John Smith wrote in message
...
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...30_power_ampli
fier/product_index/50_eeengine/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




I'm only familiar with Yamaha Stagepas 300
If your one is made with lightness in mind and 2 channel, check whether the
audio outputs are antiphase, ie one has "tip" contact to ground, and ground
contact is hot