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Marshall G80R CD lights up no output

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  • Marshall G80R CD lights up no output

    I am by no stretch an electrician s forgive my inept description. If its straight forward I can probably fix it but obviously need some help to identify the problem.

    This amp lights up but there is no output. I have tried a different speaker and input a signal from the guitar jack and the cd.

    The circuit looks good with no obvious dry joints. There is one component which has a slight burn on it looks like a wire burn across it but otherwise it looks fine (and no sign of any other burning anywhere nearby). It is a fairly large white chalky looking tower, I think two legs. It is marked as M7 I1C 270RJ.

    There are several of these tower like components the others are marked variously M7 H1C 330RJ and M7H1C R33J.

    The burn on this component doesn't look like a showstopper but then I don't know what it is so Identification would be a start.

  • #2
    270R = 270 ohms
    330R = 330 ohms
    R33 = 0.33 ohm resistor

    Start by trying headphones if it has a phones jack.

    If that is dead too, then start looking for operating voltages inside and any blown fuses inside.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Thanks enzo. I'll see what I can find. Any idea where I can get a circuit diagram for this amp?

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      • #4
        Oh, look around, you'll find one...
        Attached Files
        Education is what you're left with after you have forgotten what you have learned.

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        • #5
          Marshall G80R CD

          Originally posted by Enzo View Post
          270R = 270 ohms
          330R = 330 ohms
          R33 = 0.33 ohm resistor

          Start by trying headphones if it has a phones jack.

          If that is dead too, then start looking for operating voltages inside and any blown fuses inside.
          Finally got around to trying again with this amp and checked for fuses dry joints etc. I was going to put the circuit into a modeler so I could lazily check all the values against a potentially working amp circuit. But didn't get too far with that idea.
          So I've returned to the amp itself. I now have output from one channel (clean) but not the other. The R111 component on the circuit diagram is getting very hot and I would think that the R112 is getting hotter than perhaps it should. At the moment that is all I can find that is perhaps obviously wrong (apart from the output )
          I'm still working on what values I should be reading for each component so can't provide any other clues just now.
          Would replacing these resistors be the solution or are these just symptoms of something else that is wrong?
          Also are these readily available or can an equivalent be used as a replacement.

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          • #6
            Those resistors are normally not, they serve the 15v zeners for the low voltage power supplies. Look for them on page 5 of the drawing. FInd those zeners. is ther 15v across each? If so , the resistors are doing their jobs.
            Education is what you're left with after you have forgotten what you have learned.

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