Question about Marshall Mg100dfx 100-Watt Combo Guitar Amplifier

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Hi i am john... i have a 100dfx mg series... it is

Hi i am john... i have a marshall 100dfx mg series... it is blowing fuses... its tranformer is needing replacement... i need to get a new one for this amp . who can set me up? thanks john

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There are MANY more likely components than the transformer that will cause the fuse to blow.

Most common are filter capacitors, rectifier diodes, and shorted components in the power amp section.

Transformer failure is very UN-likely. Have a competent electronic tech troubleshoot the unit.

When testing the unit, put a 150 watt light bulb in series with the power line... saves fuses during troubleshooting. This limits the current so one can analyze the real cause of the problem.

Posted on Jul 13, 2010


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Marshall MG100HDFX footswitch toggling - bypassing?

I once used uART & some latches to decode & hold the difference between "odd & even" midi program changes. Then used the output to switch a relay in a twin necked guitar to change between necks as it were in response to a midi pedal. Perhaps you could do something similar? Else get a Studiomaster MA-36 midi analyser & hack into it to use one piece of midi data (from across an LED?) to switch channels on your amp? Good Luck!

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Marshall Mg 100DFX power on no sound it just cut out last time i played it.The fan has issues I wonder if there is a cooling sensor shutting down the amp output.I thought solid state amps were bullet...

Something has probably failed or become a bad joint. If you turn up the gains and volume to max is there any hiss or hum from the speaker? If not there will be a problem in the power amp or power supply. Check fuses at back. The speaker may be open circuit too, that is easy to check with a multimeter. If you can't get far yourself, you'll need a repairman.

Solid state amps are not that reliable these days, there are so many things that can fail due to all the effects that people demand to be built in. Look at how many people are reporting problems with ss amps here.

Apr 02, 2011 | Marshall Mg100dfx 100-Watt Combo Guitar...

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I have the old 3520 200w SS head. It is blowing the fuse as soon as I power up. No one around here (south of Dallas, TX) know anything about this amp. I am using the Marshall 1553 cab w/ one 15"...

Here is a link to your schematic:

Scroll way down and click on "Get Manual" link. They will only let you download two a day unless you are registered.

Suggestion is to troubleshoot and repair the unit.

You will likely find one of the following:

Shorted transistors in output TR5 through TR10

Shorted rectifier diode(s)

Shorted fillter capacitor

Shorted power transformer (not very likely)

Mar 21, 2011 | Marshall Amplification Marshall Mg Series...

1 Answer

Hi i have the Marshall MG15FXMSDM Dave Mustaine Megastack and i also have the programmable footswitch. the other day, i was plugged into a big surge protector and the footswitch was working fine. i...

First thing is to verify the MAIN power source is getting to the amp. It may not be the fault of the footswitch at all. Connectors and cables are the usual cause of these problems. Seating of connectors is a common problem...

Mar 02, 2011 | Marshall Amplification Marshall MG Series...

1 Answer

So, i think I've blown the fuse in my Marshall MG 100 HDFX head (I tried to run 2 speaker cables out of the head into a quad...stupid >.<). What type of fuse do these heads use? How can i access...

The fuse is inside the unit so as to force you to open it and look for damage.

The fuse is likely a 3 amp/250 volt type.

Replace the fuse and then put a 100 Watt light bulb in series with the hot side of the power input. If the lamp stays lit with no load on the unit, then there is damage that requires repair before use. If you just replace the fuse repeatedly you may damage further components.

In the future obey the minimum resistance load on your amps.

Aug 22, 2010 | Marshall MG100HDFX 100-Watt Amplifier Head

1 Answer

I was playing my Marshal 100DFX for about half an hour and when I was done it smelled like burnt electronics. Then I noticed the fan wasn't working. It usually turns on right when I turn the power on. I...

Replace the fan with an IDENTICAL part. Do this before using the unit again.

There is a possibility that the fan is controlled by temperature and the failure is actually with that electronics rather than the fan itself.

May 19, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

Marshall GM 100DFX is blowing fuses

Probably one side of the power amp has shorted and there is likely several semiconductor transistors and other components requiring replacement, but this amp uses a stick IC power amp.

Copy/pasted from the music forum between the arrows, this is likely the problem in your unit:

>>The schematic is posted in the Enzo gallery at

The 15 leg power IC on the heat sink is a TDA7293V - it is the power amp for the unit.

The chip with small board attached can be ordered from any Marshall dealer or from places like

I usually buy my 7293s from Mouser. They currently have 622 of them in stock and they sell for $6.48 each. Probably won't run out of them soon. << Hint for you: When powering this up after repair, insert a 100 watt light bulb in series with the line cord into the unit. This will act as a automatic reseting fuse which will save fuses if you haven't got all the "cancer" out of your failed amp. It will allow you to do troubleshooting by limiting the current to a safe value. Also, when replacing the TDA part, be sure and use heat sink compound under it and if an insulator was used, make sure you replace the insulator. ALSO clean the area of any soldering residue and flux BEFORE powering the amp again.

Jan 13, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

Hi,I turned on my Marshall mg series 100 dfx and there is no sound,just static comes on.Its starts with a kinda bad feedback sound than turns to loud static.

I suspect the power supply for the effects processor has failed. The effects unit will "go crazy" when power supply is too low voltage.

If the amp has loud noise, then the power amp portion is PROBABLY OK.

I had a similar problem in a Behringer amp caused by a bad electrolytic filter cap.

Aug 11, 2009 | Marshall Mg100dfx 100-Watt Combo Guitar...

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