Marshall Music - Recent Questions, Troubleshooting & Support

If you still want the schematics for the Marshall MG30DFX Steve I have them and can email them to you if you want

The fuse in a Marshall MG100DFX amplifier is located on the rear panel of the amplifier, near the power cord. To access the fuse, you will need to unplug the amplifier from the power source, and then locate the fuse holder, which is a small, cylindrical component with a cap that screws off. The fuse holder should be labeled with the appropriate fuse rating for your amplifier. Once you have located the fuse holder, you can unscrew the cap and remove the old fuse. You can then replace it with a new fuse of the same rating, and screw the cap back on securely. It's important to note that if your amplifier blows a fuse, it may be an indication of a more serious issue, such as a short circuit or a problem with the power supply. If you replace the fuse and the amplifier continues to blow fuses, it may be necessary to have it serviced by a professional technician.

More information required.

Why is there no sound when my wired headset is connected? To check that the headphones are connected correctly and there are no loose connections, try unplugging and replugging the audio device. Make sure that the headphones are not plugged into an audio-in or microphone jack if your audio equipment has more than one headphone jack accessible.

It's possible that your Marshall MG30 DFX amplifier is experiencing a hardware issue. The noise you're hearing when you turn it on and off could be caused by a malfunctioning component in the amp's power supply or switching circuit. Similarly, the intermittent operation of the channel switch could be caused by a problem with the switch itself or with the wiring that connects it to the rest of the amp. To troubleshoot these issues, you may want to try the following steps:

1. Make sure that all the cables and connections to your amp are secure and not damaged in any way. Loose or damaged cables can cause all sorts of problems, including noise and intermittent operation.
2. Check the fuse in your amp to make sure it's not blown. A blown fuse can cause the amp to make noise or to stop functioning entirely.
3. If the problem persists, you may want to consider taking your amp to a professional technician for repair. A trained technician will be able to diagnose and fix any hardware issues that may be causing the problems you're experiencing.

I hope this helps! Let me know if you have any other questions.

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.

"Overdrive Channel: high frequency noise as the gain and volume are increased." This is the expected result, you are experiencing feedback. Try turning the "Contour" knob all the way to the left and turn down the tone knob on your guitar.

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.

This amp has a design defect in the TDA7290 power circuit board. The heat sink is too close to main board when installed (at 90 degree angle) and can TOUCH the power signal on the board shorting out the fuse and/or transistor. I bent back the heat sink bracket slightly and it powered on fine. Also, the cooling fan must be 100% flowing or the transistor will cook in a short time, replace it also with new transistors (its a 5v computer chip fan). Good luck from Arlington guitar shop dot com.

https://elektrotanya.com/marshall_mg-30dfx_sch.pdf/download.html

You said, the best and easiest way. Since a blown fuse indicates a short, your amp will blow as many fuses as you put in it, until you remove the short. If it appears that you blew fuses, the main amp would appear to be the cause of the short. The best and easiest way to solve the problem is to take it to the Marshall dealer or an electronics repair shop. In the future, do not connect or disconnect speakers with the power turned on, and don't connect more speakers than the manufacturer recommends. The AC input fuse is inside, very near the end of the AC cord. If the glass is discolored, the fuse link inside the little fuse exploded. If it went out that violently and you replace it without repairing the short, you will get to see it blow again. The reason the fuse is inside is because in the brief second that it takes for the fuse to go out additional damage can be done in the world of solid state electronics. That's since 1972,

On main circuit board, remove the chassis

you have an open on your speaker bridge circuit

1. probably a resistor or, capacitor check with a multimeter

I know this is very old, but I have a 2006 mg30dfx and this happened to me too - it sat for years with little to no use, finally fired it up and love the OD tone, but effects were not working. I opened it up and the effects board had worked loose (popped out so it was just resting on the slot). A simple gentle push down re-seated it into the slot and effects work perfectly now. 10 minute fix.

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/%23SM_scena/Marshall/Marshall_jcm800-series-service-manual.pdf

Check that you have 15 volts across C19 and C20.

If either are bad, suspect ZD1 and ZD2 regulating Zener diodes.

Check the soldering and condition of the input jack as these are chronically bad due to damage of yanked cords.

Check for blown fuse

Power off the amplifier. Hold the AMP button while powering on. Once the screen for the reset process shows on the screen, firmly hold the STORE button to confirm factory reset until the screen shows "CONFIRMED"