Crate GTX212 Squeals on power up

[booj]

About a 1k rail to rail square wave on power up. Power supplys look good. (+/- 37 volts with nominal or at least the same ripple on both rails). No noise in the preamp section and their +/- 15 volt supply is good. Oscillation is only present at the power amp stage. Looks like it has been serviced before and the outputs were replaced with ST TIP142's and 147's
I don't have a schematic. That's the next step.
Anybody had a similar problem or have a scat?
Thanx!

[Jazz P Bass]

Crate GTX212

I had a GK RB800 that did the same thing.
Never did figure it out
Built a 3 second delay/on relay circuit for the speaker.

[booj]

Boy, I wish that would work! This never stops though. It's as if the input is connected to the output. Just hjave to wait for a scat.

[Jazz P Bass]

Crate GTX 212

Did you try inserting a stereo plug into the FX insert?
This should kill the preamp signal.
If it still oscillates, it is in the power output section.
I have attached the GLX series amp.
The output section may be the same as the GTX (or close)
Hope this helps.

[booj]

found it

The heatsink of Q19 which is connecxted to the differential pair was shorting to R57 which is a resistor in the input circuit. Loud technology sent a scat within 2 days of my request.