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TS940 Fan just stopped............ ahhhhhh

Active Member

TS940 working, yep still working.  940 was sitting on 20M listening as I was in the room all day doing emails and stuff.

I use this unit almost everyday. Monitoring nets and DX as well. 

Was sitting on recv for about 5 hrs yesterday, and the fan will sometimes cycle up, but its a working, receiving, transmitting unit. 

Since the room was quiet, I noticed that the fan had just stopped spinning, slight smell of something? Plastic, wax?  

Symptoms: REAR LEFT heat sink cooking hot. (PWR section) 


Remove FAN, apply 12v fan spins fine. Reinstall fan. 

Thermistor TH101?  Reading 18V on one side of the thermistor, and 9+ and rising with temperature slowly as it should, when the rear heat sink gets pretty hot, its 12.4V... Fan should have turned on by now.....

This is in RECV only, no XMIt...    I dont want to heat this up anymore than it should by XMIT, but it tested today at 100W. 

SO, no fan spinny... 

Noticed mains DC voltage is at 44VDC... A little high, but 29.05VDC is being fed to the AVR unit thru Fuse F1. Good. 

R17... hmm. 10K ohms. Normal 18VDC on one side, zero vdc on the other.  S/B 21v ? Maybe? 

So, heatsink is heating up, just sitting in RECV.

Those nice TAB mounted things Q103/Q104/ IC101(regulator 7805) ?  Mounted on the back of that heatsink are cooking........   

Is this a candidate for a New Replacement AVR board? 

Maybe I caught  it in time not to do damage. 

It's now very sad and covered up in the dark in the basement on the bench. 


If you think just getting that AVR board will make this happy, I'll order one today. If you think I need additional parts like the Q103, etc. please recommend it.  



NEW CALLSIGN is W2ADX --- (attn Moderators) 






Topic starter Posted : 15/12/2018 8:19 pm
Active Member

Well, I've watched the videos, and I think I'm convinced. REMOVE all that stuff and replace with PS and AVR board. Makes alot of sense. 


might be the thing that saves this radio. 


Topic starter Posted : 15/12/2018 9:08 pm
Active Member

the convoluted way they control the fans is bound to fail. Id just hook them up to the 9 volt rail and have them run all the time. 

the new board makes this easy.


George NE2I 

Posted : 17/12/2018 12:35 pm
Member Admin

That is really why I decided to redesign the entire thing. The way Kenwood originally designed the power supply leaves a lot of things to fail. But I can't really fault them at all. That was the available technology back then. The fan control is really one of the biggest problems and the fans quite often do not come on at all. With the new supply and board, the failure rate seems to be really low. I agree that replacing the supply is the best solution. And trying to repair the original AVR board is also a great challenge. 

But I am a little closer to the situation than some. Anybody else have any comments on this one?

Posted : 17/12/2018 2:50 pm
Active Member

ordering the kit...... I can't bear to see it sleeping in the dark... thanks. 


Topic starter Posted : 17/12/2018 6:41 pm
Active Member

We're unable to process your payment at this time. Please try again later.--------------  uh o,,,,  

I can't process via paypal, something went wrong. 

Will contact you via phone?  I'm available from 4pm-8pm EST...   


Topic starter Posted : 17/12/2018 6:46 pm
Active Member

all better now - order placed....  done. 

Topic starter Posted : 17/12/2018 6:57 pm