Marshall Amp repair HELP!!!

  • Thread starter Thread starter timboZ
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timboZ

timboZ

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I have a MG250dfx that is blown

I'm looking for a schematic or a marshall PN for the boards that mount to the heat-sink/fan.

I replaced tha amp IC's (TDA7293v) that were bad but I think the caps are bad as well. I can not read the info on the caps to replace them.

Thanks.
 
for a second i was worried that you were trying to repair a tube amp yourself..

cant get a schemo from marshall's site?
 
just put caps in that you are sure have as high or higher voltage and cap ratings as the existing ones an you should be ok. Actually, don't even replace them, bridge the ones that are there and see if it solves the problem.
 
dragonworks said:
just put caps in that you are sure have as high or higher voltage and cap ratings as the existing ones an you should be ok. Actually, don't even replace them, bridge the ones that are there and see if it solves the problem.
Click to expand...

sounds risky.

take it to a music store, other than guitar center/sam ash of course, cause they wanna charge you $80 to open it up usually.

i have an awesome tech if you are located near shirley/mastic/manorville NY, and he does it cause it's something he loves, not for a living :eek: :D

i love that guy.
 
i've never worked on that modal so take with the proverbial grain.... all the TDA parts ive seeen were monolithic outputs... (a single output device not a pair of ) and ill assume the same here... and all of them ive seen blew by them selves didnt take anything esle with it... so in all likelyhood simply replacing it will get you back up and running... the only caps associated with them are usually the supply filters and it would be unusuall to blow them up... but should be easy to tell as when these small one go they generall pop real good or at least ooze out material.... if you research that part # you mayfind a pin compatable higher wattage you could sub.... also some extra capacitence could give ya more deffinition in the bottom...
 
dragonworks said:
just put caps in that you are sure have as high or higher voltage and cap ratings as the existing ones an you should be ok. Actually, don't even replace them, bridge the ones that are there and see if it solves the problem.
Click to expand...

I don't think you'd want to do that. If the old caps are OK, then by paralleling new caps to them you will have doubled the capacitance, which will lower the rolloff point of the filter.
 
yeah, I think I'm gonna tentatively go with DC on this ..... is it blowing fuses the second you turn it on?
If so, I bet it's the output device ...... don't have a PN but find out what it is and try changing that. I don't have a strong opinion on the caps but if they're blown then they should show some physical evidence usually.
 
blown TDA7293

There is also a diode that shorts in the standby circuit. The reference # is
D19. The Marshall # is 6V8. I believe it is a 6volt zener diode. It is located on circuit board close to the power switch. It is behind REG3's heat sink.:D:D
 
Stratman1954 said:
There is also a diode that shorts in the standby circuit. The reference # is
D19. The Marshall # is 6V8. I believe it is a 6volt zener diode. It is located on circuit board close to the power switch. It is behind REG3's heat sink.:D:D
Click to expand...


I know this is an old thread, but I just have a MG250dfx with exactly the same problems to know:
- burned TDA7293v on both power amp channels
- D19 (6.8V zener diode) seems short (multimeter reads 2 ohms either direction)

I wonder if any of you guys were able to solve this and can share what the final solution is. I puchased new TDA7293 ICs and soldered into the power amp board and also replaced the D19 but before I turn things on, just wanted to make sure all that had to be replaced is node (do not want to burn another TDA :) ).

Many thanks!

JokeRz
 
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