Slightly distorted Fender Stage 112 SE

[Randojazz]

I have a Fender Stage 112SE amp with slight distortion. I have read all the previous posts about this amp. Everything that was discussed back then I have remedied. However I did notice that when I connect an external speaker to the external speaker jack, the distortion goes away but R75 and R76 begin to cook. When I disconnect the speaker the distortion returns and the resistors cool down. Any ideas? Thanks, Randy.

[g1]

C49 connects those resistors to the output. Check that it is not shorted. Otherwise, the only thing that could make them cook is high frequency oscillation. If it is an oscillation problem, it is likely causing the distortion and getting even worse with the ext. speaker.

Here is the schematic, not a very good print though.

[Randojazz]

Thanks g-one for the reply. I do have the schematic, and I did check C49. It is not shorted. My meter has a cap checker and it does check .1 mfd. As for the high frequency osc. not sure how to go about checking that.

[Randojazz]

I wasn't suspecting oscillation, only because the output transistors are not heating up.

[52 Bill]

A lot of these amps will oscillate if lead dress isn't watched. In fact some of these amps will have speaker leads cable tied away from the board and hooked to the rear panel.

The extension speaker jack is connected to the power amp input chip. It changes the gain resistor or something which is probably why it only happens when you plug in an extra speaker.

Be sure to check the entire board for broken off feedback/snubber caps which is a fairly common problem.

[Randojazz]

Thanks 52 Bill. I'll go over the board, capacitors, and connections once again.