While waiting for some more TA7317P devices for my previous replair I was
handed a Yamaha XM6150 six channel power amplifier with the channel C
protection light on.

After removing the top cover I was curious what the four huge inductors were
for and wondered if I was dealing with a class D system. Some of the mystery
was cleared up by googling EEEngine:
http://www.yamahacommercialaudio.com...ine/index.html

I'm not sure I fully understand how it does what is claimed. I've never seen
anything like it before in an audio amplifier.

Next I obtained the service manual. There doesn't seem to be a direct link
but if you google yamaha_xm4220_xm6150.pdf the elektrotanya site will
provide it.

The power amp schematic is the one at the top of the last page with the
darlington output transistors.

I quickly found +55V on the orange wire to the relay board (CN806) and
further tests showed, unsurprisingly, that both darlington output
transistors (2SD2560 and 2SB1647) for that channel are short circuit.

Under a bright light I don't see any burned components or other damage. The
D2560 has obviously been very hot as it has toasted the board a little.

I'm thinking of trying a TIP122/127 pair to see if everything works properly
at low power before I blow up a new pair of correct devices.

Any other suggestions are welcome.

Old guy