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May 29, 2020, 08:54:55 AM

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Author Topic: CRATE GFX-20 doesn't work, just makes humming noise when powered up  (Read 1468 times)

Tk6831

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I have a CRATE GFX-20 that doesn't work, just makes humming noise when powered up. I have looked over the circuit boards and don't see any signs of bad components or bad connections.

Circuit board # 07-256-04

Any ideas where to start?

tonyharker

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Is the hum affected by the volume/gain controls or is it there all the time. And is it LOUD.

Tk6831

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not affected at all by any of the controls. It isn't objectively loud. Not really a low electrical hum, probably a volume level of 4-5 I would say.

Enzo

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Watch the speaker cone closely.  When you turn the amp on, does the cone move one direction (in or out)and stay there?  IF so,, TURN IT OFF.  You will damage the speaker by leaving it on.  That means you have DC on the output, which means a bad amplifier chip.

Other possibilities are failed or disconnected main filter caps.

Tk6831

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I did use a 9v battery to make sure the speaker was good and it is wirking fine. I will try your test when I get home.