wrote in message
ups.com...
I've got an Integra DTR-5 (nearly identical to the Onkyo TX-DS 575)
thats in circuit protection mode (immediately goes into standby as soon
as the the power switch is pressed on, and opens the main power relay).
There is nothing connected to the receiver. Jammy Harbin's reply on a
identical subject back on 8/20/04 stated "DC bias on the output,
Shorted finals...". With it disconnected from power, I ohm'ed the
speaker terminals - all the black neg terminals are about .2-.4 ohms,
and the red pos terminals are infinite. What exactly do I check, and
how do I check it? Can DC bias be checked while in circuit protection
mode? I don't see any popped capacitors, burnt chips, or cracked
traces, but I should probably get a brighter light. Can the output amps
be checked in circuit?

I've got the service manual and schematics (I can scan and post
specific schematics if necessary), and am comfortable with following
electronics kits, but am new at troubleshooting. If I remove the fuse
which connects the main transformer and then power on, it stays out of
circuit protection (the main power relay stays closed). Thanks for any
help!

Andris

The most likely scenario is that it is detecting a DC offset on one of the
channels, but if you are new to faultfinding, you will probably struggle to
get to the bottom of the problem with any certainty that you can confidently
switch back on, without finishing up with another pile of dead components.
The reason that you read infinity on the speaker lives, is because these are
connected to the output stages via the output relay(s), which will be
remaining open, if the unit is in protect.

To check for DC offset, you need to measure at the output transistors'
midpoint, which will be at the junction of the two low value emitter
resistors (assuming that the amp uses conventional output devices, and not
an STK hybrid). At idle, you should have zero volts, or very very close to
zero, on this point. If you find any offset on any channel, then it's likely
that one or other or both of the output transistors has failed, but that is
unlikely to be the end of the story. With a DC coupled amp, the problem can
be coming from virtually anywhere right back to the front end, and other
transistors besides the outputs, will likely be faulty. If it does use an
STK hybrid - and I seem to recall that Onkyos don't - then any DC offset
will normally be cured, without any other issues, by simply replacing it. If
you don't detect any offset, then the problem is with the protect circuit
itself (not unusual), but sometimes, these monitor many parameters, and can
be an absolute bitch to troubleshoot.

If you have a full-rail offset on all channels - say +45v - then look for a
missing negative rail or vice versa.

I don't mean to put you off, but honestly, if you are new to faultfinding,
this kind of project is not something I would recommend to a beginner. Most
of us who are involved in repairing this kind of gear daily, bypass the
power switching, and use a variac to bring up the supply slowly, so that we
can measure what's going on (wrong !!) before all those shiny new
transistors fail again ... Good luck with it.

Arfa