I have a weird fault in a JC-120 that I can’t diagnose precicely. I get heavy clipping distortion on the power amp when I’m only at 2-3 on the volume knob. I’ve traced the issue to the power amp and likely one or multiple of the Fets have gone bad, but I can’t seem to figure where the fault is exactly. Any tips what to look for? Running the specified voltages in the schematic the amp measures good and clean until the output, but it clearly distorts too soon.
I’m getting clipping after Q26 and Q27 on the Power amp. Taking out the Effects board and Line Out board lowers the distortion slightly.
PSU voltages measure as follows w/ no AC ripple:
+VA: +31V
+VB: +19V
+VC: +16V
+VE: +44V
-VE: -45V
The schematic doesn’t specify what +VA, or±VE should be… But +VB and +VC are correct, which leads me to believe that the PSU is fine.
Any help would be appreciated.
Edit: The 120UT_JT schematic available online matches the amp except for a couple components.