20 Most Recent Marshall Amplification Marshall MG102FX 100 Watt 2x12 Combo Guitar Amplifier with FX and MP3 Questions & Answers

NEVER CONNECT PEDALS THROUGH THE EFFECT LOOP OF AN AMP. They are NOT design to work at the same signal levels !!! ONLY use effect units that are design to be used in amp effects in the amp effects loop/

Hi there
Firstly don't panic! It might be something quite simple - and it might not actually be the amp that is at fault.. Here are a few things you can try to start with to trace the problem by systematic elimination.

1. If you are using any effects pedals unplug them and plug your guitar straight into the amp - does that solve it? Turn off any built in effects on the amp and unplug the foot pedal.
2. Try a different guitar lead - leads are very prone to failure -especially at the solder joints in the jack plugs - but sometimes in the middle as well because they get pulled a lot in use. The tiny twisted copper wires in the core of the lead can become cracked, which will increase the electrical resistance (causing the volume to drop. As you move about the bits of broken wires may touch again (reducing resistance so the volume increases again).
3. Check the tightness of the screw threaded rings (bezels) that hold the jack sockets on to the body of your guitar and the front panel of your amp. These can work loose over time (especially on the guitar) and cause the jack plug to only make a partial contact inside the socket with the same results as no 2 above.
4. On both the amp and on the guitar quickly and vigorously rotate all the volume and tone control knobs backwards and forwards (up and down) fully several times - the copper contacts inside the knobs can become oxidised over time. Doing this will clean them a bit by means of the friction between the contacts. Do this with one knob then test to see if the problem has been resolved before moving on to the next knob - that way you will be able to identify which one is faulty (you may hear some crackling as you rotate it). In the same way flick your guitar pick up selector switch backwards and forwards several times. If you find this resolves the problem you might apply a VERY little squirt of switch cleaner ( a spray that you can buy from electrical component shops like Maplin) to give the knobs / switches a more permanent cleaning - but don't overdo it and allow a few hours for any surplus to evaporate before you use the amp again. HOWEVER - don't use switch cleaner if your amp is still in manufacturers warranty AND if rotating the knobs hasn't solved the problem.
5. If none of the above has solved the problem then the amp itself might be faulty. Don't attempt electrical repairs yourself. Apart from the obvious danger of messing with electricity you may actually do more harm than good and without proper test equipment it is extremely unlikely you will be able to trace a faulty component. If the amp is still in warranty take it back to the shop (or phone/email them if you bought it online). If it is out of warranty your local music shop may know of a good repairer in the neighbourhood who won't rip you off (they may even have their own 'techie' who can do it for you).

https://www.dropbox.com/s/6spu98r39t2wvcr/Marshall%20G30RCD%20Schematic.pdf

First check the preamp valve in that curcuit

Hi. Doesn't look like it as the speaker is a 4 ohm one and the head needs at least 8 ohm as far as I can see.

https://www.manualslib.com/manual/99237/Marshall-Amplification-Mg15msii.html

Make sure speaker cable works and is connected then check fuses. If it has a master volume, make sure it's turned up.

Most likely cause for this is an intermittent potentiometer. Check to see if any of them are mechanically loose as this is a sign that they have been damaged and could have cracked the wiper surface inside the pot causing this problem. Alternatively, any switch that controls any gain setting could also be intermittent or dirty. Gain of the amplifier should be stable, but is controlled by the feedback and signal injection at the pots so that is where to look first. Good luck, as intermittent problems are tricky, but sometimes better than no function at all which can be more costly.

What type of Marshall, please? First of all, control the fuse and let me know.

clean switch connections

Does anything happen while you turn the knobs on the amp? I had a similar problem with a yamaha amp. It turned out a couple of knobs went bad. Soldered new pots and it works fine for me now.

No, the ATV50 head is rated for 4 ohms total. Using both 4 ohm cabinets at once will fry your amp. Your only option would be to rewire your cabs internally to 16 ohms each by connecting the speakers in parallel, but that would cut your amp's power in half.

No, the ATV50 head is rated for 4 ohms total. Using both 4 ohm cabinets at once will fry your amp.

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