SX-680 no audio out

[Renov8r1]

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!

 

[avionic]

.85v dc at the speaker terminals.

Are you hearing and relay click shortly after power on ?

 

[avionic]

850mv is extremely high DC offset.

 

[Renov8r1]

No click. Does this unit have a relay?

 

[avionic]

No click. Does this unit have a relay?

Sure. Make me look up the schematic. No it doesn't. So... nevermind..
850mv is still way way to high.

 

[avionic]

It does appear to have STK "chip amps".. First thing I would verify you have proper power supply voltages going to the chips.

 

[avionic]

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.

 

[Renov8r1]

The voltages look good. + and - 34.5vdc.

 

[Renov8r1]

Update +33.9, -34.3; +33.9, -34.3

 

[avionic]

Do you have around 45vdc at the emitter of Q402 in the power supply ?

 

[avionic]

+33.9, -34.3

Well theres about - 400mv of DC offset right there.

 

[Renov8r1]

No, it appears to be 2.1vdc.

 

[avionic]

No, it appears to be 2.1vdc.

The collector of Q402 should have around 50.4 volts. Is that voltage present ?

 

[Renov8r1]

No, the collector voltage is 1.4v.

 

[avionic]

Suspect...R401 33Ω and/or C404 220µf/ 63vdc. check them both.

 

[avionic]

I have to get some shut eye. Got to work tomorrow early.

 

[Renov8r1]

Thanks for all your help! I will post the results. Good night!

 

[Renov8r1]

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...

 

[1MEGΩ]

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.

 

[Renov8r1]

Ok. I will do this tonight.