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Fried Marshall MG100HDFX! PLEASE HELP!!!
I have a Marshall MG100HDFX and a very poor solar power system. I was jammin' out the other night when the power went out so we hooked up our generator and I started playin again. About thirty seconds after, my amp took a dump and smelled like, well burnt electronics. When I took it apart, i realized that the 250W fuse was blown, so I replaced it and tried it again the next day on the solar system, not the generator, but it did the same thing again! So I hooked up the head without the shell around it to watch what happened and when I turned it on, I saw that the chip by the cooler fan, which I believe is the DFX Chip Part# TDA7293, began smoking and melting when I hooked up the power, shorting the whole thing you and blowing the fuse. If anyone can tell me a cheap way to fix it or where to buy the DFX chip, I would appreciate it. Thanks.
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Hello Rubymaster (you know those Ruby's are Chinese, don't cha ;-] )
Anyway, your only choise is to replace the TDA7293 chip. The only issue here is removing it from the double side clad board. Your best bet without any special desoldering tools is to carefully cut the IC off the pcb & then remove the leads one by one.
Also inspect the board carefully for any blown traces. You can jump any that are burned with thin wire.
the IC can be optained from any number of sources...MCM, Mouser, DigiKey, Allied (I think) for about $9.00 or so. You also want to be certain your cooling fan is running properly & not squealing. Heat is the kiss of death for these IC's.
BTW, Line6 has started adding some protection diodes across the IC to stablize it. I'm not certain right off where they go, but that really wouln't concern you if not for the unstable power source you have.
If you have trouble obtaining the IC, I would be glad to sell you one. just send me a private e-mail; glen@marsamprepair.com I get them pretty cheap from Line 6. glen -
The TDA7293 is not the DFX, though. It is in fact your power amp - it drives the speakers. Or used to. I find Mouser usually has the best price on them. A little more than $6.Education is what you're left with after you have forgotten what you have learned.Comment
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Thanks, but that all sounds like Chinese to me ;-] if you could explain all that in lamens terms, i would appreciate it much. ThanksOriginally posted by Mars Amp Repair View PostComment
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What he's telling you is that chip is what causes the sound to come out of the speaker. It is a power chip that drives the speaker and when it blows up like it did, you have to replace it and the possibly other components that were hooked up to it that also fried during the fiasco. These amps are fragile inside and moving the pcb or handling it impoper can cause further damage. Your best bet is to take it to a experienced tech if there is one nearby because sending it back could take up to six months in some cases unless your in England. If all that is wrong is the chip you could try replacing it but your expertise would go a long way in doing it right. fwiw generator power is the worst you can use for guitar amps as they fluctuate badly causing the power to be very unstable. Exactly what guitar amps do not want to see.KBComment
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i ordered the chip from digikey. it was $6.50. but i'm not quite sure how to install it. if someone could please create a walkthrough or something to show me how to install it correctly i would appreciate it much. thanks.Comment
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The chip is soldered to a small pc board. There is a screw through the tab of the chip to mount the thing to the heat sink. Disconnect the cable to the little board, and unscrew the screw. Now you have the little board in your hand - along with the white greasy goop.
Note there is a plastic washer under the screw to prevent it from touching the chip tab. Also, there is a mica piece under the IC to prevent the back side of the mounting tab from touching the heat sink. Don't lose these things.
Now you need to remove the old IC. I use a professional desoldering station. For you I recommend snipping the legs off the IC. Cut close to the IC body to leave as long a leg piece as possible still on the board. Now there are 15 legs sticking up with no IC on them. Go down the row and with needlenose pliers, grip each leg and heat the solder under it. When the solder melts, pull the leg free. Once the legs are all gone, it is a lot easier to clear old solder from the holes. SO clean the holes.
Now stick the new IC into the holes and solder it in place. I prefer to stick the legs in only just far enough for them to peek out the other side. This leaves the IC as high as possible over the little board. And that is so if I have to touch up the solder, I have the most room possible.
Now remount the thing to the heatsink and connect the cable. A smear of fresh heat sink grease is a good idea first.Education is what you're left with after you have forgotten what you have learned.Comment
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Tube amps generally have much less of a problem with power fluctuations than solid state amps. A generator that fluctuates badly isn't a very good generator, IMO.Originally posted by Amp Kat View Post
I've gigged using generators several times, and nothing happened to the amps, tube or SS. That's not to say that bad things don't happen, though.
I'd want to take some voltage readings on the generator as house loads are utilized; also with a scope to see what kind of sine wave it's putting out.
-DCComment
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ok. whats the mica thing cuz i think i may have lost it. and also where can i get some of that white goop? and the washer on mine is metal not plastic.Comment
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OH. SOme of them are not insulated, on those, the heat sink is electrically hot, but it is mounted insulated from the chassis I never remember which is which, so you likely have that kind.
For future reference, the mica insulator looks like a thin square of clear plastic, and it woulod be between the part and the heatsink.Education is what you're left with after you have forgotten what you have learned.Comment
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yeah then i think i lost the mica piece...Comment
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If your heat sink is insulated from the frame, there never was one. The mica would have left a square impression in the grease, and that would be slightly larger area than the chip itself. If there was no insulating plastic washer under the screw, that is firther evidence there was n0 mica.Education is what you're left with after you have forgotten what you have learned.Comment
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ok. now where can i get some white goop?Comment
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Try Radio Shack. Note the blank stare when you ask the cell phone sales droid for "silicone heat transfer compound".Originally posted by rubymaster92 View Post
-DCComment
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mg100hdfx power amp board
If you call an authorized Marshall dealer, and they are "interested in helping you", they can order the complete little power amp board with chip on it for about 20.00 so good luck. You can find a list of authorized dealers on the Marshall website and don't even try to call them and order the part directly because they'll just refer you to either a service center or a dealer. this board should just plug into the mainboard and mount on the heat sink on the back of the chassis and if it doesn't come mounted on a heat sink then DON"T FORGET to apply THERMAL PASTE to the back of the ic chip between chip and heat sink.Comment
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