Fender M80 - square wave generator!

[Ron]

Hi all - this is my first here!

I'm trying to fix a Fender M80 (single 12) amp for a friend. It's making rail-to rail square waves at its output, regardless of control settings. Primary and 16v. supplies look reasonable, and there is no sign of trouble at any of the TLO72 amps that seem to handle front end function.

Without a schematic, I'm guessing that U6 - an MC1436 - is being used as the power section pre-driver, and it has squares at both its power pins and its output. Has anyone had this symptom? Or a schematic of the power section?

Many thanks!
Ron

[Enzo]

Are you saying that with no input and the controls all at zero, the amp produces full power squares?

Look at the power rails for the power amp. Anyone lost the filter cap? Likely just a resolder if so.

Send me an email with Fender M-80 schematic as the subject line and ask for it.

tmenzo at msn dot com