Marshall MG100HFDX

[tube dude]

HI Folks,
Here is the problem I am having with this MG100: blows fuses.
I disconnected the 2 red wires of the transformer and amp does come on.
Once I re connected the 2 red wires..well fuse blows.
Could it be the transformer, caps or the chip mounted on the heat sink?
How do you test a tranny? How do you know that the chip may be the problem.
I really have some bad feelings about this amp. Very cheaply made and seems very
fragile.....
Hope someone can figure this out.
Any help would be greatly appreciated.
Take care all and don't get shocked!!!
Tube Dude

[52 Bill]

HI Folks,
Here is the problem I am having with this MG100: blows fuses.
I disconnected the 2 red wires of the transformer and amp does come on.
Once I re connected the 2 red wires..well fuse blows.

Welcome to the place. We've discussed these amps a lot around here. If you search the forum you'll find a number of posts.

If you pulled the red transformer leads and the amp powers up, it pretty much means that the transformer is ok.

The usual problems are that the output chips die for any number of reasons. Try pulling off the connector that connects the output chips to the main board. If it powers up without blowing the fuse, then you've found your problem. If the chip is dead you can either replace just the chip or you can buy the entire board.

If you have a light bulb limiter, you can save your fuses until you get things sorted out.

[Enzo]

If one of your power ICs has failed, replace them both. Seriously.

Mouser sells the TDA7293 IC reasonably.

[tube dude]

Hi Folks,
I mistakenly sent my question about this MG100 HDFX to Enzo, I thought it went in the forum under Other Amps.
To Enzo, I apologize.
I did locate the problem. The previous owner had messed around with the fan/heat sink of the 7293 and one of the
mounting screw was not straight in the mount and well there you are, causing it to short to the chassis. Of course the
chip blew! I replaced it and it rocks out now!
Enzo thanks for the help.
If any of you work on these little creatures be sure to mount it correctly, keeping the nylon eye spacers in the hole. I took my meter and tested for continuity
from the screw heads to chassis. You can also check from the mounting screw to the cooling plate of the 7293. It will act like a diode and beep once and that's okay. If it continues there a short!!! yada yada yada!
Good luck to you all.
Tube Dude

[Jazz P Bass]

Oh yeah.
The TDA backplane is connected to the B- rail.
Hense the nylon isolators.
What a goofy setup.