Hello Folks. I'm trying to fix my solid state guitar amp/PA. The issue is that sound fades in and out after it warms up a bit and not at regular intervals. The power light by the power switch is on when this occurs. I have dug around in there and there seemed to be an issue with the reverb wiring and I re-soldered what I thought was the problem ( because it seemed to work ok after that ) However the problem still exists. The amp/pa has two channels, channel 1 has an xlr jack and a 1/4" (I tried only plugging the mic into channel one and the guitar into channel 2, didn't seem to matter) and two 1/4" jacks, one active and one passive on channel 2. It also has a low filter switch that either is set on cut or boost, and this seems to be on the 2nd channel. Sometimes when I change the switch setting on the filter it seems to bring the sound back. coincidence? Any help would be appreciated. Also, I am a licensed electrician so I have some electrical theory floating around in the ol' brain. Thanks