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Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => The Newcomer's Forum => Topic started by: Tk6831 on May 07, 2020, 10:51:39 AM

Title: CRATE GFX-20 doesn't work, just makes humming noise when powered up
Post by: Tk6831 on May 07, 2020, 10:51:39 AM
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?
Title: Re: CRATE GFX-20 doesn't work, just makes humming noise when powered up
Post by: tonyharker on May 07, 2020, 11:04:59 AM
Is the hum affected by the volume/gain controls or is it there all the time. And is it LOUD.
Title: Re: CRATE GFX-20 doesn't work, just makes humming noise when powered up
Post by: Tk6831 on May 07, 2020, 11:13:36 AM
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.
Title: Re: CRATE GFX-20 doesn't work, just makes humming noise when powered up
Post by: Enzo on May 07, 2020, 12:44:59 PM
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.
Title: Re: CRATE GFX-20 doesn't work, just makes humming noise when powered up
Post by: Tk6831 on May 07, 2020, 01:56:15 PM
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.
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