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Crate GX130C Pop then hum

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  • Crate GX130C Pop then hum

    Just got a Crate GX130C. Previous owner says he hadn't played it in years and the last time he did it didn't work. He plugs in his guitar and it works miraculously. I take it home, fiddle around with it for like 10 mins or so, then I hear a loud pop then a hum; no guitar sound at all. The volume knob doesn't increase the volume of the hum. This event can be replicated any time I turn the amp on. I wait a few hours, turn it on and play it for a few minutes and it pops and cuts out, but the lights and power stay on. I do not have another cab to test it with. Seems like an issue with overheating? I cleaned the internals of all dust and debris and all the solder joints looked fine. The only thing that looks off is the output transformer is either rusty or has some red dirt caked on it. Any tips would be greatly appreciated.

  • #2
    Schematic?
    - Own Opinions Only -

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    • #3
      If it were overheating, you could feel the chassis getting hot. Also, the speaker is working, you hear the hum.

      When it cuts out, ball up your fist and whack the top of the amp. Does that wake it up? Does the amp react in any way?

      Attached Files
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        What output transformer?
        - Own Opinions Only -

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        • #5
          Originally posted by Helmholtz View Post
          Schematic?
          Click image for larger version

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          • #6
            Originally posted by Enzo View Post
            If it were overheating, you could feel the chassis getting hot. Also, the speaker is working, you hear the hum.

            When it cuts out, ball up your fist and whack the top of the amp. Does that wake it up? Does the amp react in any way?
            tried this a number of times to no success, whacked the top and sides just to see if anything happened. Still only has a hum

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            • #7
              Can you see the speaker? If it is pushed forward or back (and stays there) when the hum happens, turn off the amp immediately. That will be caused by DC on the output which will burn the speaker out pretty quick.
              Originally posted by Enzo
              I have a sign in my shop that says, "Never think up reasons not to check something."


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              • #8
                ^^^^^^ Yes, that. I'd first determine if the output is DC or AC.
                "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                • #9
                  Well if this changes anything I plugged the amp into a different cab and had no issues, at least none within an hour straight of playing. Zero issues at all compared to the cab it came with. Still looking at a DC issue or could it be a cab specific issue?

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                  • #10
                    "output transformer is either rusty or has some red dirt caked on it."
                    This is what I found with my Crate ...generally a lot of oxidation on the enclosure. Any place where there are heat sinks bolted to the enclosure or ground connections bolted to the enclosure it is worth cleaning those bright/wire brush/light sanding and seeing if that helps.

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                    • #11
                      Yup it’s all about that output transformer.
                      When the going gets weird... The weird turn pro!

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                      • #12
                        Click image for larger version

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                        You mean the one that doesn't exist in this solid state amp?
                        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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