Zenith 20XT20 Chassis Problem

[CoogarXR]

Hey guys-

I don't know if you guys ever get into solid-state zeniths, but here goes.

I have a X930 console with the 20XT20 chassis. It sounds OK at low volume, but only with the bass knob at 75%. Any higher and the bass distorts. The higher the volume, the more you have to cut back the bass to fight distortion.

I have had this model before, and I know what it is capable of. The problem is on all inputs, and on both channels. I tried different speakers too. I pulled the chassis and cleaned all the pots and switches. That fixed some other issues, but it still sounds very flat and crappy.

Anything I should try? I could re-cap it, but I hate to just throw parts at it guessing. I wish I had an oscilloscope.