upgradde

Hello everyone. I bought, used, a Marshall MG100HDFX head and matching cab about 2 weeks ago. I had a gig last weekend and brought out my early nineties crate 4 x 12 extension cab to make her a full stack.

I had been playing it all week in practice with the master volume around 3. During sound check, it was making an awful, indiscernable chirping, screeching sound. After checking my connections, I changed my instrument cable and unplugged the footswitch, for some reason it worked fine for about 5 minutes.

I cranked it up to 5, played about 2 minutes of one song, and it blows and powers off. I could smell smoke, took her apart, fuse is fried. Keep in mind I know nothing about electronics. I put in another fuse, switched it on, blows it. I unplug everything, try another fuse, turn it on, blows it immediately and see some smoke come out of the fan unit.

I have since taken it to the local shop for repair.

I have a few questions perhaps you guys can answer. I researched this amp extensively after this happen and see this is a somewhat common problem with this model, is that true? Second, when the tech opened it, he asked me if I had done anything work on it prior, I said no and he said it looked as though someone's already been in there as the white glue on the fan was amateurly done.

Now I don't know if this amp is just flawed, or if perhaps I did something myself to it. The Crate extension 4 x 12 is only 4 Ohms. The Marshall is 8 Ohms, could this difference have blown the fuse like that? Is there a reason it would work at Master set to 3, but not 5?

I'm really lost here and sadly don't know much about electric.

MG100

Hi

Heads up (sorry - awful pun!) if you hook an 8ohm with a 4ohm cab to the amp, the load is 2.6ohm. The amp is not designed for less than 4ohm. The more you turn up the volume, the more you are likely to damage the amp in this scenario.

The white glue your tech is talking about sounds like heat seal compound that you might (should!) see where the tab on the IC on power amp PCB attaches to the cooled heat sink unit. I'd epect to see some spillover. If he thinks its glue I'd wonder if he's experienced.

Stick a set of head-phones into the jack / run the FX send directly into the FX return of another amp - if this works fine the chances are the problem is with the power amp section.

I had a problem with my amp generating a terrible racket (and that wasn't just my playing...) that was fixed by replacing IC1 (TDA7273 - costs about €6. (I didn't have any problems with the fuse)

Whatever you find works please post an update so we learn

Hope it helps

Paul

djmguitarist

Hey this should be an easy one, i have a mg100dfx amp and the fuse blew in it and i don't know what size fuse to buy or where to get it? any info could help, Thanks..

-Daniel

Kane17

You should be able to open it up and see it. There's really not much in the MG's so it should be really easy to see right away. I have the head version and there's only 4 screws that need to be pulled out in order to seperate the entire amp from the box. The fuses specs should be right on it..It looks like a common fuse you should be able to get at radio shack or something (but I haven't looked at the specs). In any case if you bring the fuse in to any electronics shop they should be able to get you what you need.

ernesto786

i have a similar problem, my mg 100 hdfx also blows fuses instantly, my friend was playing it and it just stopped, changes the fuse and it just blew in second. when the third fuse blew some smoke came, i couldn't see it just smelled a burnt smell. i read the reply but I'm not sure what an IC1 is to try if that would fix the problem, I'm new to electronic hardware. can someone tell what it is or where i could find it? tried google came up with nothing. thanks