Technics SA5760

[jakdedert]

Just got into this beast, a 165 wpc receiver from late 70's. Symptoms:
no power out to the speakers. When first put onto the bench, it worked,
but took a long time to kick out of protect, and one channel was
intermittantly noisy even with volume down...no significant DC on the
outputs.

Now, nothing...although signal present on tape outs.

I really could use a schematic for this monster, but poking around
reveals a couple of burned (but not open) resistors on the main board:
R-686 & R-687; both 22k 1/4 watt units, and both adjacent to R-708, a
270 ohm 5 watter which appears to get inordinantly hot. These parts
seem to be associated with TR-707, 701 & 702.

Like I said, I could really use a schematic for this relic, although if
someone is familiar with it, I could be 'walked through....' I recently
acquired it from the friend, to whom I sold it over 25 years ago when I
was a stereo dealer. It was blowing speakers, although from the telling
of the story, that appeared to be 'operator error'.

jak

 

[Jerry G.]

I cannot remember this set in detail, but I recall in many of these
sets changing the output devices, protection relay, and a fair amount
of caps. There were caps that were going high in ESR causing the set to
go in to protect, and also causing some device failures.

Jerry G.

 

[Ray L. Volts]

I really could use a schematic for this monster

http://www.manualman.com/catalog/news119.htm

$15.00

http://www.servicemanuals.net

$16 download; $17-$19 paper or fiche

 

[Mark D. Zacharias]

Watch out if you unplug the driver board! The molex connector is off by one
pin intentionally. If you plug it in the way it "looks" like it should go,
virtually every part on both amp channels will be fried. Been there, done
that. Later versions had a warning label along the top of the board. The
only clue is the small angle iron brace at the top doesn't line up correctly
unless the pins are offset by one.

Mark Z.

 

[jakdedert]

Watch out if you unplug the driver board! The molex connector is off by one
pin intentionally. If you plug it in the way it "looks" like it should go,
virtually every part on both amp channels will be fried. Been there, done
that. Later versions had a warning label along the top of the board. The
only clue is the small angle iron brace at the top doesn't line up correctly
unless the pins are offset by one.

YIKES!!!

I actually 'have' already pulled that board...no warning label either.
I did a test fit of the board with power off and unit unplugged. It
will indeed go in wrong if one is not careful--in fact 'looks' right.
The key, as you say, is to line up the holes on the hold down tabs; but
one can also look at the large molex...line up on that and ignore the
small one on the other end (which has one extra pin).

Thanks for the heads up. I really want to hear this one 'sing' again.

Mark Z.

Thanks, Ray. I know how to Google. I tried to order a download last
evening, but their system wouldn't accept my login or
registration...says someone with my email has already registered with a
different password. This is impossible for security reasons I won't go
into here (not impossible for someone else to have registered, just
impossible for it to have been me with a different password). I've
emailed them. I was hoping (not in vain, as you can see from the above)
that someone might have some personal experience with it.

Then there's the hope of not having to *spend* $16.......

jak

 

[jakdedert]

I cannot remember this set in detail, but I recall in many of these
sets changing the output devices, protection relay, and a fair amount
of caps. There were caps that were going high in ESR causing the set to
go in to protect, and also causing some device failures.

I was hoping it was a little less involved; but will go to a good deal
of trouble to get this one running. There are quite a few caps in
there, and I don't have an ESR meter. I believe the outputs are okay.
The relay could be an issue. Do you recall if it merely disco's the
speaker outs, or the B+/B- lines?

So far, in hopes of getting the schematic before doing detailed
t'shooting, I've only poked around, half at random. I did measure
voltages on the relay, and looked (in vain) for signal there. The only
significant voltage there was +/- 72v on two of the pins.

It does exhibit some symptoms of the protection circuit being the main
issue. As stated in the OP, there was no DC on the outputs when it was
working. AC voltage was even--channel to channel--and linear with
increasing input. I measured over 30v using only interstation FM noise
for a signal. I never got around to actually hooking up
speakers...instead used 100w dummy load, listened through the headphone
output. Both sides sounded clean except for the previously mentioned
intermittant crackling in the right channel.

Any other recollections of fixing this relic would be helpful...anyone?

jak

 

[mark]

If their's only crackling on one side and everything else sounds ok
through the output not out of the headphone jack it can be a noisy
transistor if you have a scope check the driver of that channel for noise. I
don't know the specific receiver but this is a general check for that type
of problem.

 

[Ray L. Volts]

Thanks, Ray. I know how to Google. I tried to order a download last

evening, but their system wouldn't accept my login or registration...says
someone with my email has already registered with a different password.
This is impossible for security reasons I won't go into here (not
impossible for someone else to have registered, just impossible for it to
have been me with a different password). I've emailed them. I was hoping
(not in vain, as you can see from the above) that someone might have some
personal experience with it.

Then there's the hope of not having to *spend* $16.......

It's also part of the SAMS MHF-118 book. I have 116 and 119, but somehow
missed 117 and 118! So close and yet so far...

 

[jakdedert]

If their's only crackling on one side and everything else sounds ok
through the output not out of the headphone jack it can be a noisy
transistor if you have a scope check the driver of that channel for noise. I
don't know the specific receiver but this is a general check for that type
of problem.

Missed the OP, I guess. It blew. No output of any kind now. Initially
it acted as detailed...then went completely out. The relay doesn't kick
in, but no overload (front LED) indicator lit.

Thanks for the response. I was looking for detailed info on that
particular model. I have a scope. When I finally get my shop moved and
set back up again, I'll trace the sig through from front to back and do
detailed t'shooting. I was hoping for a quick fix....<sigh>

jak

 

[jakdedert]

It's also part of the SAMS MHF-118 book. I have 116 and 119, but somehow
missed 117 and 118! So close and yet so far...

Thanks anyway. I got an answer, registered, and paid for the d/l. They
still need to scan it I guess, as it wasn't immediately available.

jak

 

[Mark D. Zacharias]

Missed the OP, I guess. It blew. No output of any kind now. Initially
it acted as detailed...then went completely out. The relay doesn't kick
in, but no overload (front LED) indicator lit.

Thanks for the response. I was looking for detailed info on that
particular model. I have a scope. When I finally get my shop moved and
set back up again, I'll trace the sig through from front to back and do
detailed t'shooting. I was hoping for a quick fix....<sigh>

jak

There was a voltage regulator transistor, a 2SD313 or some such, that would
go bad on these. It was on the tone board, as I recall, but quite
accessible. You can see it back in there behind the power switch, right
there on the long horizontal board which runs almost the length of the front
panel. It's on a small heat sink. Didn't mention it before because it didn't
relate to any crackling, but it would explain no sound, and the protect
relay not coming on.

Mark Z.

 

[jakdedert]

There was a voltage regulator transistor, a 2SD313 or some such, that would
go bad on these. It was on the tone board, as I recall, but quite
accessible. You can see it back in there behind the power switch, right
there on the long horizontal board which runs almost the length of the front
panel. It's on a small heat sink. Didn't mention it before because it didn't
relate to any crackling, but it would explain no sound, and the protect
relay not coming on.

Mark Z.

Thanks, Mark. I've just returned from a long weekend, and the Holidays
are at hand...but, I've gotten the manual and have begun tracing the
signal on paper. I'll stick some probes into it soon. I may have some
questions later. The PDF file doesn't show the voltages printed on the
circuit board traces very well, but....

jak

 

[Spark]

Technics SA-5760 information

I have a Technics SA-5760 that powers up, selector light indicates, but no audio. There is also dark(burnt) area in the middle of the main board. I'm in need of a schematic, parts list, actually any documentation would be greatly appreciated.