[franco]

I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

Thanks in advance,

-Franco

[Eeyore]

franco wrote:

I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

No, the headphones will normally be run from the 'power stage'.


Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

It's not difficult in principle. Do you have experience troubleshooting
other electronics aside from audio ?

Posted to sci.electronics repair in addition.

Graham

[JANA]

How I service this type of fault is to put an audio generator on the
input. I usually use 1 kHz tone set to about 250 mv. I then take a scope
and follow through to see what stage is making the distortion. I then
take voltage readings and do the necessary tests to find the defective
parts.

There are a fair number of stages and many things in your receiver that
can cause a defect in the sound. It will take some experience, and most
likely the service manual will be required to find the faulty parts.

--

JANA
_____


"franco" wrote in message
...
I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

Thanks in advance,

-Franco

[franco]

On Jun 14, 11:45*pm, Eeyore
wrote:
franco wrote:
I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

No, the headphones will normally be run from the 'power stage'.
not the preamp stage?


Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

It's not difficult in principle. Do you have experience troubleshooting
other electronics aside from audio ?
some guitar tube amplifier stuff (very simple compared to this); my
friend helping me has experience in TVs and microwave ovens.


Posted to sci.electronics repair in addition.
Thank you.


Graham

[Eeyore]

franco wrote:

Eeyore wrote:
franco wrote:
I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

No, the headphones will normally be run from the 'power stage'.
not the preamp stage?

Not usually.


Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

It's not difficult in principle. Do you have experience troubleshooting
other electronics aside from audio ?
some guitar tube amplifier stuff (very simple compared to this); my
friend helping me has experience in TVs and microwave ovens.

Ok, well an perienced tech would know roughly where to probe without a
detailed schematic but it looks like you'll need one of those at minimum.
Model number ?

Graham

[isw]

In article ,
Eeyore wrote:

franco wrote:

Eeyore wrote:
franco wrote:
I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

No, the headphones will normally be run from the 'power stage'.
not the preamp stage?

Not usually.


Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

It's not difficult in principle. Do you have experience troubleshooting
other electronics aside from audio ?
some guitar tube amplifier stuff (very simple compared to this); my
friend helping me has experience in TVs and microwave ovens.

Ok, well an perienced tech would know roughly where to probe without a
detailed schematic but it looks like you'll need one of those at minimum.

You have a perfectly functioning amp right there (the other channel);
why not just compare and contrast? It's even a good source for parts to
swap...

Isaac

[Mark D. Zacharias[_2_]]

"franco" wrote in message
...
I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

Thanks in advance,

-Franco

You can try manipulating various controls and switches and see if any of
them affect your problem.

Probably not much else you can do without a schematic or at least some
experience actually troubleshooting electronic circuits.

Troubleshooting something like this, even with another functioning channel
nearby, is simply something you cannot hope to do without some basic
understanding of electronic circuits, types of parts, the failures they may
be prone to, and some experience.

There's lots of things that can cause distortion. Bad capacitors, resistors,
transistors, solder connections, etc.

Rotsa Ruck. No disrespect, but your chances of fixing this yourself or even
with the help of your friend, are just about nil.


Mark Z.

[Dave]

"franco" wrote in message
...
I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);
at all volumes (eliminating things before the volume knob);
with the headphones (eliminating the power stage?).

Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.

Thanks in advance,

-Franco

Yes, and I'd like to debug Windows Vista, but without some basic
understanding of computer operating systems it'd be a long long project...

Solid state amplifiers have been around for a long time, and the principles
are well-known. Poke around on the internet and do some reading on theory,
THEN start your repair.

As I've noted before, the "guess 'n check" or "shotgun" method of component
replacement makes for a frustrating, expensive, and time-consuming repair
process.

Dave

[Chris Hornbeck]

On Sat, 14 Jun 2008 19:15:59 -0700 (PDT), franco
wrote:

I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);

at all volumes (eliminating things before the volume knob);

I'm not certain how this was determined, but it's not bullet-proof.

with the headphones (eliminating the power stage?).

As others have said, not bullet-proof.


Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.


You have two channels, one working, one defective. How can you compare
them?

Do you have an oscilloscope? Is there a free software that performs
rudimentary scope functions with a soundcard?

If so, what you want to make is a "curve tracer". This is a way to
plot, real time, current vs. voltage. In operation, you stick its two
probes *anywhere* in a circuit, POWER OFF!, observe whether or not
it's the same as the other channel, make a mental note, and move on to
the next two locations.

As a beginner you'll need to start brute-force, comparing and often
removing components and comparing again to confirm that the difference
observed "in circuit" is truely that device, and not something
external but connected there.

Does that make sense?


If you're really interested, post back about what's available to you
to use as a scope. Trust me; anything else is misery. And this is
quite do-able, as a learning project, and more importantly, as a
confidence builder. You can do this. I'll help all, and possibly more
than, you want.

All the best fortune,

[jakdedert]

Chris Hornbeck wrote:
On Sat, 14 Jun 2008 19:15:59 -0700 (PDT), franco
wrote:

I have a Korean made Sherwood receiver circa 1980 that distorts on the
right channel only:
with all inputs (eliminating the sources);
with any set of speakers (not the speakers);

at all volumes (eliminating things before the volume knob);

I'm not certain how this was determined, but it's not bullet-proof.

with the headphones (eliminating the power stage?).

As others have said, not bullet-proof.


Does anyone have any advice troubleshooting this? I'm comfortable
replacing electronic components in circuit boards (when I say me I
mean my electronic savvy friend who is helping me out, He just
replaced leaky looking 1000u cap, but it didn't solve the problem) but
have no experience with stereo troubleshooting and would like to
attempt to fix this myself.


You have two channels, one working, one defective. How can you compare
them?

Do you have an oscilloscope? Is there a free software that performs
rudimentary scope functions with a soundcard?

If so, what you want to make is a "curve tracer". This is a way to
plot, real time, current vs. voltage. In operation, you stick its two
probes *anywhere* in a circuit, POWER OFF!, observe whether or not
it's the same as the other channel, make a mental note, and move on to
the next two locations.

As a beginner you'll need to start brute-force, comparing and often
removing components and comparing again to confirm that the difference
observed "in circuit" is truely that device, and not something
external but connected there.

Does that make sense?


If you're really interested, post back about what's available to you
to use as a scope. Trust me; anything else is misery. And this is
quite do-able, as a learning project, and more importantly, as a
confidence builder. You can do this. I'll help all, and possibly more
than, you want.

All the best fortune,

Much can be done with a cheap multimeter, if the scope is not available.
In fact, much of my audio dx is done mostly with it.

A signal tracer is also valuable. One can be made easily with a single
computer speaker and suitable probes, which can be simple as attaching
wire with an alligator clip to the ring of the 3.5mm stereo plug,
attaching that to the signal ground of the unit (the sleeve of any RCA
jack) and using the tip of the plug as a crude probe (make sure you use
the LEFT speaker, or short the tip to ring)...although something longer
and sharper would be superior. Better yet would be to cut off the plug
completely and solder on more conventional test probes.

Tracing the signal from the input (any input) of the preamp through the
switching (it was usually mechanical back then), then through the
various tone and driver stages could very well narrow down the section
to which the OP need look for the fault. When the clean signal
disappears and becomes distorted, you're in the right ballpark. Testing
various components can then be accomplished with the multimeter.

My money is on a dried out electrolytic cap, or a bad output device; but
it could be as simple as 28 year old dirt in one of those mechanical
controls.

Finally, this sort of thing is more appropriate to the ng
sci.electronics.repair, than to this group.

jak

[Chris Hornbeck]

On Mon, 16 Jun 2008 22:36:41 -0500, jakdedert
wrote:


Much can be done with a cheap multimeter, if the scope is not available.
In fact, much of my audio dx is done mostly with it.

A signal tracer is also valuable. One can be made easily with a single
computer speaker and suitable probes, which can be simple as attaching
wire with an alligator clip to the ring of the 3.5mm stereo plug,
attaching that to the signal ground of the unit (the sleeve of any RCA
jack) and using the tip of the plug as a crude probe (make sure you use
the LEFT speaker, or short the tip to ring)...although something longer
and sharper would be superior. Better yet would be to cut off the plug
completely and solder on more conventional test probes.

Tracing the signal from the input (any input) of the preamp through the
switching (it was usually mechanical back then), then through the
various tone and driver stages could very well narrow down the section
to which the OP need look for the fault. When the clean signal
disappears and becomes distorted, you're in the right ballpark. Testing
various components can then be accomplished with the multimeter.

My money is on a dried out electrolytic cap, or a bad output device; but
it could be as simple as 28 year old dirt in one of those mechanical
controls.

Possibly, but the usual case, when the headphone output is OK, is
that the output stage has failed. These tend to be fairly crappy at
best, because cost-sensitive, and hard-working, so comparatively
failure-prone.

Maybe we could agree that any serious repair would include the
cleaning of all switches and controls as a first and most important
step, and that essentially *all* of the electrolytic capacitors in
something 28 years old are bad or next thing to it.


A "repair", especially one that's non-professional, and a learning
experience on a piece of crap, could generously be defined as
replacing just enough to make it work. Anyway, that's the
framework I was thinking. Y'all might very easily and rightly
feel differently.

Maybe the OP will refine his (and it's always a safe bet on the
tech-geek Newsgroups that it's a "his" - bummer, but that's the
cards as dealt) interest level.


Much thanks, as always,

[jakdedert]

Chris Hornbeck wrote:
snip
My money is on a dried out electrolytic cap, or a bad output device; but
it could be as simple as 28 year old dirt in one of those mechanical
controls.

Possibly, but the usual case, when the headphone output is OK, is
that the output stage has failed. These tend to be fairly crappy at
best, because cost-sensitive, and hard-working, so comparatively
failure-prone.

Yeah, that's where I would start, actually...injecting some sort of sig
at the output (if chip amp) or testing the output devices (if
discrete)...although I'd have it hooked up to the scope as a matter of
course, displaying a sine wave, and attached to a dummy load.

If the OP is serious, he'll follow through and report some results to
help narrow it down.

Maybe we could agree that any serious repair would include the
cleaning of all switches and controls as a first and most important
step, and that essentially *all* of the electrolytic capacitors in
something 28 years old are bad or next thing to it.

It depends. If the unit has been sitting for some significant portion
of that 28 years, maybe most of the caps are suspect, but I've got ones
that have been sitting in my junk box for longer than that...and still
exhibit good ESR readings. If the unit has been in constant--or even
regular--use, IME they're not so prone to blanket failure.

A "repair", especially one that's non-professional, and a learning
experience on a piece of crap, could generously be defined as
replacing just enough to make it work. Anyway, that's the
framework I was thinking. Y'all might very easily and rightly
feel differently.

Depends on the application, but for the OP, getting it working will
probably suffice.

Maybe the OP will refine his (and it's always a safe bet on the
tech-geek Newsgroups that it's a "his" - bummer, but that's the
cards as dealt) interest level.

Yeah, I don't know too many females who regularly pick up a soldering iron.

Much thanks, as always,

Always,

jak

[[email protected]]

You are a likely to get any help from the "techs" here as you are to get
a CJ sound from your box.