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TK-760 no TX audio

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westcoaster

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Aug 4, 2005
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141
Not as clever as I thought I was...

Got the lights working in the back panel on the TK-760 but in the process messed up my audio on transmit. I key up the mic, receiving radio receives a signal, I scream into the microphone but nothing comes out on the receiving radio...

By swapping various parts around using other TK-760 radios I have here, I have determined the problem to be in the head. (makes sense as that is what I was working on to restore the lights...)

First question. What is this mystery mini board? With the micro components it isn't something someone would cook up on their work bench.



red wire comes of IC 407 (voltage regulator)
Black wire goes to ground
Yelow wire to D 404 DC switch part of active filter amplifier
blue wire to C 488
Trace is cut on board between D404 and C488

Wondering if ripping this thing out would restore my audio on transmit



bit of background...
Bought this kenwood TK-760H radio for $80 on the weekend. LED's were flickering in the back of the display. Tap the radio lights start working etc. touch the LED's with a soldering iron and locate the cold solder joinnts. I also touched Q 405 abd C471...
 
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WX9EMS

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Jun 23, 2010
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Location
Lake Geneva, WI
The IC appears to be an Op-Amp according to my quick search, to what function I am unsure. When I get home and am sitting in front of my PC, I might be able to help you out further. If a trace was cut, then this is an added part. Are there any numbers or names on the board? What is on the other side? where does it mount? I believe I have a service manual for this radio, but it might not cover this board.
 

WX9EMS

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Jun 23, 2010
Messages
155
Location
Lake Geneva, WI
First things first, is this an 760 or 760G? I can't seem to locate a schematic of the control board. I don't really feel like taking my 860 apart to see what is or isn't there (assuming that part of the boards are similar). I would say that this is an amplifier of sorts, what sorts you ask, your guess is as good as mine. You could try to remove the board and repair the cut in the trace. You had mentioned robbing from other 760's, did you try to swap to a different control board? If it were in front of me, I could figure it out. Anyone else have any ideas?
 

westcoaster

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Aug 4, 2005
Messages
141
Thanks for the reply,
Turns out I was particularly ham fisted when handling this board. I found a 10K variable resistor at VR401 that was broken. Replaced the resistor and the radio now works.

Still a bit of a puzzle what the baby board does though.
I have two other TK-760H (not G models) and neither of them have this little board in them. I also have a service manual but this little board is not mentioned.
 
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