Unlike another reply here, don't replace the outputs unless they are
shorted, which they are not. Replace the STK350-230. Common problem. There
may be another issue with the protect circuit if it's not protecting when it
should.

Mark Z.


"Perion" wrote in message
...
If anyone is REAL bored maybe you could print this out, have a look at the
schematic at (pdf) at
http://mywebpages.comcast.net/dharp/.../STR_DE515.pdf . It's
the
closest I can find to my str-se501 - the amplifier section is real close
to what
I have. See page 2 - at about G21. [All 5 of my ch. amps are like the top
three - I don't have IC601 or IC651]

Here's the deal:
1. It goes into protect mode - duh....

2. All the speaker relays for each channel are energized.

3. Center channel is reading full supply voltage (sum of B+ and B- vs.
just B+
or B- like all the other channels) on each of its output transistors from
collector to base! The other channels have near zero vdc on the base and
B+ or
B- from base to collector. Getting B+ to the base of Q553 and B- to the
base of
Q554). Also, output xistor resistances different than other four channels.

4. Removed both center ch transistors. Still goes into protect mode.
Traced
where opposite supply voltages on the bases back to STL350-230 center
channel
driver IC. The other 4 channels all read the same and have identical
static ckt.
resistances - they are driven from uPC2581 driver ICs. Probably explains
why
center ch. reading different resistances than other four.

5. Removed the STK350-230 center ch. driver IC. No more weird voltage
readings
at the output xistors' solder points. On the STK350-230 IC I was getting
B+ on
pin 6 (+VEOUT) to the base of the Q553 and B- on pin 5 (-VEOUT) to the
base of
the Q554 which seems crap to me - maybe I'm wrong. Anyway, it still goes
into
protect mode.

6. Can't find anything else that doesn't seem right on any of the
channels.

Question:
1. Any brilliant insights into this?
2. If it goes into protect mode, shouldn't at least one of the channel's
amp
over load detect transistors (like Q570) be turned on and inhibit that
amp's
associated speaker relay?
3. Down at R6 (the signals to the display board) it seems to get its
"protect
in" signal (24) from the "OC Offset DET" (overcurrent detector?) at D25.
It
looks to me like this monitors each channel's over load detectors so
again, if
in protect mode, shouldn't at least one channel's overload detector be
turned?
4. Do I have to do something special to reset protect mode other than
power down
and back up?

thanks,
Perion