Hey Everyone-

First post.  I've been checking out different posts by Lab Series users and have been working on mine for a couple month on and off and have not been able to solve the issues.  I'm still a novice at amp repair so I'm wondering if some of you old pros could at least point me in the right direction.

I have an ooooold l7 Lab series 4x10 combo which produces very ugly distorted sounds when a note is plucked hard.  Light plucking doesn't produce a sound at all. The first two channels work at maybe 10% volume and the second two work at reduced volume as well, but are noticeably louder.  I've checked the speakers and power amp in and at this point I'm thinking it is the power supply-  So far I've replaced a dead diode, but I've found several more with black soot on the leads and am wondering if this is a sign of failure?

Also, the sound is too screwed up to give a qualitative test the compressor but when turned on, the led will be lit for about one second then quickly fade.

Anyways, thanks for your help in advance and I apologize for my lack of knowledge  :duh