Ampeg SVT4-Pro clipping, why?

[drewl]

So the preamp "peak" light on this amp comes on way too early causing a nasty distorted sound since the preamp is clipping too early.

Power amp is working as it should, full power out

Went through the troubleshooting steps on the schematics, and everything is fine up to U2.

Pre Signal at TP6 is good, after R102 (68K) the signal is attenuated a lot, you can barely see it at U2 pin 2, and U2 pin 1 is clipped severely.

Replaced U2, still the same.
Replaced J112, still the same.

I put a cap across R102 and peak light goes out, and signal at U2 pin 1 is just beautiful and amp works perfectly.

Any idea why this is happening and why a cap across R102 fixes the problem?

All the test voltages are as they should be, tubes are fine, I thought maybe C25 was leaky, but it is fine.

I thought maybe the EQ FS signal might be the cause, but it is switching fine, I thought for sure J112 had to be bad, but I socketed it and tried a few different fets.

Weird.

[Jon Snell]

I would check TP6 for the presence of a DC offset voltage that may upset the FET.

[drewl]

That's what I thought, but no, zero volts dc there.

One theory I have is the traces on this board seem really thin and maybe it's being loaded down.

It all checks good with a meter, but you never know.

[Dave H]

Pre Signal at TP6 is good, after R102 (68K) the signal is attenuated a lot, you can barely see it at U2 pin 2,

That's normal Pin 3 is grounded making pin 2 a virtual ground.