I have a Marshall MG100HDFX 100-Watt Amplifier half stack (solid state) and I now am not getting ANY sound out of the amp. I changed the fuse and the power module behind the fan, and still no sound, although I get a very little bit of sound out of the headphone jack when I have the headphones plugged in. What should I check next?

Output transistors, or output transformer.

If the output transistors have shorted, it is LIKELY that several others in the drivers and even farther back have also gone. HOWEVER some Marshall amps use one or more TDA7293 chips. These require installation using heat sink compound. The TDA7293 can be found at:

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=tda7293

They come in two sexes depending on which way the leads are bent for installation. You have to see how yours are mounted relative to the circuit board. Cost about $6.

Yes you can as long as the speaker impedance when paralleled doesn't go below the rating of the amp. Marshall seems to hide their design lowest output impedance. Possibly you can find that in your owner's manual. Then find the impedance of the JBL. If half the JBL impedance is equal to or greater than the lowest impedance the Marshall is rated, you are fine to use it. The speaker Watt rating should always be bigger than the amp rating which it is in this case.

If the fuse is blown make sure the reason it blew is repaired before replacing the fuse. Start the amp up after replacing it with a 100 Watt light bulb in series with the hot side of the power into the unit. This will act as a current limiter to verify it is repaired and will not blow the fuse. When you open the unit the fuse will be obvious... Follow the hot side of the power cord, through the switch to the fuse.

This is either a shorted component in the power supply section or in the power amp electronics itself. Continuing to replace a fuse MAY damage additional components. Take unit in for servicing.

They were designed to be used with the Marshall MG100HDFX heads.

Yes. You can get them from Mouser electronics at $3.42 in singles.

http://mouser.com/Search/Refine.aspx?Keyword=TDA7293

sounds like you blew a fuse.
a bad ground could've caused this.
refer to the rear of the head.
Most have threaded screw fuses.
Replacements can be found at pretty much any music store

Hello

This will help you

http://www.guitartrader.com/!OL10BXPVIk3X3pt0Y2E!BQ!/Marshall-MG100HDFX-100-Watt-Amp-Head

Thanks & Regards

it could be your guitar pickups. try using another guitar or getting your pickups waxed at your local music store. also if your playing in a small room kind of loud, or if your using single coil pickups (like fender statocaster pickups) you will definitely get a feedback noise. if that does not work let me know.