gibson g20 troubleshooting help

[livebaitdrifter]

need a little help here.
i have a gibson g20 that powers up has 28v output from transformer but makes just a low hiss from speaker. inspection of the board shows no burnt or blow resistors.
any ideas of what to check would be helpful. im a electronic technician but have never fixed an amp
thanks
the drifter

[52 Bill]

Welcome to the place.

Try and get a schematic for the amp at the Gibson site.

You need to find out where the signal stops by isolating the amp circuits. If these is a hiss coming from the speaker, the power amp is probably working. If you can figure out where the power amp input is, try touching your meter probe there and see if you get a hum from the speaker. If you do, then keep moving to the front end of the amp to see where the signal stops. I could be as simple as a bad input jack.

If you change the volume and tone controls, does the sound of the hiss from the speaker change?

[livebaitdrifter]

thanks for the reply

The schematic is on the back panel of the machine but the board has no printing on it so i dont know what each component is part of. Ill try to get a gigson manual somehow.
Looked like a few weak solder joints at the rectifiers, i fixed those but no diff, some corrosion on a big resistor and sometacky stuff on the board that looks to me like rosin.

kenny