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Author Topic: TS-940S won't power up.  (Read 2434 times)
N1SQJ
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Posts: 13




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« on: September 21, 2009, 02:40:23 AM »

My TS-940S always worked fine. While giving a whistle into the mic on SSB the rig shut off suddenly and will not power back on. I had it on a dummy load..flat swr...was trying to check peak wattage reading, so thats when it bit the dust.
I checked 2 fuses they are ok. I checked for 28V on both taps, they are ok..  (32v and 34v). That voltage comes on when switched on, but nothing lights up and no power relay or anything else is heard. I'm hoping someone has an idea of the problem spot. Thanks!
Rit  W1RWV
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K5BOX
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Posts: 5




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« Reply #1 on: September 21, 2009, 03:59:27 AM »

I had a similar problem and discovered the TIMER BUTTON was pushed in.Check your user manual
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N1SQJ
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Posts: 13




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« Reply #2 on: September 21, 2009, 11:30:41 AM »

I thought of that, but that wasn't it. It's as if on the peak output, it overloaded something and some sort of protection kicked in.
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K4CFQ
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Posts: 18




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« Reply #3 on: September 21, 2009, 07:00:10 PM »

Sounds just like the problem I had with my TS-940S.  I ended up putting it in a shop for repairs.  I forgot exactly what was the cause but a rather minor component failed and had to be replaced.  Now the ole TS-940S works AOK.  Note:  Be sure and check your fans... over heating can cause a serious problem.  The stock fans are known to give problems (slow or stop running) after a few years use. There is a mod to get the fans to turn on sooner, and many of us mod the TS-940S fan housing to incorporate computer case fans ... they work much better.  I use a Silenx 80x80x15 12v fan.
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N2MG
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« Reply #4 on: September 25, 2009, 06:57:00 AM »

Clif,

Thanks for jumping in here.  We appreciate your help!

Mike N2MG
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N1SQJ
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Posts: 13




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« Reply #5 on: September 21, 2009, 07:14:56 PM »

I just did a resistance check on D1266 a silicon power transistor on the PS heatsink and it's open.. thinking I may replace all 5 transistors on that panel, since i hear that they just GO when they feel like it. I think I remember NOT hearing the fan on at time of failure, and it was getting warm, so hopefully I'm on the right trail. cant afford a shop right now, so going to try replacing these parts for now.
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N1SQJ
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« Reply #6 on: September 21, 2009, 07:56:17 PM »

.... just switched the leads the other way and got a reading so its not open after all. hmm.. dunno.
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K4DPK
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« Reply #7 on: September 21, 2009, 08:33:47 PM »

What about the 13.8 volt supply?

Phil C. Sr.
k4dpk
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K8GU
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« Reply #8 on: September 22, 2009, 03:04:55 AM »

When you say you checked for "28 volts on both taps" are you talking about transformer taps or the power supply outputs?  The power supply should be putting out a stable 28.5 volts, not 32+.  One thing I would try is  disconnecting the heavy power cable that goes to the PA.   See if your rig comes on then.
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KL0S
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Posts: 132




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« Reply #9 on: September 22, 2009, 05:50:55 AM »

Be really careful when you're probing around the AVR power supply board.  I was hot on the trail of what was causing my 940 not to transmit and I was on the way to the PA board when I was checking the AVR board and inadvertently shorted the supply when measuring the voltage there....then the radio didn't work at all!

Ended up sending it off to Clif at AVVid (check his feedback here on eHam).  Clif is the man when it comes to fixing Kenwood rigs and especially keeping our old faithful 940 friends working.  His rates are VERY reasonable with a quick turn around....highly recommended.

Dino KL0S
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KA5IPF
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« Reply #10 on: September 22, 2009, 10:45:56 AM »

Measure the voltage on the fuse on the AVR unit. It should be 28.5v DC. If not fix that first.

The 2SD1266 is the regulator for the 21v supply which is located in the front left corner of the AVR unit. If it opens up (very common) then the 21v supply dies and the radio will not turn on. When you replace the transistor solder the leads to it. The plug gets overheated due to weakened spring tension and loses contact and is the cause of most of the failures.

Clif
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K7KBN
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Posts: 2753




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« Reply #11 on: September 22, 2009, 10:54:41 PM »

May have overstressed something by whistling instead of speaking in a normal tone of voice.  There's a local language used in the Canary Islands that actually involves whistling.  Unless you're from there, I'd recommend against whistling into a microphone connected to an amateur transmitter.  The circuitry will thank you.
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73
Pat K7KBN
CWO4 USNR Ret.
N1SQJ
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Posts: 13




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« Reply #12 on: September 23, 2009, 01:12:43 PM »

Thanks OM, I should have known better about whistling. Progress: I did try to get a voltage reading from the white wire to the AVR labled 28A and got nothing. I went from ground to there and then between there and the black and red wires, and still no reading. I since have just disassembled the heatsink and am ordering 2 - 2N5886 and all three of the TO-220 transistors because they are cheap and easy, so with everything apart I can't try unplugging the red and black wires to PA, but I guess after re-installation of parts,, I should try that first? IF-- I do, and that is the cause, then what am I looking at?,, a shorted final, or...? and if that is the case, then won't I re-fry my newly installed stuff all over again instantly? Getting ahead of myself, but I want to be methodical and not cause destruction. For now I took ohm readings of the red/blk wires to PA, in case this may tell a story. results: Short! I'm hoping in off position maybe thats a closed relay...? other readings: Just LUGS: 28A-FG=2K 28A-FB=short FB-FG=2K  Thanks Elmers, keep it coming, I miss my 940!
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N1SQJ
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« Reply #13 on: September 23, 2009, 03:25:09 PM »

I would like to learn some canary Smiley
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KA5IPF
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« Reply #14 on: September 24, 2009, 07:49:21 AM »

If the final power leads show a short then the zener protection diodes in the final have worked to protect the finals and drivers. Check D1 and D7, usually D1 but check both.

That tells that the pass transistors probably shorted and tried to put 45v to the final unit. It also means you need to look at if not replace Q1, Q2, D3, R1, R2, and R4. Also check the fuse and Q6 and D14.

Also look at the filter caps on the AVR unit, if the ends are swollen replace them

Clif
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