Yamaha Blown Amp help nearly solved -see schematic -

[Wdyorchid]

During a heavy right speaker load the amp blows taking the speaker down with
it. A service technician confirms a blown amp but unable to diagnose further
without a schematic. So here it is.

http://autotails.tripod.com/yamaha.htm

Follow the orange line in this schematic and as you approach Q105 the problem
begins. This sorta predriver and everything after it measures off its normal
reading by 5,000%. It's remarkable that the output (main) transistor isn't
dead since I'd had it tested outside and even put new ones in it's place and
still measure 5,000% of normal.

The problem began when the speaker output measured:
Left channel 28V
Right channel 28V
Center channel 0V
Surround channel 0V
The system will shut down after two seconds, cannot bypass

See this link for the areas marked in green (similar to above schematic) are
the blown areas. Everything else around it measures normal. Also will find more
diagnostic details,
http://autotails.tripod.com/zoom.htm
Website maintained by a coworker.

Receiver is a Dolby pro logic RX-V480 70w/channel x3 channel plus two op-amp
surround channels with a separate power supply.

 

[Wdyorchid]

Q111 was replaced this morning, still won't work. Q111 was replaced the same
time as Q109, Q129C, and Q129A. Measuremwnts were taken and I was shocked to
see that the were still the same as before. (Thinking Q111, Q109 drives the
output transistors (Q129A, Q129C, replacing them would solve something) Thanks
for the suggestions.
-W

I suspect at least Q111 to be defective. If the voltage difference
between B-E is much higher > 0.7 it is. Good chance that Q129A
is also shorted between B-E so it is perhaps better to
replace all of them.

During a heavy right speaker load the amp blows taking the speaker down
with
it. A service technician confirms a blown amp but unable to diagnose
further
without a schematic. So here it is.

http://autotails.tripod.com/yamaha.htm

Follow the orange line in this schematic and as you approach Q105 the
problem
begins. This sorta predriver and everything after it measures off its
normal
reading by 5,000%. It's remarkable that the output (main) transistor
isn't
dead since I'd had it tested outside and even put new ones in it's place
and
still measure 5,000% of normal.

The problem began when the speaker output measured:
Left channel 28V
Right channel 28V
Center channel 0V
Surround channel 0V
The system will shut down after two seconds, cannot bypass

See this link for the areas marked in green (similar to above schematic)
are
the blown areas. Everything else around it measures normal. Also will find
more
diagnostic details,
http://autotails.tripod.com/zoom.htm
Website maintained by a coworker.

Receiver is a Dolby pro logic RX-V480 70w/channel x3 channel plus two
op-amp
surround channels with a separate power supply.