Question about Marshall Mg100dfx 100-Watt Combo Guitar Amplifier

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Mg100fx just stops making sound until its turned off for a few seconds then turned back on

This mg100fx combo works fine for about thirty min then it just goes quite. theres no popping or cracking and everything stays powered just no sounds come out. if i unplug or turn it off for about a min or so it will work for another short amount of time. does anyone have any ideas whats happening

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This looks like an overhaeting problem at fiirst glance. This shouldn't happen however. Have you had it long before it started failing? Doe it happen every time you play it, and also at low volume? If so, all I can think of is having it checked out by a technician.

Posted on Apr 16, 2014

Testimonial: "no actually not at low volumes and and i have since taken the top of the amp and it hasnt done it once since i also unplugged the speakers as the top was off and played threw headphones but again didnt do it out an hour. if it was overheating would it do it with the headphones too right?"

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  • Bump Grooves
    Bump Grooves Apr 16, 2014

    *top of amp off

  • Bob Martens Apr 17, 2014

    No, you'd have to have the meanest headphones in the world to make them overheat your amp. Try borrowing an external speaker (any with the right impedance will do), and try that for a while: if that fails too, overheating at some stage is the problem. Finding out where exactly is another matter.

  • Bob Martens May 18, 2014

    I didn't know this model had a fan... If that doesn't work that is no doubt the cause for the overheating. Keep on rocking.

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That amplifier has a tiny fan in the back that HAS to be running or the output chip (integrated circuit) will overheat. You should be able to look and see the blades turning on it. If it does not turn, take a pencil or something and give it a push. It may or may not turn freely. These are really cheap CPU fans for computers. You can find one the right size in nearly any store that sells electronic parts for computers, maybe even Radio Shack. They are measured in millimeters, so measure the old one to be sure you get the right size.
I have replaced a lot of these fans. Try to find one that says that it is a "ball-bearing" fan and it will last longer. It runs on 12 Volts.

Posted on May 18, 2014

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Posted on Jan 02, 2017

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SOURCE: we plugged it up and turned the amp on and it made

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

Posted on Sep 30, 2009

  • 916 Answers

SOURCE: popping noise

Your welcome. I'm glad I could help and if it came that way marshall should do it for you.

Posted on Apr 25, 2009

  • 5603 Answers

SOURCE: JCM2000 DSL100 No Sound

Not likely to be a fuse. The bane of electrical amps are the connectors.

Often the speaker and more commonly the input 1/4 inch connectors go bad. Sometimes caused by side loads when cables are yanked or tripped over.

Be careful of running amps IF the speakers are not connected OR have bad connectors or cables. You can arc over the tubes or pop transistors.

Get a cheap Volt-ohmeter from HarborFreight or Radio Shack and test your cables and connectors.

For a tube amp, your should find relatively low resistance at the speaker connector (certainly under 20 ohms). Do this with power off.

Posted on Sep 09, 2009

  • 5 Answers

SOURCE: marshall valvestate 8080 1. when i turn the buttons they make a cracking sound 2.when i play on it the sound becomes very quiet

As an electronics tech for 40 years I have spent half of those years reparing the damage done to electronic equipment by WD40. It is a great product when used in the correct situation. When it comes to cleaning controls in amplifiers etc the correct procedure is to apply a contact cleaner to flush out any dirt then apply a contact lubricant. WD40 contains minute graphite particles as well as corrosive chemicals. Between the two they swiftly render the controls to the bin.
WD40 great for unlocking rusty screws etc but never use it in electronic gear.

Posted on Jun 01, 2010

  • 5603 Answers

SOURCE: i was playing my guitar

Just because the voves are lit doesn't mean there is the high voltage power to the valves.

ALSO the smaller valves have TWO heaters in them and if one half has burned out that would cause the symptom. Check if the smaller 12AX7/12AT7 types all have two heaters burning. Verify that the standby switch has not gotten bumped off.

Posted on Jan 19, 2011

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