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Dead solid amps & when they are worth/not worth fixing
MUFF WIGGLER Forum Index -> Guitars, Basses, Amps & FX  
Author Dead solid amps & when they are worth/not worth fixing
controlFreak
Recently acquired a Marshall Valvestate 8100 from the early 90's not powering up and blowing fuses. Dead Banana It didn't cost me anything. It was easy to fix.

It was easy to take apart.
This is a big factor for me when looking at amps for potential refurb or using as chassis donor for a home build. If it is going to be a pain to take apart/put together, it may eat up too much time to be "worth it." I also hate seeing stuff going into the trash/landfills/oceans, so I'm pretty lenient, personally. I will generally make an attempt to open it up just to find out what I'm dealing with.

In the case of the 8100, the problem was easy to spot. Two discolored 33ohm metal oxide power resistors (rated to 5w). Upon checking the schematic, these are a crucial part of the output circuit- basically keeping the power transistors in check. Upon probing with multi meter the resistors' value had drifted to ~20ohms and the power transistors were reading as shorted. Ordered new parts, a couple of 33ohm 7w resistors, and new equivalent power transistors, totaling a less than 10 USD. Amp worked, some pots were scratchy, changed those with parts I had on hand. I have another amp now and it cost me about 10$ and its actually pretty decent.

Rockin' Banana!

Welcome, feel free to share all your amp troubleshooting triumphs and terrors!
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