check the output tansistors for a shorted junction ... the big ones on the
heatsink , using a meter on the diode scale , check the 3 pins in any order
and if the meter zeros out then you have found it but also you need to check
the drivers in that section as well as sometimes those get trashed at the
same time ... good luck !



wrote in message
oups.com...
Greeting All,

Sony STR-DB930 receiver goes into protect mode. No earlier symptoms,
no prior intermittants.

I picked up the Sony factory service manual for this unit and, while it
contains good schematics, little is offered in terms of troubleshooting
info for diagnosing the "protect" fault.

1. I read about the grounding issue and while I found this doubtful
I'll give that ago later today not expecting a quick fix for this
issue.

2. When in protect mode, what is the nominal voltage reading that
should be on the external speaker connection points? (I suspect zero
since the relay controlling the outuputs would be zero).

3. What should be the voltage reading be on the input to the speaker
output relay?

4. The Protect circuit appears to monitor voltage and also seems to be
connected to current measuring circuits on each output channel. It
seems to look at a number of potential problems but then offers little
in the way of a back trace to root cause. If anyone could offer a few
starting points to assist me in diagnosing the fault that would be
great.

Regards,
re5513