SX-680 no audio out

Renov8r1

New Member
I picked up a SX-680 off of craigslist cheap. It lights up, tunes ok, but no audio out. .85v dc at the speaker terminals. All fuses look ok. What should I check next? Appreciate any advice!
 
It does appear to have STK "chip amps".. First thing I would verify you have proper power supply voltages going to the chips.
 
Pins 2 and 9 on each of the chips are the + and - rail voltage. These must be pretty close to equal. Looks like + and - 30vdc.
 
Do you have around 45vdc at the emitter of Q402 in the power supply ?
 
Suspect...R401 33Ω and/or C404 220µf/ 63vdc. check them both.
 
My Harbor Freight dmm does not seem to be up to the task of measuring anything other than voltage. I need to find a better meter...
 
Just measure the voltage on both ends of R401. I already know one end will be 1.4 volts. The other end of R401 should be about 51 volts. If so the resistor, R401 is bad.
 
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