The preamp section has about 4 Jfets in the area of the far right side that if any one of them are to flake out it will mute the head. It's not something that you can inspect visually. I had an EVO III with the same problem and wound up replacing 3 of them until I hit on the right one. They only cost about .10 but you have to clip the center lead, effectively destroying it, to troubleshoot.I have a recent ABM 600 evo 4 that has gone silent . Does anyone care to recommend a repair/tech in Birmingham, Atlanta, or Nashville ? Are there fuses I could check ? -thanks in advance-Oatis -The lights come on but NO hiss or hum through the speakers.
A signal generator, AF monitor, and O'scope come in handy. If you're not a tech, best to take it to a qualified repair center.
The schematics vary on these from generation to generation, and even some series within the same generation.
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