MF350 Mode Four musings, thoughts, comments

[drewl]

So I just replaced all four blown TDA7293's.
Powered amp up without those boards connected and everything looks okay.
The caps and traces on the 4 output boards are good.

Before I reinstall the boards and test:
The heatsinks are hot, stay away from those.
No grounding of speaker output ground, otherwise it'll just blow up again.

The amp has a "load protection" circuit.....guess it doesn't work too well.

I was thinking of insulating the rear pins of the 7293's with shrink tubing to prevent possible arcing which may contribute to failures, but why bother.

[woodyc]

The several I've seen fail have been connected to a cab with a 4 ohm switch. At 4 Ohms, they sound great for about 10 minutes, then poof.

The whole output stage power issue is unfortunate because otherwise the amp is super loud and very versatile. It doesn't do everything but the clean rivals any pedal steel amp, and there is enough distortion for death metal.

[Steve Conner]

I've always fancied picking up a blown one of these cheap and replacing the whole power section with something more robust.

[Enzo]

Now THERE is some clear thinking.

[drewl]

I've read all the horror stories here but never had one in for blown outputs yet.
I've replaced 7293's and similiar output amp chips in many other amps, think I bought like 25 of them last time whatever one of the price breaks was, and I'm already down to just two.

Anyway, everything is working fine now, just needs some cleaning and maintenance.