for S9 at 50uv. The three adjustments all interact a little.VR1 is located on the IF board towards the front of the radio.
It is near the cutout section of the cabinet bottom grill.If all you have are bad relays in the attenuator you will probably not have to bother with the adjustments. After going through mine and repeating the steps 3 or 4 times the meter is pretty accurate. I was able to confirm my bad relays by removing the covers and tapping the contacts with a tooth pick. Also cycling through the attenuation steps would make it operate better for awhile.Good luck with the project.DickLogged.
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His equipment is up for tender at the local club. I'm a young ham (under 20) who's gotten a bit bored of the reliability of VHF, and I've been really wanting to get into HF.
A Kenwood TS-940SAT with auto-tuner installed caught my eye, but there's no ballpark price listed. The SK was a heavy smoker and owned the rig for about a year. It has no box or manual and 'appears to be in working condition'.As I said, I'm young and hence am on a budget.
What do you all think is a fair price for me to offer?. Easiest way to price anything out is to go onto eBay and search the 'completed listings' options. It will give you a base for what people are paying for both working and non-working options.
It makes you a much better and informed buyer. You can even print out/send the listings to the seller to prove the price s/he will be getting would be the best.This option is also great for figuring out what to sell items for. I have done this with a few estate sales. Cross-referencing the ebay prices and selling accordingly.Hope this helps!. I paid $410 for mine non-working and paid another $120 or so for parts. I would see a red flag though if the club can't test an HF rig and at least say that it put out 100W on all bands into a dummy load and can receive WWV and tune through at least one band without unlocking.The good news is that if you're handy with a soldering iron and desoldering braid, these can be fixed.
Very few surface mount components. The bad news is the 'dot problem' caused by PLL unlocks. If you can test the rig, tune slowly through an entire band and make sure it receives the whole way through and the display doesn't stop. Chasing a PLL unlock without being very careful and knowing how to troubleshoot electronics is a crapshoot I wouldn't wish on someone who's not up to the task.Minor problems involve the meter and sub-display lamps. The meter lamps are a pain to replace and often the lightpipe they connect to breaks the first or second time they get replaced.
I don't know that anyone has ever gotten one working again after breaking it, and it's a more expensive and hard-to-com-by part. Luckily, you don't strictly need it. The subdisplay lamps are easy to replace. I replaced mine with LEDs with no problem.These prices are US. I have no idea the relative values in NZ.Fully operational with no mic, I wouldn't say that $700 is out of line.Minor problems (fast clock, blown bulbs, etc) $550 or so.PLL unlock. I think $400 is fair if you can fix it. There's a divide in the production runs of the 940 where a heap of enhancements / fixes were done to correct some of the first generation issues.
If you can power it up then down again and the S-meter slams to the right, it's the first production run and may have some quirks awaiting discovery. Not a big deal though as the radio can still be just fine (and later models still had a few quirks lurking around.just different quirks). It might let you haggle it down a bit if it is a first gen. Most fixes are well documented online and are easy, if not a bit time consuming, if you're handy with a soldering iron.
Mines a first gen and I've seen other first gens asking around $450-$650 (CAD) at flea markets. A good second gen might still fetch up to $700-$800 with a few filters installed and a good desk mic.The 940 was one of the best radios of the mid-80's. If you want to know its age, take a look at the serial number.
The first digit is the year of manufacture, i.e. 5xxxxx was made in '85. Just keep in mind that was 30 years ago.
Kenwood Ts 940s Troubleshooting
If you're unable to test it and the condition is unknown, of course you'll be taking a gamble. Worst case is that it's DOA, and then you can either have a crack at trying to fix it or you can part it out. I probably wouldn't offer more than $400 if that's the case. That's why I won't be parting with mine and I'll probably buy another if I see a bargain. There seems to be a lot more popping up at fleamarkets over the last decade which I think is due to their age and, let's be honest, many (if not most) hams these days are button pushers and shy away from a soldering iron, not that there's anything wrong with that. I consider this radio to be one of the last solid and real (mostly analogue and non-'computerized') radios made.
Kenwood Ts 940s Manual
There are no surface mount components and everything is accessible inside and relatively easy to understand and work on.I forgot to mention earlier, the cooling system is perhaps the most important item of upkeep on the 940. Keep the fan bearings lubricated or replace the fans with some newer ones. It really doesn't like to get too warm. Don't know about other models. I believe the 940's were built from '84 to '92 so that should be 4xxxxx to 2xxxxxx. There were a couple of different places where they were built and they were given the serial numbers in blocks.
Kenwood Ts 940s Problems
I hear some folks saying that the 700000's and newer are the better radios, while others say the 800000's and newer. It's quite possible that some of the newer radios didn't receive the revised boards when some of the older ones did, due to the factory using up what ever serial numbers they had for that particular run. The meter slam is the easiest way to tell though.There are also some folks saying that the 700 range had SSB issues, but it's not all that noticeable. They were a fine radio and most of the complaints are just minor things that can be easily lived with. Can you check it out? I bought a 940 for $350. However, it was a bit of a deal to a newly licensed op from an Elmer who just finished building a K2.