Marshall MG100DFX repair advice please

[SH73]

I recently bought a second hand Marshall MG100DFX. The fan was a bit too loud so I cleaned it out. The fan and the cooling unit were dusty. For a good measure I sprayed a bit of switch cleaner in the fan and all the potentiometers. I plugged the amp in to test if the fan would be quite. I forgot to plug in the speaker. As I switched it on , there was a piping sound and a small flash next to the cooling unit. The amp doesn't work. The T1.6AL fuse on the pcb is blown. I read that replacing the fuse and trying again may cause further damage , so a bit reluctant to replace the fuse. Anyone can suggest what the issue may be or is it money down the drain? 

Edited February 21, 2022 by SH73
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[SH73]

Thinking whether I caused a short circuit with a switch cleaner and will be ok once dried out evaporated? The part that sparked is the yellow thing in second pic. It doesn't look discoloured.

Edited February 21, 2022 by SH73
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[Dad3353]

2 hours ago, SH73 said:

Thinking whether I caused a short circuit with a switch cleaner and will be ok once dried out evaporated?...

 

That board is the power amp; the active part that churns out the 100w is that multi-legged black thing at the bottom, under the heat sink. If the fuse has blown, with a spark or flash, it's very likely shot. It will do no further harm to replace the fuse with one of exactly the same rating; it will in all likelihood blow too. In that case, the amp is dead, but it may be possible to obtain a new power module, which is easy to replace (Plug'n'Play...). The power IC itself (the black thing...) costs about a fiver (TDA7293V...), but may blow again if there's other faults on that board. If you can't do this yourself, take it to a Good, Reliable Repair Man and get an estimate. It's not a hard fix for someone competent.
Hope this helps. 

[SH73]

1 hour ago, Dad3353 said:

 

That board is the power amp; the active part that churns out the 100w is that multi-legged black thing at the bottom, under the heat sink. If the fuse has blown, with a spark or flash, it's very likely shot. It will do no further harm to replace the fuse with one of exactly the same rating; it will in all likelihood blow too. In that case, the amp is dead, but it may be possible to obtain a new power module, which is easy to replace (Plug'n'Play...). The power IC itself (the black thing...) costs about a fiver (TDA7293V...), but may blow again if there's other faults on that board. If you can't do this yourself, take it to a Good, Reliable Repair Man and get an estimate. It's not a hard fix for someone competent.
Hope this helps. 

Thanks, I've been pretty much watching You Tube videos this afternoon on replacing TDA93V or the whole power module. They're suggesting the same as you. The only thing I can't see is any discoloration of the soldering joint suggesting that the IC has had it. I try the fuse first, then the whole power module. 

The only confusion is that the spark was from underneath the yellow capacitor 100 nj63. I ordered 20 fuses so I have a "play" tomorrow. I had the amp less than a week 😁

[SH73]

If anyone reads this thread, where are the places to get spare electronic parts, capacitors, PCB etc. E bay takes a long time...thanks

[John Cribbin]

Try Mouser or Farnell, personally eBay works for me.

[SH73]

Two faults I may or likely have done are.

1. After cleaning the fan , I didn't assemble the heatsink and fan using the screws that keep them isolated from the chassis, hence the spark...

2. The speaker wasn't connect to amp, it should have had a load no lower than 8 ohms.

 

Still waiting for fuses to re test, now everything connected as it should so fingers cross.

 

[SH73]

2 hours ago, John Cribbin said:

Try Mouser or Farnell, personally eBay works for me.

I already checked , Mouser out of stock Darnell , with delivery the price is nearly 3x higher. Ebay

[BassBunny]

1 hour ago, SH73 said:

The speaker wasn't connect to amp, it should have had a load no lower than 8 ohms.

Not connecting the speaker shouldn't have caused any problems as it's a solid state amp and they are usually quite happy without a load.

If it was a valve amp, that's a different story.

The "no lower than 8 Ohms" is the lowest impedance of a speaker when you do connect it.

[SH73]

So... The fuse arrived, installed the new fuse recording the board with phone so I can trace the potential spark ...Well. The amp works and is loud as flip. The fan is quiet now after I cleaned it. Thanks all who advised. @Dad3353. lesson learnt.." don't meddle with things you don't understand" ..

[rmorris]

23 hours ago, SH73 said:

If anyone reads this thread, where are the places to get spare electronic parts, capacitors, PCB etc. E bay takes a long time...thanks

 

CPC (part of Farnell but prices often cheaper with free delivery over £17 I think atm).

Ebay sellers can be quick if UK stock.