Marshall MF350 Mode Four - No power up

[NoCurfew]

Well I've gone and screwed up...

I was trying to replace the AMP2 fan on my MF350 because it was making a lot of noise. I ended up forgetting to unplug it and touched the back panel wall with the heatsink... a little tiny spark...

i figured maybe all is well still, so I unplug, keep working and put in a replacement fan (not stock but figured it would work... although it's a 12v instead of the factory 24v ones)...anyway I finished the fan install and powered up.

POW!!!!! and A BUNCH OF SMOKE COMING FROM THAT HEATSINK AREA!!!

Damn. I guess I probably blew an IC (what does that stand for anyway!!!) based on what I've read on this forum. I can see dark staining on the legs of one.

First off, where the heck is the fuse on this thing?

Second, I noticed the IC chip is soldred at about 15 spots to the little board it's attached to... If I change the IC's, do I have to de-solder all those, and rede it for new one? or will the main part of the IC slide off and leave the legs attached to the mini board?

Third, who is this "Mouse" i keep hearing about who sells stuff? By the looks of it, I need 4 new IC's and 1 new 24v fan.

Go&&am it!... All of this because of a noisy fan....and me being brain dead.

[Am Peg]

Whew...

Well, without knowing ohms law, calculating power factors and so forth, it's never really a good idea to arbitrarily replace parts of differing values. For example, a 24 volt fan may consume 1/2 amp resulting in 12 watts of power consumption. A 12 volt fan may pull 2 amps or 24 watts. Boom. Plus, the power supply was specifically designed for 24 volts.

Sorry to say, but the 24 volt supply is probably gone - or whatever voltage regulator / zener stack / whatever. There may be more problems from initially shorting something on the heat sink grid. Hard to tell without a schematic.

An IC is an Integrated Circuit. Could be an Op Amp - could be a voltage regulator, could be a microprocessor. It's an IC.

Mouser is where you'll likely go shopping for new parts.
Mouser.com
Good luck.

[Enzo]

Actually the 12v fan won't hurt the 24v supply, either type fan doesn't draw that much current. However it means the 12v fan will be running on 24v, spinning twice as fast as normal, and who knows how long it will be happy doing that.

IC does mean Integrated Circuit. In this case it refers to those 15 leg things, but there are all kinds of ICs. The 15 legs are part of the IC, like your legs are part of you. They have to be unsoldered from the little board. They are type TDA7293V. Most places do not stock teh TDA7293H version, but if they do, ONLY get the TDA7293V version. The H version is made for horizontal mounting and its legs will be the wrong length.

www.Mouser.com is a large electronic parts supplier many of us use. They usually have as good a price on the 7293s as I find around.

The fuse is on the main board along the rear wall.

Now the sad news. If one of those power ICs blows - and black soot coming out is a sure sign of blown - you must replace them ALL, all four.

[NoCurfew]

Enzo,

I'm glad to see you on here, because all the other MF350 threads I've seen, you were the guy with all the info!

I am going to put in an order at mouser.com for 4 of those V ones. I know a guy pretty well who should be able to solder these in correctly. I would just screw it up.

Aside from the Fuse which may be blown, are there any other areas of concern?

Also, I would like to find a direct replacement for that 24v Fan on there. Any idea how to get my hands on one?

Jesus when I'm done with this I'm getting a JVM.


Thanks

[Enzo]

I just buy the 24v fans from Marshall (Korg USA), but I am an authirozed service center. Any Marshall dealer could order you one, and isn't there a Marshall Parts site somewhere? Parts is parts, maybe?

[tonechaser]

Where are these IC's located? ie. R? Thanks!
tonechaser@rocketmail.com

[Enzo]

If you mean the TDA7293 ICs, they are each on a small circuit board, and they are screwed to the heat sinks individually. Multi-wire cables run from the small boards down to the main board.

[tonechaser]

Thanks for responding! I bought it for $60.00, hoping for an easy fix. When I opened it up tonight, I discovered that someone had removed one complete unit including the heat sink and the fan. They removed one circuit board from the other heat sink. Do you know where I can get replacements? Thanks again!

[rf7]

Thanks for responding! I bought it for $60.00, hoping for an easy fix. When I opened it up tonight, I discovered that someone had removed one complete unit including the heat sink and the fan. They removed one circuit board from the other heat sink. Do you know where I can get replacements? Thanks again!

As Enzo said above, try Korg USA, your local Marshall service center, or parts is parts on the web.

[Enzo]

Fender Stratocaster Parts,Fender Telecaster Parts,Fender Bass Parts,Marshall Amp Parts, Guitar and Amplifier parts,Gretsch Guitar Parts,Gibson Guitar Parts, Hofner Bass Parts. Parts is Parts has more Guitar parts and amp parts.

[BurrMan]

If you mean the TDA7293 ICs, they are each on a small circuit board, and they are screwed to the heat sinks individually. Multi-wire cables run from the small boards down to the main board.

Any help with where I can buy a power transformer for the MF 350? I have one thats a 230V~50Hz Dagnall TXMA00110 and I live in the US. Instead of purchasing a stepup/down box, I would like to look at just getting a 120V one and wire it in?

Funny enough, the back panel where the plug inserts, list the 230V~50Hz, but it's just a sticker covering the printed 120 stuff. I am assuming that there is nothing else different on the amp from the transformer wires on....

I would appreciate any input you have. I have gone to all the links I could find selling transformers and nothing is listed. I guess the next step would be to call them, though I thought I would ask here. I have also read that you dont want to work on them and the other info you have posted.

Thanks,
Burr

[Jazz P Bass]

The schematic indicates that the switch & the fuse change when you go to 110Volt.
I got this info on the transformer that you need.
"117volt 50/60hz..TXMA 00097..D2782 Batch:0706046F...Dagnall Electronics Ltd..output 18volt & 32volt on secondary"
Marshall Transformer Power, TXMA00097 | Marshall Transformers | AUTHORIZED NATIONAL PARTS DISTRIBUTOR FOR KORG, VOX, BLACKSTAR. PARTS FOR FENDER, GIBSON, GRETSCH, HOFNER, SWR, GUILD...

[BurrMan]

The schematic indicates that the switch & the fuse change when you go to 110Volt.

Thanks for the comeback! I saw the info on the fuse. "The switch"? Is this the red power switch on the exterior? or is it a component on the inside. I need it to be simple.

[Enzo]

The main power switch is a rocket, yes? And it would lite up. They have two different part numbers for 120 or 240v use, because the inner light bulb inside the switch is set up for either 120v or 240v. If you leave the old 240v switch in there, when you use it on 120v, the bulb will either be super dim, or just not light at all.

[BurrMan]

The main power switch is a rocket, yes? And it would lite up. They have two different part numbers for 120 or 240v use, because the inner light bulb inside the switch is set up for either 120v or 240v. If you leave the old 240v switch in there, when you use it on 120v, the bulb will either be super dim, or just not light at all.

Thanks.... Can you confirm the power supply listed above? There is a slight difference from "19V" as is now, to "18V" showing there. Just wanted to be sure (No disrespect)...

Thanks again for the responses.
Burr