Dead Marshall Amp

May 19, 2008 12:56 AM

Guitar amp problem: Marshall MG100DFX won't turn on.

I stuck this (solid-state) amp in the corner and neglected it for a while, and when I came back to it, it refused to turn on. When I give it power and flip the switch, it acts exactly as if it's unplugged. The power LED does not come on, the fan doesn't spin, and it definitely doesn't amplify a guitar.

It worked fine the last time I used it, but I was switching between two amps, so it's very possible that I left it on the last time I touched it, which would have been weeks ago. It was also plugged in to the wall directly, so I suppose a power surge might be possible. It was bought second-hand, and Marshall's FAQ says the warranty isn't transferable.

I'm guessing (read: hoping) it's a fuse, but I'd like to know whether this is something I can service myself. I've been searching with Google and on the documentation on Marshall's website, trying to find information about what kind of fuse is in there, or some sort of information about where to find it when I open the thing up.

posted by hutta to technology (4 comments total)

It sounds like the fuse. Did you try it on a different wall socket? It should be easy to fix. Once you open the amp (unplug first) it will be easy to find. It will probably look like small glass tube with a filament in it. If it is indeed a problem with the fuse, you may see that the filament is burned or seperated. Pop it out, take it with you to your local electronics store (radio Shack) or mega cool dude guitar store (guitar Center) and get a replacement with the same specifications that are written on the side of the fuse.
Stick the replacement in and turn it on before closing up the amp. If it works, screw it shut. Voila!

If it still doesn't work, it may be a the transformer or a wiring harness perhaps, but since there is no sign that the amp turns on, I think it is the fuse.

Good luck.
posted by chillmost at 1:18 AM on May 19, 2008

A lot of amps (well, all the ones that I regularly use) use the regular 3-pin kettle lead that you find all over the place. Unplug yours and plug in a different one, to a different wall socket. If it still doesn't turn on, then you've at least isolated the problem to the amp itself.

It's not a valve amp, so at least you don't have to worry about that. I'd try at a guitar-related forum, such as the Harmony Central forums. I'm sure someone more into amp customisation and repair will be able to recommend a more knowledgeable place.\

Good luck!
posted by Magnakai at 6:05 AM on May 19, 2008

Unplug it and remove the fuse. It's usually in the general area of the power cord or power switch. Look at it closely. Does is look like it's blown? Sometimes fuses fail subtly (or have mechanical defects that cause them to open), and don't exhibit obvious signs of melting. If you have access to a multimeter check the resistance, it shouldn't be more than a couple of ohms.

If the fuse is open or you can't test it, replace it with one of the same amperage. Other than mechanical defects, fuses blow for a reason, putting in a higher amperage fuse will just make whatever failed to begin with even worse. It's cheaper to replace a fuse than some high value component.

If the fuse blows again, take the amp to a shop. Although solid-state amps have lower voltages than tube amps, it's always better to let the pros handle power supply issues.
posted by tommasz at 7:42 AM on May 19, 2008

I checked the fuse with a multi-meter, and it's still good. Nothing obvious amiss inside, so I'm going to end up taking it in for service.

Thanks everyone.
posted by hutta at 11:50 PM on May 20, 2008