Marshall MG250DFX insane buzz without volume

[drummer turned guitarist]

alright, i have a marshall mg250dfx solid state amp. in the middle of a rehearsal the other day, it started buzzing very loudly. i checked my guitar, tried a different one, tried different cables, unplugged all the cables, and turned everything to 0, and it was still doing this. i checked the fuse, and its still good. i don't know what the problem is. I'm very open to any suggestions on what to do. Thanks!

[DrGonz78]

Describe the buzz a little more in detail. Is it more like a hiss 120hz or a lower buzz like you get from touching your finger to the tip of a guitar cable when the amp is on? The fact that you have turned down all the volume and the noise still persists tells us that something component wise is either bad or the connection to it is finally not working well. You still get sound from the guitar or is it just the "buzz" with no guitar signal?

[Enzo]

More importantly, look at the speaker cone, when you power on, does the cone move one direction and STAY THERE? If so, that is DC on the speaker - TURN IT OFF IMMEDIATELY.

Disconnect the wires from the speaker and put your meter leads to the wires. Verify if there is DC voltage there when power is on.

If that is the case, you have a blown power amp module.