Marshall MG50DFX no sound on CD, main input, or FX return.

[mab81t]

Was playing last night and the volume just gave up.
I hook up the fx send or the line out/headphones to another amp and it works fine, and the signal is strong, but when i plug the lead back into the fx return I get nothing. Same with the CD input... nothing.
The speaker is fine because I used another amp to power it too.
Any ideas?
I suspect it's got something to do with the main power amp but have no idea what to check with the multimeter

[52 Bill]

Welcome to the place.

I suspect it's got something to do with the main power amp but have no idea what to check with the multimeter

Based on your description, the problem is in the one of two places, the power amp or the master volume circuit. While it can die in many ways, the power amp chip usually goes out with a bang and will normally cause the main power fuse to blow. So if the amp still powers up, that may be a good sign.

When you turn on the amp, can you hear anything coming from the speaker like hum or hiss?

Oh yeah, this amp uses the power amp modules that are really problematic. They seem to blow up if you look at them wrong. A few suggestions are to not plug or unplug the speaker while the amp is turned on or has been turned on recently. Do not plug or unplug the power amp module unless the power supply has been discharged. If you need to purchase a replacement power amp board, check it before plugging it in, as there was a batch of boards made with the wires connected in reverse order.