Differential stage

[brandes.cm]

Working on a Fender guitar amp, the output stages are essentially the same RF amps. I show two red circles on the schematic(collector of Q8, and Q11), I assume the signal at those two points would be the 1Khz input signal pulsing the rail voltage. I see no sign of the 1Khz signal. The transistors seem to read ok. Is there an easy way to use DC rather than AC signal to trouble shoot this circuit?

thanks,
cory

 

[Perry Babin]

There's generally very little signal at those points unless the amp is driven to hard clipping. In what way is the amp malfunctioning?

 

[brandes.cm]

I have no output from it. It functioned at one point though. The output fets measure fine, no DC on it. I lifted the D20 and D10 thinking those are protection circuits, no help. Maybe I need to focus on the lower left hand side, muting pin.