Greetings.
I wonder if anyone has some insight into this problem.

This receiver uses two STK0177 power amplifier "blocks", each with 10
in-line connectors. The LH channel is highly distorted, the RH channel
is perfect. The distortion is present on FM, AM and AUX (with sig,
gen. input) so it's not the FM demodulator - it's definitely in the
audio stages.

The DC voltages on each of the two STK0177's power amplifier pins are
as follows (with 115 VAC supply):

Pin # RH channel LH channel (volts)
1 +0.251 +0.229
2 +0.002 +0.002
3 +0.255 +0.229
4 -26.90 -26.77
5 -1.272 -1.288
6 -28.29 -28.28
7 +0.060 +0.20
8 +28.23 +28.22
9 +1.309 +1.257
0 +26.95 +26.77

(I hope the columns hold together!)

I have not yet put a 'scope on each STK0177 line to watch for clipping
or drive distortion (pin-out not known.) Nothing gets too hot and
there is no perceptible difference in temperature between the two heat
sinks (but they are thermally connected do some degree, so that's not
conclusive.).

Do people think this is a failed STK0177? Or is there another
candidate component? Unfortunately, I do not have the schematic.
Also, does anyone have a pointer or URL to the pinout and/or spec
sheet for the STK0177? I did a quick Google but with no success.

BTW, this unit is very difficult to service since all the electronics
are on one large PCB and you can't access the bottom of this PCB
without disconnecting just about everything and lifting it up (unlike
other Technics models where you can take out the metal floor plate.)

Thanks for all comments.

Cheers,

Roger

I'm not at all sure the voltages are far enough off to suggest a problem
with an output IC. Have you just tried manipulating the various controls and
switches to eliminate them first?

If you swap the output IC's, that would be the final test.

That's an odd STK number though, you might have trouble finding one. I use
East Coast Transistor parts for old STK's - they can usually suggest a good
sub number if one exists.


Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.


"Engineer" wrote in message
...
Greetings.
I wonder if anyone has some insight into this problem.

This receiver uses two STK0177 power amplifier "blocks", each with 10
in-line connectors. The LH channel is highly distorted, the RH channel
is perfect. The distortion is present on FM, AM and AUX (with sig,
gen. input) so it's not the FM demodulator - it's definitely in the
audio stages.

The DC voltages on each of the two STK0177's power amplifier pins are
as follows (with 115 VAC supply):

Pin # RH channel LH channel (volts)
1 +0.251 +0.229
2 +0.002 +0.002
3 +0.255 +0.229
4 -26.90 -26.77
5 -1.272 -1.288
6 -28.29 -28.28
7 +0.060 +0.20
8 +28.23 +28.22
9 +1.309 +1.257
0 +26.95 +26.77

(I hope the columns hold together!)

I have not yet put a 'scope on each STK0177 line to watch for clipping
or drive distortion (pin-out not known.) Nothing gets too hot and
there is no perceptible difference in temperature between the two heat
sinks (but they are thermally connected do some degree, so that's not
conclusive.).

Do people think this is a failed STK0177? Or is there another
candidate component? Unfortunately, I do not have the schematic.
Also, does anyone have a pointer or URL to the pinout and/or spec
sheet for the STK0177? I did a quick Google but with no success.

BTW, this unit is very difficult to service since all the electronics
are on one large PCB and you can't access the bottom of this PCB
without disconnecting just about everything and lifting it up (unlike
other Technics models where you can take out the metal floor plate.)

Thanks for all comments.

Cheers,

Roger

"Engineer" bravely wrote to "All" (16 Jun 04 23:04:54)
--- on the heady topic of "Technics SA5160 distortion on one channel"

En From: "Engineer"

En Greetings.
En I wonder if anyone has some insight into this problem.

En This receiver uses two STK0177 power amplifier "blocks", each with 10
En in-line connectors. The LH channel is highly distorted, the RH channel
En is perfect. The distortion is present on FM, AM and AUX (with sig,
En gen. input) so it's not the FM demodulator - it's definitely in the
En audio stages.

En The DC voltages on each of the two STK0177's power amplifier pins are
En as follows (with 115 VAC supply):

En Pin # RH channel LH channel (volts)
En 1 +0.251 +0.229
En 2 +0.002 +0.002
En 3 +0.255 +0.229
En 4 -26.90 -26.77
En 5 -1.272 -1.288
En 6 -28.29 -28.28
En 7 +0.060 +0.20
En 8 +28.23 +28.22
En 9 +1.309 +1.257
En 0 +26.95 +26.77

En (I hope the columns hold together!)

En I have not yet put a 'scope on each STK0177 line to watch for clipping
En or drive distortion (pin-out not known.) Nothing gets too hot and
En there is no perceptible difference in temperature between the two heat
En sinks (but they are thermally connected do some degree, so that's not
En conclusive.).

En Do people think this is a failed STK0177? Or is there another
En candidate component? Unfortunately, I do not have the schematic.
En Also, does anyone have a pointer or URL to the pinout and/or spec
En sheet for the STK0177? I did a quick Google but with no success.

En BTW, this unit is very difficult to service since all the electronics
En are on one large PCB and you can't access the bottom of this PCB
En without disconnecting just about everything and lifting it up (unlike
En other Technics models where you can take out the metal floor plate.)

En Thanks for all comments.

En Cheers,

En Roger

With a lot of obvious distortion a scope will just confirm it but it
could be useful to locate where it starts. If Pin 7 is the output to
the speakers then 0.20 volts on the left channel is certainly cause
enough for distortion. The +Vcc is also a little low compared to -Vcc.
This unbalance indicates the IC is sourcing significant current from
the positive supply into the speaker. Try and measure the same voltage
without the speakers. If it goes way up then the IC could be bad.
However, a leaky coupling cap can also unbalance the IC or high ESR
can cause a parasitic oscillation though the latter isn't as likely.
Good luck and be careful!

A*s*i*m*o*v

.... KPLA: Klingon Radio: All Klingon Opera, All The Time.

See below...

"Mark D. Zacharias" wrote in message
...
I'm not at all sure the voltages are far enough off to suggest a
problem
with an output IC. Have you just tried manipulating the various
controls and
switches to eliminate them first?

Yes, all OK.

If you swap the output IC's, that would be the final test.

Good point! But that is a VERY difficult job on this board (see below
in my text.) I may have to do it, though.

That's an odd STK number though, you might have trouble finding one.
I use
East Coast Transistor parts for old STK's - they can usually suggest
a good
sub number if one exists.

Thanks for that idea - will file it for future use.

Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and
spam
have rendered my regular e-mail address useless.


"Engineer" wrote in message
...
Greetings.
I wonder if anyone has some insight into this problem.

This receiver uses two STK0177 power amplifier "blocks", each with
10
in-line connectors. The LH channel is highly distorted, the RH
channel
is perfect. The distortion is present on FM, AM and AUX (with
sig,
gen. input) so it's not the FM demodulator - it's definitely in
the
audio stages.

The DC voltages on each of the two STK0177's power amplifier pins
are
as follows (with 115 VAC supply):

Pin # RH channel LH channel (volts)
1 +0.251 +0.229
2 +0.002 +0.002
3 +0.255 +0.229
4 -26.90 -26.77
5 -1.272 -1.288
6 -28.29 -28.28
7 +0.060 +0.20
8 +28.23 +28.22
9 +1.309 +1.257
0 +26.95 +26.77

(I hope the columns hold together!)

I have not yet put a 'scope on each STK0177 line to watch for
clipping
or drive distortion (pin-out not known.) Nothing gets too hot and
there is no perceptible difference in temperature between the two
heat
sinks (but they are thermally connected do some degree, so that's
not
conclusive.).

Do people think this is a failed STK0177? Or is there another
candidate component? Unfortunately, I do not have the schematic.
Also, does anyone have a pointer or URL to the pinout and/or spec
sheet for the STK0177? I did a quick Google but with no success.

BTW, this unit is very difficult to service since all the
electronics
are on one large PCB and you can't access the bottom of this PCB
without disconnecting just about everything and lifting it up
(unlike
other Technics models where you can take out the metal floor
plate.)

Thanks for all comments.

Cheers,

Roger

See below...

"Asimov" wrote in
message ...
"Engineer" bravely wrote to "All" (16 Jun 04 23:04:54)
--- on the heady topic of "Technics SA5160 distortion on one
channel"

En From: "Engineer"

En Greetings.
En I wonder if anyone has some insight into this problem.

(snip)

With a lot of obvious distortion a scope will just confirm it but it
could be useful to locate where it starts.

That was my plan.

If Pin 7 is the output to
the speakers then 0.20 volts on the left channel is certainly cause
enough for distortion.

Damn, that's a typo! It's actually 0.020 VDC, a bit less than the RH
channel.
I don't know the pin-out but I plan to measure the voltage across the
speaker termimals with and w/o a speaker connected, RH and LH
channels.

The +Vcc is also a little low compared to -Vcc.
This unbalance indicates the IC is sourcing significant current from
the positive supply into the speaker. Try and measure the same
voltage
without the speakers. If it goes way up then the IC could be bad.
However, a leaky coupling cap can also unbalance the IC or high ESR
can cause a parasitic oscillation though the latter isn't as likely.
Good luck and be careful!

Thanks.


A*s*i*m*o*v

... KPLA: Klingon Radio: All Klingon Opera, All The Time.

Cheers,

Roger

"Engineer" wrote in message
...
Greetings.
I wonder if anyone has some insight into this problem.

(snip)

Pin # RH channel LH channel (volts)
1 +0.251 +0.229
2 +0.002 +0.002
3 +0.255 +0.229
4 -26.90 -26.77
5 -1.272 -1.288
6 -28.29 -28.28
7 +0.060 +0.20 Typo! It's 0.020 VDC
8 +28.23 +28.22
9 +1.309 +1.257
0 +26.95 +26.77

(snip)

Cheers,

Roger

you can get the ic's from WES COMPONENTS
phone - 0297979866
or email
thay are listed for $24.75

john!

"Engineer" wrote in message
...
Greetings.
I wonder if anyone has some insight into this problem.

This receiver uses two STK0177 power amplifier "blocks", each with 10
in-line connectors. The LH channel is highly distorted, the RH channel
is perfect. The distortion is present on FM, AM and AUX (with sig,
gen. input) so it's not the FM demodulator - it's definitely in the
audio stages.

The DC voltages on each of the two STK0177's power amplifier pins are
as follows (with 115 VAC supply):

Pin # RH channel LH channel (volts)
1 +0.251 +0.229
2 +0.002 +0.002
3 +0.255 +0.229
4 -26.90 -26.77
5 -1.272 -1.288
6 -28.29 -28.28
7 +0.060 +0.20
8 +28.23 +28.22
9 +1.309 +1.257
0 +26.95 +26.77

(I hope the columns hold together!)

I have not yet put a 'scope on each STK0177 line to watch for clipping
or drive distortion (pin-out not known.) Nothing gets too hot and
there is no perceptible difference in temperature between the two heat
sinks (but they are thermally connected do some degree, so that's not
conclusive.).

Do people think this is a failed STK0177? Or is there another
candidate component? Unfortunately, I do not have the schematic.
Also, does anyone have a pointer or URL to the pinout and/or spec
sheet for the STK0177? I did a quick Google but with no success.

BTW, this unit is very difficult to service since all the electronics
are on one large PCB and you can't access the bottom of this PCB
without disconnecting just about everything and lifting it up (unlike
other Technics models where you can take out the metal floor plate.)

Thanks for all comments.

Cheers,

Roger