HELP PLEASE!!! Rect-o-verb 50 combo buzzing

[Oky]

I have a M/boogie rectoverb 5o combo, about 2 years old, has been carefully looked after.

Only problem I have had was an (electrolytic) capacitor somehow broke off and was rolling round in the chassis. It was just out of warranty but the dealer had it fixed under warranty for me. Since then its been fine, until-

Lately I've noticed a buzz/hum and it seems to be getting louder.

I've tried 3 guitars, 4 cables with no change. With a short (6'') patch lead plugged in and nothing touching the other end the buzz is still there. It sounds kinda like an unsheilded single coil!

I swapped every tube out one by one and no change.

I tried turning off lights and appliances etc in the area, no noticable change.

Interestingly, when I touch the power toggle switches, or the channel toggle on the back, the noise quietens noticably just like when touching the strings on a bodgy guitar! Which implies an earth fault?

Anyone got any Ideas?
Could it be the house mains wiring?
Or is it (shudder) my amp?

Thanks in advance...

[ChrisK]

What frequency is the buzz?

If it's 50 Hz., it's another cap or the internal ground (as in that third safety ground thing). Mesa do not publish schematics for amps still in production.

Since touching it seems to have an effect, One might surmise that the chassis isn't touching the right places.

I have one of these. It buzzes, but only when I try to play.

[Oky]

Ummm.. how do I work out the frequency? I've recorded the sound... I ran it through a freeware spectrogram program, but I don't know how to interpret it.....



Can I find out the freq. using a multimeter?

Can I check the capacitors with a multimeter?

I can check all the earth connections for resistance... Is there any danger of shock from stored charge in the amp I should watch out for? Obviously I will have it off and unplugged...

I can send the sound file to anyone who might like to help....

thanks

Incidentally here is a pic.... (gosh shes a bit dusty...)