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Marshall valvestate 8100 blowing fuses

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  • Marshall valvestate 8100 blowing fuses

    I have this marshall valvestate model 8100 that's blowing fuses. I've checked the output transistors, diodes, and caps. All those components checked ok. Something leads me to believe that there's a component shorted in the circuit somewhere. I'm starting to wonder about the hard-mounted ic's. Any ideas?

  • #2
    What ICs, the op amps? They are not going to blow fuses. But to be sure, measre resistance from +15 to -15v. If they are shorted together, look for a bad chip.

    I am surprised there is not a shorted output device, that is usually what goes wromg with these.

    SO start from the start. Pull the secondary wires off the board. Does the power transformer - now unloaded - still blow fuses? If so, then disconnect the HV autotransformer (tube supply). ANy help?

    If the transformers work OK alone, then the trouble is on the board. If you have checked everything, then the board must have come out, so there is no piece of hardware stuck under the board or somthining, yes?

    Recheck each side of the rectifier bridge for shorts . Verify both power rails are not shorted to ground or to the speaker out trace. MAke sure the tube HV supply doesn't have a shprted rectifier or filter.
    Education is what you're left with after you have forgotten what you have learned.

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