Marshall MF350 Schematic and Specs

[xtian]

How can an unloaded power transformer pull 25 watts?

That does not sound like a healthy PT to me.

Agree. So, what are the two PT secondary windings supposed to be providing? The schematic (attached) is shy on voltage readings.

[xtian]

The PT is marked TXMA 00111, and says on the label that the secondaries are 19v and 32v, and I'm measuring 27.5v and 46.3v unloaded. This time, I removed the bulb limiter from the circuit, and I see that the PT draws only 12 watts by itself. So that was a false assumption that it was drawing 25 watts.

With the secondaries disconnected, it's easy to measure that the FWBR for the LT rails is burned. And this leads towards the power modules, so it's not a leap to presume one of the output power modules shorted.

[JamesJen]

I wish I would have done a little more research before I bought this amp. I got about 6 months out of it before it let me down. Amp 1 is less than half the volume of Amp 2,3 and 4.
It is pretty much unusable. Does that sound like a blown IC ?

[Jazz P Bass]

I wish I would have done a little more research before I bought this amp. I got about 6 months out of it before it let me down. Amp 1 is less than half the volume of Amp 2,3 and 4.
It is pretty much unusable. Does that sound like a blown IC ?

What do mean by "Amp 1,2 3 & 4"?
The preamp channels?

If you have any 'blown' Output ic's, the amp will not work at all.
It will blow the fuse.

[JamesJen]

Yes the preamp channels
on the head itself they are listed as amp 1 2 3 4
Amp 1 being the clean channel