Marshall MG100HDFX 100-Watt Amplifier Head - Answered Questions & Fixed issues

This could be many things and unless you are electronically adept it is unlikely you can DIY the repair... HOWEVER I want you to try one thing first: Sometimes the contacts on the switches of the Effects send and return go bad leaving the input to the power amp section floating and it can feedback. To test this, plug an INSTRUMENT cable between the send and return effects jacks on the back. This bypasses the contacts, If the amp behaves, you could run it this way getting a short cable or have the amp worked on at a shop to replace the jack. The jacks are really rather poor quality on musical amps in general.

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.

If he KNEW it "just needed a fuse", why didn't he "just" replace it. Could have sold it for a lot more if it worked, The fuse is on the end of a circuit board right behind the power transformer, It should be a little glass fuse.

Pam, links below to manual, MG100HCFX Marshall Amps https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwjCloiy5YvLAhXKtYMKHYIkAjQQFggzMAQ&url=https%3A%2F%2Fmarshallamps.com%2Fwp-content%2Fuploads%2F2013%2F08%2FMG15cfx-100cfx.pdf&usg=AFQjCNEmB7ZCNRN7R5OqsRsgT3W0Utt5mA https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjj-cTY5YvLAhWolIMKHaTVDTEQFggbMAA&url=http%3A%2F%2Fwww.manualslib.com%2Fmanual%2F99252%2FMarshall-Amplification-Mg100dfx.html&usg=AFQjCNEd7UcVou-cC7zUefrpUGiGYQt18g&bvm=bv.114733917,d.amc Download Marshall Amplification MG100DFX Manual in pdf

You might need to take it to a retailer that has guitar equipment they should be able to solve your problem or have your answer

Output transistors, or output transformer.

Don't replaced anything until you jumper the power amp in jack to the preamp out jack [or effects send jack to the effects return jack]. There may only be oxidation in the contacts of these jacks. If the normal sound level comes back-either clean the two jacks or have them replaced.

Quick suggestion, Often it is the socket, usually wired to back panel. Remove chassis, clean sockets, re-solder both ends, on some Marshalls wires soldered to pins on PCB, re-solder pins as well Experience has shown this will fix 99% of this kind of problem.

Try cooling or warming it to see if it stays on for more time(for cooling) or lower (for warming)...If it does maybe the final stage of amplification (havent seen the scematics to tell you the exact component) must be overheating and stop its operation for safety and don't burn itself...You should check the power supply for correct voltages and if they are correct change this chip with a new.DONT change the IC before checking the psu because it may broke the new one too..

are you running straight off your amp with head phones? Or are you using the headphone jack as a stereo output? if just headphones. check the cord for a volume control. very common these days to have that be there. if there isn't one, check your connection so it's tight. and there will be a master volume on your amp. feel around the back panel.. they tend to blend in

Probably smoked the output IC(it is the chip mounted to the heat sink attached to the fan) which can be purchased from marshall directly or from one of their service centers. Also P-H216 sold at tubesandmore.com should work. No soldering required. Look at that IC(chip) to see if it looks burnt or has a crater on it which would indicate that that is indeed you bad component.

Try inserting a patch cable(or any 1/4" to 1/4" cord) into the effects loop jacks on the rear of the amp. If that helps you have a dirty or bad jack. A little WD-40 works wonders on corroded/dirty jacks.

it sounds like something internal on the foot switch is shorting out (or a lead wire has come off) or some where in that line , it has been severed. you can check continuity with an ohm meter. butfirst open the foot switch and just give it a visual to see if any leads are severed. you may just need to solder it back. - foot pedals get alot of winding up and unwinding. its common for something to disconnect. that would explain all the issues your having. good luck

well believe it or not. a wood block is not a bad idea. ive done it myself. it is non conductive, so you won't short anything out. to answer your question, a circuit board is layed out in several levels. not just what you see on the surface. so your problem could be internal on that particular board . So when you bend it, it then makes the connection it is suppose to. Weather it be a ground or it completes a circuit. You can use the board method , or contact the mfr and purchase a new board. Which if you choose to do that, know that handling and installing that board , you want to make sure you release any static electricity from your body before doing so. You don't want to short out the board before you get a chance to see it work.

Output trasformer is common too replace. Best OT is made by Mercury Magnetics, Weber.......

You have to use seperate speakers for each. These are not designed for any form of "bridged" operation.
You would have to wye the inouts from your source.

take it in to get fixed

Check your input (guitar signal).
Also, check your gain and volume levels.
Make sure that you have a reliable, steady, and clean power source as well.
If the problem persists, contact the store from which it was purchased. There are a lot of things that can go wrong internally with the cheaper Marshall models.

There are 2 channels, Which means there are 2 sets of knobs ... One for clean and one for crunch. Start out with a low master volume and set up the crunch, Then the clen and switch between the 2 and make adjustments until they match volume wise ... Then turn the master up.

Hi,
Looks like the main power IC is shorted!
Check the main power amp IC and replace it if there is a short between their pins!

Hope that helps you out!