Need help trouble shooting peavey Mark III amp

[vjw757]

I have an old peavey Mark III amp. I do believe its a bass amp but i use it for guitar. Great amp.

Problem 1:
When i turn the amp on and off i hear a pop. Its gotten to the point that im afraid that it will damage my speakers. I have a $950 Marshall cab. So now i just unplug the cab when turning it on and off.

Problem 2:
when playing, now i hear static. Makes me think one of the pots went bad. At least thats what im hoping.

Here are some photo of the circuit board

Pictures by Vic_Williams - Photobucket

[Jazz P Bass]

Is the turning off pop something new?
It sounds like the amp needs some basic servicing.
It is an old piece of equipment.
Thermal cycling, bumps, bangs, smoke, dirt.....
Resolder all of the major components & headers, clean the pots & jacks.

[olddawg]

You have a dc spike. That can be caused by a number of things. If the spike suppressor caps on the power switch are bad it can cause this. So can an ascing old power switch. But it can also be caused bu failing coupling caps and other stuff. You need to find out if there is DC present on the output when the amp is running. You also need to know if it has a muting circuit. Some amps mute the output when you switch them on to avoid this. Without a schematic it is hard to tell. If it has a main amp in jack, plug a cable in it and switch the amp on. If there is no pop the amp is passing dc from the preamp section. If it has a pop it is in the output section.

[jrfrond]

Those are generally reliable amps with a proven design, but they can develop cold solder joints, dirty connectors, etc. over the years.

I'm actually more concerned that you are unplugging the cabinet before shutdown, because you can cause a momentary short across the 1/4" plug, that is, if you are unplugging it at the cabinet end.