Hello,

I'm trying to service this unit (I have three units with the same problem)
and the -B supply for the pre-drivers starts out at -59 (+59 is ok) and then
right before the spk relay closes the voltage drops to -31 volts.

I did trace it to the overload protect circuit. The schematic states it's
the -B switch. One of the pre drivers gets very warm. The unit does not go
into protect mode.

The outputs check out. At this point, I don't know if it is the 7v line or
if it is one of the pre drivers pulling it down after a few seconds.

Any ideas?

Thanks

They do this on purpose to trigger the protection circuit.

It's a "feature", not a defect..

You will find that if you feed a sine wave to 2 (or was it 3?) channels
simultaneously via the 5.1 inputs, you can run to full power into 8 ohms
with no problem. Add one more channel, and it will consistently go into
protect WAY before it gets full power on all channels. I suspect this is to
get away with a bit smaller power transformer.

If you read between the lines in the power specs, you'll see that the full
power specs aren't given with all channels running simultaneously.

I already chased this one myself.

Mark .Z


wrote in message ...
Hello,

I'm trying to service this unit (I have three units with the same problem)
and the -B supply for the pre-drivers starts out at -59 (+59 is ok) and
then
right before the spk relay closes the voltage drops to -31 volts.

I did trace it to the overload protect circuit. The schematic states it's
the -B switch. One of the pre drivers gets very warm. The unit does not go
into protect mode.

The outputs check out. At this point, I don't know if it is the 7v line or
if it is one of the pre drivers pulling it down after a few seconds.

Any ideas?

Thanks

Hello again,

The +60 and -60 volts to the outputs is correct. It does not change. The
volume is at min and no input signal.

The 30v zener that is on the collector of Q692 (BN2F4M) should be 6.3 volts
but it's -31 volts(it seems it starts out about 4.5 to 5v then goes to
-31v).
The emitter of the same transistor starts out at about 4.5v and then
goes down to about 3.5v. According to the Service Manual it should be 6.3v.
The base should be -5.8v but it is -3.5v.
The other voltages on the pre-driver pins seems to jive with the SM specs.

I did trace the 7v back to the 7v regulator. The output of the reg. drops to
3 to 4 volts. The 15v going to the input on the reg stays around 17v.

I am not sure if it's the overload detect amp and Q691, 692 or the 7v line
that has the problem or if it is the upc2581's that have a problem.

Would I be able to desolder all of the outputs and remove the upc2581 pre
drivers and then try to power it on.

Do you think it would destroy anything? I have desoldered outputs before,
but not the pre drivers with out problems.

Note: If I disconnect the Surround Back board from the main board the -59 is
-31v almost instantly at power on.
With it connect to the main board, you get a about 3 sec before the voltage
drops from -59v to 31v.

I know on other STR-DE units I have repaired, the voltage did not drop.

Thanks for your help!
Jimmy

The voltage drops on the one rail to the drivers, not the outputs. If you
remove the 2581 driver(s) you'll just get no DC drive to the outputs, hence
no sound, no bias, no nothing.

Mark Z.


wrote in message ...
Hello again,

The +60 and -60 volts to the outputs is correct. It does not change. The
volume is at min and no input signal.

The 30v zener that is on the collector of Q692 (BN2F4M) should be 6.3
volts
but it's -31 volts(it seems it starts out about 4.5 to 5v then goes to
-31v).
The emitter of the same transistor starts out at about 4.5v and then
goes down to about 3.5v. According to the Service Manual it should be
6.3v.
The base should be -5.8v but it is -3.5v.
The other voltages on the pre-driver pins seems to jive with the SM specs.

I did trace the 7v back to the 7v regulator. The output of the reg. drops
to
3 to 4 volts. The 15v going to the input on the reg stays around 17v.

I am not sure if it's the overload detect amp and Q691, 692 or the 7v line
that has the problem or if it is the upc2581's that have a problem.

Would I be able to desolder all of the outputs and remove the upc2581 pre
drivers and then try to power it on.

Do you think it would destroy anything? I have desoldered outputs before,
but not the pre drivers with out problems.

Note: If I disconnect the Surround Back board from the main board the -59
is
-31v almost instantly at power on.
With it connect to the main board, you get a about 3 sec before the
voltage
drops from -59v to 31v.

I know on other STR-DE units I have repaired, the voltage did not drop.

Thanks for your help!
Jimmy