Monitor buzz One of the monitors will buzz when power connected (no signal cables connected) seems like a 120Hz buzz from speakers.When power is turned on, it virtually goes away but is barely audible. Buzz is louder when amp is cold, after warmed up and switched off, buzz will not be audible until amp cools. Suspect worn filter cap / diodes? Suggest any parts to throw at it before paying diag fee and having monitor tied up at repair shop for weeks?

SOURCE: loud buzzing when amp connects to guitar

The buzzing noise could be caused by a grould feedback loop. This occures when the amp is plugged into one power socket and the guitar's amp is plugged into a drifferent power socket.
Try to use a power board, plug in all your devices into this power board and plug the power board into a power socket.

SOURCE: won't do anything but buzz very loud

The input or the CD input jacks may have a bad solder joint on the circuit board. If the amp is still under warranty, take it in to be serviced. If not you will have to have someone work on it. If you do it yourself, make absolutely sure there is no power running to it. Also be aware that the filter capacitors in the power supply can retain a dangerous charge. Sometimes you can discharge these by unplugging the amp from the wall power while it is on with the volume very slightly turned up. Once you have the circuit board out, you can wiggle the jacks and see if they feel loose. Look at where they are soldered to the board to see if they need to be resoldered. If that is not the problem then you will need a schematic and some troubleshooting experience and tools. Hope this helps.

SOURCE: Buzzing fan on a Marshall mg 100 head

Try to remove the fan and look for the sticker on the back side where the wires come out.

Remove the sticker, underneath it there will be a small aluminium cap (sometimes there is no cap and the axis is readily visible when you remove the sticker).

Take the cap off with a sharp tool (it shouldn't require a lot of force to do it), now you should be able to see the fan axis being held in place by a small clamp - put a drop or two of machine oil in there, move the fan blades a little to make the oil flow past the axis into the bearing.

Reinstall the cap, put the sticker back in place, reinstall the fan and test it.

Sometimes this will make things better, but if it doesn't then it is only fair to replace the fan.

regards

Triarcuate

SOURCE: alesis prolinear 720 powered monitor stopped working

Yeah. I think you should listen to that guy, Lamar Barton.

SOURCE: Fender vibrolux. Very (loooud) loud hum/buzz All

Here is the schematic:

http://elektrotanya.com/fender_vibrolux_6g11_schem.pdf/download.html

Check the quality of the DC bias as being free of ripple.across teh 25 mfd/50v cap filtering the bias.
If much ripple there, replace the cap. Also the .05 bypass on the swinger of the intensity control.

This should be an easy fix, but you might need an oscilloscope to diagnose it quickly... or just parallel caps across these to see if it kills the hum.

The main high voltage filter caps are also suspect as well as the bypass of power to the ealier inverter stage a 16mfd/450v

There are lethal voltages in this so use great caution when troubleshooting... the caps hold a nasty charge.