Marshall MG50DFX level problem

[andymac]

Hi all

I have a MG50DFX that is having an issue with its levels. When playing, it'll sound fine, but then occasionally the sound will cut out - not suddenly, but as though someone has hurriedly turned the volume pot down. This persists for an intermittent amount of time, and no amount of "power cycling" or pot twiddling will get it out of its rut. Occasionally you can hear the guitar or 'lead tip buzz' coming through the speaker, but usually nothing.

If it reverts to normal while i'm playing, it is again a gradual return as though the volume pot is being turned up. Does anyone here have any suggestions? I've taken it to a repair shop who charged me ?30 just to look at it, but couldn't find anything wrong with it (damned intermittent faults!). I've been living with it for some time now, but it is just getting too annoying, plus I will be gigging with it again in the not too distant future.

A few points:
1) It's not the lead - tried with several leads and they work with other amps.
2) It's not the guitar - again tried several with other amps.
3) No sound comes out of the emulated headphone jack either.

Thanks all - i realise this is my first post, but I've only found this community in trying to search for an answer! The forum looks interesting, and I'm sure i'll have stuff to contribute as well.

Andy

[52 Bill]

I have a MG50DFX that is having an issue with its levels. When playing, it'll sound fine, but then occasionally the sound will cut out - not suddenly, but as though someone has hurriedly turned the volume pot down.

Andy: Welcome to the board. Sounds like you have checked some of the simple things, which helps a lot. Often times the symptoms that you describe are caused by mechanical problems.

If your amp has an FX loop, have you tried to plug in a spare cable bridging the loop? Same thing with a pre-amp out to power amp in loop?

Have you tried to give the amp a good thump? Turn down the reverb before you try this one. When it cuts out, give the amp a good slap on the top and maybe each side as well, and see if you can reconnect a bad connection. If the amp responds to this, then there is something loose inside and it will need to be opened up.

[andymac]

I haven't tried the FX loop bridge - I'll give that a go tonight (I don't actually know if it has one - I've never used it if there is!).
As far as the percussive maintenance goes, I found that seemed to help in the past, pointing at a loose connection somewhere. This has stopped working of late though, probably suggesting that the loose connection has worked its way too loose.

Another thing which I forgot to mention was that sometimes a sudden change of input brings the signal back - i.e., the 'pop' when plugging the guitar in, or slashing out a power chord, but again this seems to be failing.

Thanks for your reply - if anyone has any suggestions about how to go about finding the loose connection (if that's what it is), I'd be very grateful to hear them - I'm not hugely experienced when it comes to electronics (I did a bit of DIY-stompboxing a couple of years ago, but I haven't had time for it of late!)

Andy.

[52 Bill]

As far as the percussive maintenance goes, I found that seemed to help in the past, pointing at a loose connection somewhere. This has stopped working of late though, probably suggesting that the loose connection has worked its way too loose.

Check the FX loop thing first, because if there is a problem there, it will often respond to "percussive maintenance". If that doesn't cure it, check out R.G.'s troubleshooting page at Geofx. He goes into great detail on finding loose stuff and other simple problems.

[andymac]

Wow - that FX loop bridge seemed to work. With no signal coming through, I plugged in a patch lead - hey presto, signal came through fine. Unplugged FX bridge, signal stopped. Having repeated a couple of times, the FX bridge is currently not needed to get the signal through, though I'm sure this hasn't fixed the problem for good.

Is there any reasoning behind your suggestion of the FX bridge, and does this help to diagnose the root cause of the problem?

Thank you so much!

Andy

[52 Bill]

Is there any reasoning behind your suggestion of the FX bridge, and does this help to diagnose the root cause of the problem?

This is a very common problem with lots of amps. There are contacts on the loop jacks that are normally closed, bypassing the loop. If these contacts become dirty or oxidized, they will no longer make connection and will cut off the signal from bypassing the loop.

To cure this problem, you will need a spray can of contact cleaner, like Deoxit. Start by spraying just a little in the front of the two jacks. Then plug a cable in and out of each jack a few times.

If the oxidation is not too bad, this will clean the metal contacts and you will be ready to go. If the oxidation is really bad, you may have to open up the amp and physically clean the contacts to restore the signal. I find that this is only needed when the amp has been exposed to really harsh environments, like smoky, greasy bars, etc.

[Enzo]

Usually they clean up, but once in a while you actually have to replace the return jack. And also check the solder under the jack for cracks.

[andymac]

Thanks guys - that's awesome! Now to see if I can quiet the fan noise at all (it's not a fan fault - the MG50DFX in the shop makes the same noise, it just a 'whooshing' of air - i guess i just need to improve the airflow)!

Thank you again!

Andy

[plankmonkey]

Ello all,

Just wanted to post a big thank you to everybody that responded to this thread as I have the exact same problem with my mg50 and this has sorted it out!!! So cheers everyone

plankmonkey

[dreamer67]

same here. Got this problem for years now. It was juste getting worse. The problem is solved and that's a good thing. May your path be full of rose petals and your name blessed over 7 generations.

[Sled Ed]

Another Huge Thank you from me; I thought I had popped my speaker, and was ready to spend money I don't have on a Vintage 30 speaker to repair. Imagine how upset I would have been when that was not the problem?? Should I still go for the V30 in the future now that it is fixed?? Sleddyyyyyy