MG100 HDFX no power HELP!!

[Tonyrenhae]

Ok, so I bought a used MG100 HDFX and 4 * 12 angled cab. it was all working fine apart from the fan being a little loud. I decided to replace the fan with a standard PC 50mm fan and that all worked fine. Now here's where I get stupid...
Wanting to see how much noise the new fan was making, I tried to stop it by jamming a pair of pliers to stop the fan turning. unfortunately, this resulted in a large amount of sparks being produced from the little heat sink thingy behind the fan, as well as a loud noise being emitted before everything went quiet. Now, the amp refuses to turn on at all. I don't think the fuse is broken and have tried a new fuse with no luck, and am really hoping this is a simple fix.

Many thanks in advance.

[Fragger]

Man I hate it when I do that... I`ve learned to jam nonconducting things into amps; plastic silverware, wooden chopsticks, q-tip, etc.
~~
Here`s a video of a fan being replaced and what the fan and heat sink looks like if anyone is curious (like me).
Marshall MG100HDFX Amp Fan Fix Tutorial - YouTube

[g1]

If there were sparks you must have shorted the heatsink to the chassis. This most likely will have blown the power amp IC's.

[Fragger]

More good info in this thread Tonyrenhae:
Marshall MG100HDFX - TD7293

[Enzo]

Don't assume the fuses are OK, pull each one and test it with an ohm meter.

[Jazz P Bass]

Those little plastic thingies on the fan screws?

They are there to isolate the heatsink from chassis ground.

The heatsink, being attached to the rear plane of the TDA7293 output ic, and not having a mica isolater, is at the -Vdc level of the power supply.

Shorting the -Vdc to ground should not have damaged the output IC.

Replace the fuse, you may be good to go.

NOTE: the lack of the mica between the TDA7293 & the heatsink is for better heat conduction.
Putting a mica in between is not advisable.

[soundguruman]

You blew up the power amp.
The FAN is the INSULATOR. That's why it's a special fan. It has special threaded inserts...to insulate the heatsink from the chassis.
The heat sink is energized. (you found this, the hard way)

Check replace the zener diode, D14, 6.8 volt 1/2 watt.
Replace the power amp module. (usually)
I have them in stock if you need one.
MArshall_MG100DFX.pdf

[Enzo]

Grounding the tab shorts the power supply to ground. That shouldn't damage the power amp module.