Loud Midrange Squeal

I have become the owner of a Soundtech PC-1250 Powered Mixing Board, and I am interested in making something more than a boat anchor of it. When I obtained the unit I was told the building it was in had suffered a lightning strike, and it hadn't worked since. I took it home to find out what I could and I am stumped as to how to proceed. When it powers up, it emits a constant midrange squeal that is very loud out of all four outputs: R, L, Mon. A, Mon. B.

If it were silent I know a thing or two to try. I don't own a scope. Can someone please help me to isolate the origin of this signal so I can proceed?

 

Do you have a schematic of the board?

The failure is something common to all channels, such as the power supply.

 

I am working on obtaining the schematic. Soundtech evidently has a strange relationship with the public and professional community. Does anyone on this forum have the schematic?

 

When I was being trained centuries ago..... the cardinal rule is:
Always assume the power supply is the problem until proven otherwise.

A lightning strike could over stress and damage just about any component. What happens is the parts that "break down" first act as zener clamps to save the other parts. Post a schematic and we can all guess as to who died first.

 

View attachment PC830,Pc1250 - Schematic[1].pdf That was easy! Just a phone call, and I spoke with an organic interface almost immediately!

 

Found the schematic. some of it is difficult to read. Checking what I know how to check.

 

Showed this unit to a friend. He agrees it's probably a pwr supply issue, but gave me reason to skeptical of a lightning strike being the cause.