Fender FM 212r effect squealing

[Filip_Mikuz]

Hi!

I hope im not committing an atrocity mentioning an amp here, but the fact of the matter is that my FM 212r started going crazy and i think its the built in drive thats to blame.
The amp has a dirty sound on the clean channel thats not affected by guitar volume or master volume.
The amp stars squealing if turn on the drive channel, especially if i bring the guitar to close. This squealing is affected by the drive pot.
http://support.fender.com/schematics/guitar_amplifiers/FM212R_schematic.pdf
ive checked the amp board and components look fine and so does the leaded side.

thanks for your help!