Pioneer SX-780 Problem

[Gary K.]

I have a Pioneer SX-780 AM/FM Stereo Receiver/AMP. Recently, I was
using it to power the speakers from the TV source, and went to bed and
forgot to shut off the unit (while the door to the entertainment center
was closed). Next morning, the unit no longer worked. If you turn on
the power switch, lighting comes on but the 5 second delay circuit no
longer "clicks" on. Consequently, nothing from the AM/FM tuner or any
other sources or output.

Could the unit have built up enough heat overnight while on with the
source disabled (TV was shut off)? Any ideas as to what damage was
caused and possible remedy? There seems to be a fuse assembly on the
schematic, but since the lights work as do the switched and unswitched
outlet, I would think that was not the issue.

Thanks.

Sent via Deja.com http://www.deja.com/
Before you buy.

[Mike Suhm]

I just finished repairing an Aiwa mini-system with the identical problem.
Everything appeared to work, but the delay circuit was not engaging and no
sound at all. I had to replace the main output IC. That was all.

Mike / Audio Pros
audi...@execpc.com

"Gary K." <gkami...@my-deja.com> wrote in message
news:90339p$sr7$1...@nnrp1.deja.com...

[Gary K.]

In article <3a255291$0$54341$272e...@news.execpc.com>,

"Mike Suhm" <audi...@execpc.com> wrote:
> I just finished repairing an Aiwa mini-system with the identical
problem.
> Everything appeared to work, but the delay circuit was not engaging
and no
> sound at all. I had to replace the main output IC. That was all.
>
> Mike / Audio Pros
> audi...@execpc.com
>

Thanks, Mike. Hopefully that's all there is to the problem. Course I
should think that if the entire Amp was shot the unit would exhibit the
same symptoms, i.e., there would be nothing to delay to.

[TIM SCHWARTZ]

Gary,
Most likely one of the STK-0050 output IC's has failed. The 'delay'
circuit is actually a protection circuit, which will prevent DC from
getting to your speakers in case of amplifier failure. It is also
possible that other things have failed. There are 3 voltage regulator
transistors that often need resoldering in these units.

Regards,
Tim Schwartz
Bristol Electronics

Gary K. wrote:
>
> I have a Pioneer SX-780 AM/FM Stereo Receiver/AMP. Recently, I was
> using it to power the speakers from the TV source, and went to bed and
> forgot to shut off the unit (while the door to the entertainment center
> was closed). Next morning, the unit no longer worked. If you turn on
> the power switch, lighting comes on but the 5 second delay circuit no
> longer "clicks" on. Consequently, nothing from the AM/FM tuner or any
> other sources or output.
>
> Could the unit have built up enough heat overnight while on with the
> source disabled (TV was shut off)? Any ideas as to what damage was
> caused and possible remedy? There seems to be a fuse assembly on the
> schematic, but since the lights work as do the switched and unswitched
> outlet, I would think that was not the issue.
>
> Thanks.
>

[Gary K.]

In article <3A263E...@worldnet.att.net>,

TIM SCHWARTZ <tosch...@worldnet.att.net> wrote:
> Gary,
> Most likely one of the STK-0050 output IC's has failed.
The 'delay'
> circuit is actually a protection circuit, which will prevent DC from
> getting to your speakers in case of amplifier failure. It is also
> possible that other things have failed. There are 3 voltage regulator
> transistors that often need resoldering in these units.
>
> Regards,
> Tim Schwartz
> Bristol Electronics
>

Thanks Tim. Entertain me and tell me roughly how much this would cost
to repair if as you guess.

[TIM SCHWARTZ]

FYI, I'd expect most shops to charge around $50-75 labor, and $15-35 for
the IC. The STK-0050 has been discontinued, and can be difficult to
find. (last time I had to use a STK-0060, which requires drilling new
mounting holes in the heatsink) I'd expect that to include cleaning
switches and controls as needed, touching up the soldering on the
voltage regulators, and a quick touch-up of the FM front end. I WOULD
NOT expect a total FM alignment, lamps, or other problems to be
included. If its worth putting $75-110 into this receiver is a
judgement call.

[Gary K.]

In article <3A279A...@worldnet.att.net>,

Thanks Tim for the honest assessment. You've probably saved me some
time and money, unit unseen. Just curious, what should I do with the
unit if I don't repair it? Simply discard it, or is there any need for
these?

[Alan Maier]

Gary,

Before you toss out the Pioneer SX-780, do keep in mind that there is a
market for used late 1970s -early 1980s era equipment. There are always
nuts like me to buy them on eBay, painstakingly restore them, and give them
a new lease on life as a hobby.

You can find a used (working) SX-780 for less than the repair cost.... but
don't waste your money on a current model. Even your hybrid chip equipped
SX-780 is very solid compared to what you buy new today. IMHO Pioneers SX
_50 series was far more solid than the SX-_80 series. A SX-750 is a quite a
bit more receiver, as example.

BTW Tim, if you are reading this... I put that SX-580 aside for a while -
quite a puzzle! It's not the muting circuit as thought.

Alan

"Gary K." <gkami...@my-deja.com> wrote in message

news:908d7p$7cv$1...@nnrp1.deja.com...
: In article <3A279A...@worldnet.att.net>,

[Gary K.]

In article <3A263E...@worldnet.att.net>,
TIM SCHWARTZ <tosch...@worldnet.att.net> wrote:
> Gary,
> Most likely one of the STK-0050 output IC's has failed.
The 'delay'
> circuit is actually a protection circuit, which will prevent DC from
> getting to your speakers in case of amplifier failure. It is also
> possible that other things have failed. There are 3 voltage regulator
> transistors that often need resoldering in these units.
>
> Regards,
> Tim Schwartz
> Bristol Electronics
>

> Gary K. wrote:
> >
> > I have a Pioneer SX-780 AM/FM Stereo Receiver/AMP. Recently, I was
> > using it to power the speakers from the TV source, and went to bed
and
> > forgot to shut off the unit (while the door to the entertainment
center
> > was closed). Next morning, the unit no longer worked. If you turn
on
> > the power switch, lighting comes on but the 5 second delay circuit
no
> > longer "clicks" on. Consequently, nothing from the AM/FM tuner or
any
> > other sources or output.
> >
> > Could the unit have built up enough heat overnight while on with the
> > source disabled (TV was shut off)? Any ideas as to what damage was
> > caused and possible remedy? There seems to be a fuse assembly on
the
> > schematic, but since the lights work as do the switched and
unswitched
> > outlet, I would think that was not the issue.
> >
> > Thanks.
> >

> > Sent via Deja.com http://www.deja.com/
> > Before you buy.
>

Any chance I could be lucky and one of the 4 fuses could be gone? I
can't see a break in any of them but maybe I should swap them out just
in case?

[TIM SCHWARTZ]

Gary,
I usually check them with an ohm meter, but they are certainly cheap
enough, and it couldn't hurt. How was the soldering on the regulators?

Regards,
Tim

[ABL Electronic Service]

Another possibilty is the power supply regulators. If the AM, FM AUX
indicators are not on that is likely the case.

Larry

On Sun, 03 Dec 2000 13:18:46 GMT, TIM SCHWARTZ
<tosch...@worldnet.att.net> wrote: