crate glx1200h buzzes all the time

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i have a crate glx1200h half stack. whenever i turn the amp on it buzzes loudly. i have tried turning down all knobs, unplugging all plugins, and hooked the head up to a different cabinet. no matter what whenever i turn on the amp it buzzes loudly all the time. has anyone ever had this problem? can anyone give me some tips on how to troubleshoot this problem?
 
Yes.

First, this really ought to be in the instrument amp section, so if you can't find this thread, they may have moved it there.

Look at your speaker cones, when you turn the power on, does the cone move one direction and stay there? If so turn it off immediately and do not turn it on with a speaker connected until it is fixed. That would mean ther was DC on the speaker leads. Disconnect the speaker and verify with a meter if there is DC on the speaker wires. DC will damage your speakers.

That is one reason for loud hum. The other is a loss of filtration. Wiggle your main filter caps and see if the hum intermits. If so, they need to be resoldered. Otherwise you may have a bad one. Bad filter cap will not put DC on the output.


Other things are possible, such as a problem on one of the 15v supplies or a missing one.
 
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