Roland KC-300 Works for a bit then goes into severe distortion

[Doc38343]

Roland KC-300 Works for a bit then goes into severe distortion.
When I put on the bench with my tone generator it was clear at first but when i raised the levels past "5" on input gain and main output it started small distortion at first then when i did a full sweep thru the frequency range it suddenly went to severely distorted.
didn't know if any of you guys had seen one do this, going to try and find the schematic to start testing.
Thanks

[redwire]

Re: Roland KC-300 Works for a bit then goes into severe distortion

I found this Roland KC-300 preamp schematic, haven't looked for the power amp schematic. This can help you see if the trouble is the power amp or pre-amp.
Keyboard amps are different from guitar amps, they have wider freq. response and not designed to overdrive.

I use a clean line-level audio source, like CD player and listen to each section. You can inject (CD player) into the power amp input for example.

These things get beat up, so fractured solder joints, broken pots, trashed speaker, damaged op-amp etc. are the things I look for.