Marshall MF350 Mode Four Died, please help!

[JackAttack]

Hello! Well I've had my Mode 4 for about 3 or 4 years. I love it. I've toured across the country with it and had no problems at all. Today the amp was in use, then abruptly died and lost power. There was a strong smell as if something got fried but there was no smoke (that we could see). The head will not power up at all and i looked at the two tubes. They looked fine. So, I'm kind of at a loss. I'm not too familiar with trouble-shooting electronics so I don't know where to begin to try and repair it. I have some buddies that are qualified to work on it but I need some help figuring out what to do. Please Help!!!

[Enzo]

I will bet my lunch money your output modules are burnt up. And they then popped your fuse inside. You will need at least four new TDA7293V ICs and a bunch of good luck.

I am glad you got good service from your amp, but I have to tell you, I no longer accept those for repair in my shop. Too hard to keep them from blowing up. ANd I don't like to put my name on repairs that will blow up again.

If you bought it new, it should have some warranty left, though probably only on parts. In that case, take it to an authorized Marshall repair shop for warranty repair.

[JackAttack]

I see, I pretty much expected something like that was the case. In case my warranty is expired, I'm pretty sure it is, can you steer me in the direction of some tips on how to repair it? I've got experienced friends that would be undertaking the task, I'd just like to be able to offer them a little help if they needed some technical information. Thanks for your time man.

[mensur]

I see, I pretty much expected something like that was the case. In case my warranty is expired, I'm pretty sure it is, can you steer me in the direction of some tips on how to repair it? I've got experienced friends that would be undertaking the task, I'd just like to be able to offer them a little help if they needed some technical information. Thanks for your time man.

You will see the 4 chips on the small boards, they only need to be replaced.
You must desolder the old ones, and solder the new ones.You don't need to bias or anything, except you must be very careful with soldering.

[Mars Amp Repair]

Agreed,
However in this amp as Enzo mentioned, they are very persnickity & your best bet is to just bite the bullet & order all four the IC boards complete. Replacing the individual IC's is tricky & time consuming. If there are any blown traces you'll need to be able to repair them.

One false move or solder splash and KAPOW!!!! All FOUR ic's will blow again. you can search the forum for prior posts on the aptly named Mo-Fo 350.

glen

[JackAttack]

Thanks for the tips. Before I do any of that, is there a way to trouble-shoot to see what the problem is exactly? There isn't anywhere around where I live to send it to, and I'm definitely not shipping it away to get it looked at. I'm not saying that you guys are wrong, I just want to know exactly what's going on with it before I order some parts that may not be the issue. Thanks again fellers.

[JackAttack]

Also, I don't know if this helps any, but the burnt smell was pretty strong yesterday and couldn't narrow it down to where it was coming from, but today is seems to be coming from right around where the tubes are, but as I said in the first post, both of them are fine. I don't know if that's the area you guys are talking about, with the IC's. I'm having trouble finding those too, not really sure what they look like.

[Enzo]

There are four identical little modules - tiny circuit boards maybe 2" long by 3/4" wide - and each has one 15 leg IC soldered to it that looks like this:


There will be a multiwire cable to each little module coming up from the main board. Each module is screwed to the heat sink.

[Mars Amp Repair]

You can also unplug ALL 4 power IC modules to determine if they are blown. Replace the blown fuse & fire it up with ALL FOUR unplugged. If the fuse doesn't blow and all seems to function ok (no sound to the speaker of course) you at least have the answer to the status of the power modules...they're blown.

Not sure if mentioned before, but you MUST replace ALL 4 modules. One bad blows the other four.

Also be very careful when removing the 15pin plugs to the modules. Only rock them end to end as slightly as you have to, to get them to come off.

give the power IC's a good visual. Quite often you can see a bulg or crack in the front surface of them. also sometimes you can see where they spewed their guts between the IC legs. that's a good indication that they are blown. glen

[Gtr_tech]

These things have a bad track record. If you *love* it that much, I'd just unplug all the amp IC boards, leave it that way and put it back together. Get a PA pwr amp and use the line out/effects send and run that into the PA amp. At least it won't blow up constantly....

[Enzo]

I rarely find myself calling anyone for advice on guitar amps, but one of my favorite experiences was when I called Korg and talked to their Marshall guy about these MF350s. I asked why they liked to blow up so much, and what might I be missing in their service. His response was that I was missing nothing, they like to blow up, that is just the way they are, and that was why Marshall quit making them. Wow.

Considering all the available, very reliable power amps for not a lot of money, I think Gtr_tech's idea is a good one.

[Gtr_tech]

That'd be my plan of attack. A SS pwr amp is a SS pwr amp for teh most part (as long as its not IC based), and they won't even break a sweat doin' guitar amp duty. Saves them mode 4s from be'n a doorstop. I don't use any SS amps myself, but if I did it would be pre-ROHS and all discrete for the output section.

[Alex R]

On the other hand it can be a thoughtless, soothing Zen task repairing these. You just keep soldering new ICs in till they stop blowing up, there's nothing at all to think about except getting the old ones out and and the new ones in, firing them up and waiting for them to pop again, until fortune smiles and they don't. Your mind usually gets really really pure before that happens.

Somebody on here advised me once to put a VM on the output and just tickle the variac up a teensy bit at a time at a time, and stop if you see any kind of appreciable DC. It works - that way if you left a solder bridge or something you don't lose four more ICs and an hour or two of soul-cleansing finding out. But yes a few bipolar discretes are a heartwarming sight.

[JackAttack]

Thanks for all the help! I've located the ICs and one of them does have some blackening that I can see on it. I never really believed anyone about the Mode 4's blowing up, mainly because I've owned it for 4 years and toured heavily with it for 2 of those with no problems. The PA power amp suggestion is quite genius, I will put some thought into that. All is well though, I'm playing on my drummer's Mesa Boogie stack until I can buy another head. This Mode 4 will not become a doorstop. It will see some action again.

[Alex R]

The Mode Four gets a bad rap mainly because it is a royal pain to fix, and keeps blowing up and eating up an honest technician's stock and time. As an amp it is probably pretty reliable. Till it isn't. Like any other amp. Getting it fixed is likely to be a bad deal for the tech, thus may be a good deal for you... shit why did I say that? No, in truth, once it has blown up one it may well do so again. The power amp idea is the way to go.