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Marshall Valvestate 8080 hum and crackling problem
Hi, I have this old Marshall guitar amp that hasn't been used for a long time.
When turned on it produces uncomfortable humming noise that is not a problem when practicing with a band but it makes that amp unusable for studio recording. Also there is a crackling noise when I crank up the volume both on clean and boost channel. And when I turn it off there is a little boom when the switch flips.
I cleaned all the potentiometers with a cleaning spray, fixed something in the sound but the main problem with the hum remained unchanged. It is not affected by anything, it is there even with all controls to 0 and no input jack connected it just stays fixed. The crackling is more quiet when I plug the input jack directly to return input.
What I suspect the culprit might be: Two big 50V 2200uf capacitors on the board seemed a bit loose, so I tried to wiggle them a bit when plugged in and one of them produced a big spark, there is some glue residue (it doesn't look like electrolyte leak to me but I'm not really skilled in electronics repair) and when I wiggled with that capacitor when the amp was turned off, also out of the socket, it turned that amp on for a brief moment.
I don't know much about electronics, I can do some simple tasks like changing certain components but not some complex diagnostics. Has anyone dealt wíth something similiar? Could those capacitors be the problem?
Schematic: https://www.thetubestore.com/lib/the...-Schematic.pdf
When turned on it produces uncomfortable humming noise that is not a problem when practicing with a band but it makes that amp unusable for studio recording. Also there is a crackling noise when I crank up the volume both on clean and boost channel. And when I turn it off there is a little boom when the switch flips.
I cleaned all the potentiometers with a cleaning spray, fixed something in the sound but the main problem with the hum remained unchanged. It is not affected by anything, it is there even with all controls to 0 and no input jack connected it just stays fixed. The crackling is more quiet when I plug the input jack directly to return input.
What I suspect the culprit might be: Two big 50V 2200uf capacitors on the board seemed a bit loose, so I tried to wiggle them a bit when plugged in and one of them produced a big spark, there is some glue residue (it doesn't look like electrolyte leak to me but I'm not really skilled in electronics repair) and when I wiggled with that capacitor when the amp was turned off, also out of the socket, it turned that amp on for a brief moment.
I don't know much about electronics, I can do some simple tasks like changing certain components but not some complex diagnostics. Has anyone dealt wíth something similiar? Could those capacitors be the problem?
Schematic: https://www.thetubestore.com/lib/the...-Schematic.pdf
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