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Tracing into my Sony STR-501

P

Perion

Jan 1, 1970
0
Hi

My Sony home theater str-501 is in protect mode due to internal overload. The
center channel output transistor pair reads different (ohming the junctions in
circuit) than the other four channels - all channels use the same PNP-NPN pair
type. I also noticed that after going into protect, the center channel pair
transistors had 120 vdc across two leads (one's the emitter - not sure of the
other - probably collector - haven't looked up the pinout yet) while all the
other pairs had +60 for one xistor and -60 for the same leads. I popped out the
center ch. pair - still goes into protect mode. The center ch. outputs are
driven from an stx350-??? IC - the other channels are driven from two uPC????
driver chips [don't have the numbers at the moment]. I popped out the stx350-???
but still goes into protect mode. I can't find any bad transistors (using static
diode check on Fluke), shorted caps, etc. Any ideas or does anyone have any
deeper details of typical Sony's amps?

Also, there are some tiny "biasing transistors" also pasted to the main heat
sink. What are these for and could they cause the problem? Haven't checked them
yet - wasn't time last night.

Thanks,
Perion
 
J

Jerry G.

Jan 1, 1970
0
Since all these are DC coupled, it is very important to check all the
biasing and drive transistors as well. It is also important to check for
any caps that are low in ESR, or that have become resistive. If you had
a shorted output transistor, also check for any opened bias resistors.

--

Jerry G.
======

Hi

My Sony home theater str-501 is in protect mode due to internal
overload. The
center channel output transistor pair reads different (ohming the
junctions in
circuit) than the other four channels - all channels use the same
PNP-NPN pair
type. I also noticed that after going into protect, the center channel
pair
transistors had 120 vdc across two leads (one's the emitter - not sure
of the
other - probably collector - haven't looked up the pinout yet) while all
the
other pairs had +60 for one xistor and -60 for the same leads. I popped
out the
center ch. pair - still goes into protect mode. The center ch. outputs
are
driven from an stx350-??? IC - the other channels are driven from two
uPC????
driver chips [don't have the numbers at the moment]. I popped out the
stx350-???
but still goes into protect mode. I can't find any bad transistors
(using static
diode check on Fluke), shorted caps, etc. Any ideas or does anyone have
any
deeper details of typical Sony's amps?

Also, there are some tiny "biasing transistors" also pasted to the main
heat
sink. What are these for and could they cause the problem? Haven't
checked them
yet - wasn't time last night.

Thanks,
Perion
 
J

JVC Dude

Jan 1, 1970
0
The centre pins on the outputs are normally the Collector.
Some units have enough monitoring that they won't run with many parts
disconnected.
The collectors on the outputs should have +60 or -60 on them depending on
which they are.
the emitters (right pin) should have 0v on them. I'd confirm the 2 outputs
are faulty then replace just them first.
The thermal transistors are only for shutting down/limiting the amp from
running away with itself when hot. They rarely fail

AW
 
P

Perion

Jan 1, 1970
0
JVC Dude said:
The centre pins on the outputs are normally the Collector.
Some units have enough monitoring that they won't run with many parts
disconnected.
The collectors on the outputs should have +60 or -60 on them depending on
which they are.
the emitters (right pin) should have 0v on them. I'd confirm the 2 outputs
are faulty then replace just them first.
The thermal transistors are only for shutting down/limiting the amp from
running away with itself when hot. They rarely fail
I found the schematics for a model with nearly identical output circuit parts,
layout, and component designation. I uploaded it to
http://mywebpages.comcast.net/dharp/files/str_se501/STR-DE335_SE391_V323.pdf.

I'll check it out tonight at work and see what the deal is. Probably post a more
detailed question tonight.
BTW - the center channel circuit is in the lower left corner on page 6 in the
pdf schematic - Q603 and Q604. I had 120 vdc on each of them instead instead of
60 (like B+ and B- instead of B+ and 0v and B- to 0v).

Perion
 
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