Marshall MG100HDFX as a present with blown fuse!

[DS-1]

Hi guys!

I friend of mine gave me his old amp, a Marshall MG100HDFX head version and it told me that it was not working at all.

It came with a blown fuse. I started to find what could be wrong and I've found here: https://music-electronics-forum.com/...-tda7293/page3 that this amp has sometimes a faulty TDA7293.

So I've ordered the TDA and swapped other components, as read in the link:

TDA7293
d14 with a 6v8
d17 with a 1n414
tr2 with a 3904
c98 with a 220uF/50v.

The amp still blown fuse as I turn it on. If I disconnect the power amp board, it stay on without issues and the fan is spinning.

What else could I check?

Thanks in advance for the reply!

[The Dude]

I'd first check your power rails, since you already replaced the output device. If you are missing a rail, the amp will put out DC voltage likely causing a fuse to blow if a load is connected. Also, I wouldn't hook up a speaker until you verify that there is no DC on the output.

[DS-1]

I'd first check your power rails, since you already replaced the output device. If you are missing a rail, the amp will put out DC voltage likely causing a fuse to blow if a load is connected. Also, I wouldn't hook up a speaker until you verify that there is no DC on the output.

Can I do measurements with power amp board disconnected? Should I check for DC on the pins that goes from the main board to the power amp mini board?

[x-pro]

You can and should. Also, if the burnt parts have been removed from the power amplifier board, check the supply voltage on the board as well.

[DS-1]

You can and should. Also, if the burnt parts have been removed from the power amplifier board, check the supply voltage on the board as well.

I've replaced the old TDA with a new one and also I replaced all the other components listed in the first post. So now I have the new TDA installed on the small power amplifier board.

[The Dude]

Understood that you replaced the TDA. The questions is, are power rails to the IC there and correct voltage? The output IC will not work correctly if power to the IC is not correct.