Technics SA-310 Intermittent Weak Left Channel

[William R. Walsh]

Hello all...

I thought that I'd clean the badly pitted contacts on the protection relay
in my Technics SA-560 receiver and got a little carried away. Turns out I
broke some of the fine turns of magnet wire on the coil while I was trying
to open the relay's case. So while I wait for my replacement relay, I pulled
a little SA-310 out of storage.

The SA-310 basically works fine, but I've noticed that if I turn up the
volume up high, the left channel starts to become weak and distorted.
Turning the volume back down restores perfect sound. The controls are clean.
I'm thinking it's a power supply problem, maybe weak filter caps not being
able to keep up with the increased power demands. It dates from 1983, so
maybe it's due for some maintenance...

Any thoughts on this? Am I on the right track?

William

 

[William R. Walsh]

Hi!

Measure the B+ at the output stage on the suspect channel as you apply a
1khz sine wave from min to max output and report back.

I don't have any way of doing that. Any other ideas for a test that would
produce a similar result?

William

 

[Meat Plow]

On Sun, 15 Aug 2010 18:14:29 -0500, William R. Walsh wrote:

Hello all...

I thought that I'd clean the badly pitted contacts on the protection
relay in my Technics SA-560 receiver and got a little carried away.
Turns out I broke some of the fine turns of magnet wire on the coil
while I was trying to open the relay's case. So while I wait for my
replacement relay, I pulled a little SA-310 out of storage.

The SA-310 basically works fine, but I've noticed that if I turn up the
volume up high, the left channel starts to become weak and distorted.
Turning the volume back down restores perfect sound. The controls are
clean. I'm thinking it's a power supply problem, maybe weak filter caps
not being able to keep up with the increased power demands. It dates
from 1983, so maybe it's due for some maintenance...

Any thoughts on this? Am I on the right track?

William

Measure the B+ at the output stage on the suspect channel as you apply a
1khz sine wave from min to max output and report back.



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Mark Zacharias]

"William R. Walsh" <newsgroups1@idontwantjunqueemail.walshcomptech.com>
wrote in message news:Tb-dnXWkarbnCfXRnZ2dnUVZ_qSdnZ2d@mchsi.com...

Hi!

Measure the B+ at the output stage on the suspect channel as you apply a
1khz sine wave from min to max output and report back.

I don't have any way of doing that. Any other ideas for a test that would
produce a similar result?

William

Could be dirty controls, but it really sounds like maybe a bad output IC to
me. Do try pushing turning wiggling etc the various controls and switches
and see if any of them affect your problem. Maybe not much else you can do.

Mark Z.

 

[Meat Plow]

On Sun, 15 Aug 2010 20:29:55 -0500, William R. Walsh wrote:

Hi!

Measure the B+ at the output stage on the suspect channel as you apply
a 1khz sine wave from min to max output and report back.

I don't have any way of doing that. Any other ideas for a test that
would produce a similar result?

William

None I can think of other than using an alternative audio source like an
FM tuner or tape playback to generate signal and monitor the rail
voltages with an analog meter or digital with a logarithmic display.
If it falls more than say 10% at full volume you may have an issue with
the rail supply. That's about it, can't help more if you don't have a
minimal amount of test gear like an audio generator and volt meter.





--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Arfa Daily]

"Mark Zacharias" <mark_zacharias@sbcglobal.net> wrote in message
news:4c691e79$0$14508$c3e8da3@news.astraweb.com...

"William R. Walsh" <newsgroups1@idontwantjunqueemail.walshcomptech.com
wrote in message news:Tb-dnXWkarbnCfXRnZ2dnUVZ_qSdnZ2d@mchsi.com...
Hi!

Measure the B+ at the output stage on the suspect channel as you apply a
1khz sine wave from min to max output and report back.

I don't have any way of doing that. Any other ideas for a test that would
produce a similar result?

William


Could be dirty controls, but it really sounds like maybe a bad output IC
to me. Do try pushing turning wiggling etc the various controls and
switches and see if any of them affect your problem. Maybe not much else
you can do.

Mark Z.

As Mark says, but I would also feel inclined to check the soldering on the
output devices, as Pans and Technics are buggers for bad joints on any
heatsink-attached devices, on virtually any models.

Arfa

 

[William R. Walsh]

Hi!

As Mark says, but I would also feel inclined to check the soldering on the
output devices, as Pans and Technics are buggers for bad joints on any
heatsink-attached devices, on virtually any models.

I did try playing through all the sources and they're all equally affected.
Output from the Tape REC connection is clean and undistorted. The controls
on the unit are clean and in good shape, push buttons and sliders alike.

I've noticed bad soldering in these units. I was in the SA-560 at first to
fix the nonworking indicator LEDs in the front panel. What little solder
there was on the ones that didn't work just vaporized when I touched it. My
SA-929 had bad soldering on its protection relay coil connections. I also
have a Technics equalizer where many of the indicator lights above the
pushbuttons didn't work...and it was the same thing.

So I'll take a look. It would be nice to get the unit running like it should
again, and I would hope that I don't have to replace the STK2038 II module.
There's a replacement on eBay but it's listed as a "generic" part and I'm
not sure how I feel about that. I would have reservations about its quality
or ability to meet specifications.

William

 

[William R. Walsh]

Hi!

None I can think of other than using an alternative audio source like an
FM tuner or tape playback to generate signal and monitor the rail
voltages with an analog meter or digital with a logarithmic display.
If it falls more than say 10% at full volume you may have an issue with
the rail supply. That's about it, can't help more if you don't have a
minimal amount of test gear like an audio generator and volt meter.

I do have an analog multimeter (if I can find it!) that would probably do.
What I don't have is any sort of an audio signal generator. It did occur to
me that I have some various audio frequency sweeps and the like stored on my
computer, but I don't know if there are any fixed frequency samples in
there.

My intention is to perform some checks on the power supply. I did notice
what looked like dimming or blanking from the tuning display during loud
passages in the music. It was so brief that I could not be sure.

William

 

[William R. Walsh]

Hi!

Personally I haven't seen a lot of standard pass-filtered
supplies dip in voltage drastically enough to weaken the output of the
channel significantly and intermittently as in your case. I'd be looking
for a lose connection first.

Eventually the left channel "stuck" in its broken state. Now it's distorted
no matter the volume or source. I've also noticed a "thump" sound from the
left speaker at startup where there was none before. (The right channel
continues to function normally.) Knowing these receivers' tendency to put a
power supply rail on a speaker without warning, I've taken the good speakers
away and put crappy ones in their place.

About an hour ago, I powered the unit up and played the drums on it to see
if anything was obviously loose. That failed to produce a result, so I took
Arfa's advice and examined the soldering on the STK 2038 II module. I found
only two joints that looked suspect, so I redid them and found no
improvement in the units' behavior. I looked all over the main board and
didn't find any other problems.

I suspect the power supply--especially the filter caps--mainly because this
unit runs *very* hot and always has. It'll get hot enough that you don't
want to keep your hand on the top of the cover. The filter capacitors sit in
the worst of this heat, right between the power transformer and power
amplifier module. What kind of shape could those and other capacitors in the
vicinity be after 27 years? They're 85 degree C units, so I wonder...and
replacements are cheap enough...

William

 

[Meat Plow]

On Mon, 16 Aug 2010 11:56:51 -0500, William R. Walsh wrote:

Hi!

None I can think of other than using an alternative audio source like
an FM tuner or tape playback to generate signal and monitor the rail
voltages with an analog meter or digital with a logarithmic display. If
it falls more than say 10% at full volume you may have an issue with
the rail supply. That's about it, can't help more if you don't have a
minimal amount of test gear like an audio generator and volt meter.

I do have an analog multimeter (if I can find it!) that would probably
do. What I don't have is any sort of an audio signal generator. It did
occur to me that I have some various audio frequency sweeps and the like
stored on my computer, but I don't know if there are any fixed frequency
samples in there.

My intention is to perform some checks on the power supply. I did notice
what looked like dimming or blanking from the tuning display during loud
passages in the music. It was so brief that I could not be sure.

William

Basically you want to put a load on the power supply. Any way you can get
the volume up so you can observe the drop, if any, in voltage on the rail
could help you. Personally I haven't seen a lot of standard pass-filtered
supplies dip in voltage drastically enough to weaken the output of the
channel significantly and intermittently as in your case. I'd be looking
for a lose connection first.



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Meat Plow]

On Mon, 16 Aug 2010 13:48:44 -0500, William R. Walsh wrote:

Hi!

Personally I haven't seen a lot of standard pass-filtered supplies dip
in voltage drastically enough to weaken the output of the channel
significantly and intermittently as in your case. I'd be looking for a
lose connection first.

Eventually the left channel "stuck" in its broken state. Now it's
distorted no matter the volume or source. I've also noticed a "thump"
sound from the left speaker at startup where there was none before. (The
right channel continues to function normally.) Knowing these receivers'
tendency to put a power supply rail on a speaker without warning, I've
taken the good speakers away and put crappy ones in their place.

About an hour ago, I powered the unit up and played the drums on it to
see if anything was obviously loose. That failed to produce a result, so
I took Arfa's advice and examined the soldering on the STK 2038 II
module. I found only two joints that looked suspect, so I redid them and
found no improvement in the units' behavior. I looked all over the main
board and didn't find any other problems.

I suspect the power supply--especially the filter caps--mainly because
this unit runs *very* hot and always has. It'll get hot enough that you
don't want to keep your hand on the top of the cover. The filter
capacitors sit in the worst of this heat, right between the power
transformer and power amplifier module. What kind of shape could those
and other capacitors in the vicinity be after 27 years? They're 85
degree C units, so I wonder...and replacements are cheap enough...

William

You could always swap the caps since each channel has its own pair. Or
just shotgun them all and cross your fingers.



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Arfa Daily]

"William R. Walsh" <newsgroups1@idontwantjunqueemail.walshcomptech.com>
wrote in message news:ZbqdnWGcB-688fTRnZ2dnUVZ_q2dnZ2d@mchsi.com...

Hi!

As Mark says, but I would also feel inclined to check the soldering on
the
output devices, as Pans and Technics are buggers for bad joints on any
heatsink-attached devices, on virtually any models.

I did try playing through all the sources and they're all equally
affected.
Output from the Tape REC connection is clean and undistorted. The controls
on the unit are clean and in good shape, push buttons and sliders alike.

I've noticed bad soldering in these units. I was in the SA-560 at first to
fix the nonworking indicator LEDs in the front panel. What little solder
there was on the ones that didn't work just vaporized when I touched it.
My
SA-929 had bad soldering on its protection relay coil connections. I also
have a Technics equalizer where many of the indicator lights above the
pushbuttons didn't work...and it was the same thing.

So I'll take a look. It would be nice to get the unit running like it
should
again, and I would hope that I don't have to replace the STK2038 II
module.
There's a replacement on eBay but it's listed as a "generic" part and I'm
not sure how I feel about that. I would have reservations about its
quality
or ability to meet specifications.

William

I reckon about a 70% chance that you will find several 'cracked right round'
joints on that STK, which may or may not be the source of your current
problem, but which will need attending to anyway ...

Arfa

 

[Arfa Daily]

"William R. Walsh" <newsgroups1@idontwantjunqueemail.walshcomptech.com>
wrote in message news:4pWdnS6RcN1N8PTRnZ2dnUVZ_judnZ2d@mchsi.com...

Hi!

None I can think of other than using an alternative audio source like an
FM tuner or tape playback to generate signal and monitor the rail
voltages with an analog meter or digital with a logarithmic display.
If it falls more than say 10% at full volume you may have an issue with
the rail supply. That's about it, can't help more if you don't have a
minimal amount of test gear like an audio generator and volt meter.

I do have an analog multimeter (if I can find it!) that would probably do.
What I don't have is any sort of an audio signal generator. It did occur
to
me that I have some various audio frequency sweeps and the like stored on
my
computer, but I don't know if there are any fixed frequency samples in
there.

My intention is to perform some checks on the power supply. I did notice
what looked like dimming or blanking from the tuning display during loud
passages in the music. It was so brief that I could not be sure.

William

Do you have any kind of iPod Touch or iPhone ? There are a number of rather
good free signal generator apps available. I have a couple on my Touch.

Arfa

 

[Mark Zacharias]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:epkao.20214$Dt3.13835@hurricane...

"William R. Walsh" <newsgroups1@idontwantjunqueemail.walshcomptech.com
wrote in message news:ZbqdnWGcB-688fTRnZ2dnUVZ_q2dnZ2d@mchsi.com...
Hi!

As Mark says, but I would also feel inclined to check the soldering on
the
output devices, as Pans and Technics are buggers for bad joints on any
heatsink-attached devices, on virtually any models.

I did try playing through all the sources and they're all equally
affected.
Output from the Tape REC connection is clean and undistorted. The
controls
on the unit are clean and in good shape, push buttons and sliders alike.

I've noticed bad soldering in these units. I was in the SA-560 at first
to
fix the nonworking indicator LEDs in the front panel. What little solder
there was on the ones that didn't work just vaporized when I touched it.
My
SA-929 had bad soldering on its protection relay coil connections. I also
have a Technics equalizer where many of the indicator lights above the
pushbuttons didn't work...and it was the same thing.

So I'll take a look. It would be nice to get the unit running like it
should
again, and I would hope that I don't have to replace the STK2038 II
module.
There's a replacement on eBay but it's listed as a "generic" part and I'm
not sure how I feel about that. I would have reservations about its
quality
or ability to meet specifications.

William



I reckon about a 70% chance that you will find several 'cracked right
round' joints on that STK, which may or may not be the source of your
current problem, but which will need attending to anyway ...

Arfa

The ones I've seen with the notoriously bad solder connections are much
later models using the SVI series outputs - not STK.

Mark Z.

 

[William R. Walsh]

Hi!

You could always swap the caps since each channel has its own
pair. Or just shotgun them all and cross your fingers.

I swapped the caps at the kitchen table and held my breath. There was no
improvement in the unit's behavior at all.

Thinking that I'd rather not smell burnt speaker coils, I put a speaker
protection device between the receiver and the crappy speakers. All of a
sudden, the protection device kicked in and muted the left channel. I
haven't checked to be sure, but my guess is that the hybrid module's left
channel finally went completely bad. (At the moment, I can't find my
multimeter.) Interestingly, the headphone output still seems to be OK. I'm
not sure where its signal comes from.

I found some replacement modules on eBay and ordered two of them. They're
said to be generic replacements, so I hope they come close to meeting the
specifications of the original. I also intend to find a suitable power
source in the unit for a small fan that I will mount to the heatsink. And I
sure won't crank it up that high ever again!

Replacing the amplifier module doesn't seem to be so bad (16 pins) but I am
wondering about what work might be required to finish the job. Would there
be any need for bias or other adjustments? I have the service manual but it
does not mention anything about this. Only removing the module and its
heatsink are discussed.

William

 

[William R. Walsh]

Hi!

Do you have any kind of iPod Touch or iPhone?

Yes, I have a first generation iPod Touch. I should have thought of
that..."there's an app for that" too I guess.

Out of the applications you have, is there any one that stands out above the
rest, whether free or not?

William

 

[William R. Walsh]

Hi!

The ones I've seen with the notoriously bad solder connections are much
later models using the SVI series outputs - not STK.

The solder on this unit looked bombproof. I could only find one joint--and
this was only if I squinted at it the right way--that looked bad in any way.
So I redid it, made it look "perfect" and found no improvement. I guess I'll
get to practice sixteen times when my new module arrives.

I've found plenty of other bad solder connections (but I think I mentioned
that already)...some of the panel indicators on my SA-560 and an equalizer
of some kind (don't recall the model #) needed to be redone before they'd
work. The EQ was easy, the SA-560 not so much.

Was there any difference to speak of between an STK and the SVI modules? The
"SVI" designation struck me as nothing more than a house numbering scheme
from Matsushita Electric, and some of my service manuals show an SVI
numbered part when the actual receiver had an STK-XXXX II of some type in
it. I also saw similar numbering with the tuning microcontroller...SVIxxxxx
in the book, and the actual part number/manufacturer name in the receiver.

William

 

[Meat Plow]

On Wed, 18 Aug 2010 19:59:37 -0500, William R. Walsh wrote:

Hi!

You could always swap the caps since each channel has its own pair. Or
just shotgun them all and cross your fingers.

I swapped the caps at the kitchen table and held my breath. There was no
improvement in the unit's behavior at all.

Thinking that I'd rather not smell burnt speaker coils, I put a speaker
protection device between the receiver and the crappy speakers. All of a
sudden, the protection device kicked in and muted the left channel. I
haven't checked to be sure, but my guess is that the hybrid module's
left channel finally went completely bad. (At the moment, I can't find
my multimeter.) Interestingly, the headphone output still seems to be
OK. I'm not sure where its signal comes from.

I found some replacement modules on eBay and ordered two of them.
They're said to be generic replacements, so I hope they come close to
meeting the specifications of the original. I also intend to find a
suitable power source in the unit for a small fan that I will mount to
the heatsink. And I sure won't crank it up that high ever again!

Replacing the amplifier module doesn't seem to be so bad (16 pins) but I
am wondering about what work might be required to finish the job. Would
there be any need for bias or other adjustments? I have the service
manual but it does not mention anything about this. Only removing the
module and its heatsink are discussed.

William

I don't think you need to worry about biasing a hybrid module. Those
things are STK-something right?



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Meat Plow]

On Wed, 18 Aug 2010 20:00:45 -0500, William R. Walsh wrote:

Hi!

Do you have any kind of iPod Touch or iPhone?

Yes, I have a first generation iPod Touch. I should have thought of
that..."there's an app for that" too I guess.

Out of the applications you have, is there any one that stands out above
the rest, whether free or not?

William

I gotta get me one of those. Still listening (and watching) my 30 gig
Ipod. Looked for the new 64 gig I Touch, pricey! But not out of my price
range even with the 3G option.



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[William R. Walsh]

Hi!

I don't think you need to worry about biasing a hybrid module. Those
things are STK-something right?

In this case, it's an STK-2038 II module that is used.

This receiver has something called "Computer Drive". It's not clear what the
"Computer" in use (a 4-bit Matsushita microcontroller) actually *does*, but
I really think it is only watching the input signal level, temperature (via
a tripping-type sensor set to 60C! Ouch!) and triggering the "preheat"
operation, operating some LEDs and generally looking pretty. (My only other
"Computer Drive" receiver, an SA-560, doesn't seem to *have* the "Computer
Drive" IC. It has only a small circuit that switches on for a time at
startup to "preheat" the power transistors.) I smell marketing and maybe
some "audiophoolery" here...?

There's also "New Class A Synchro Bias" which I take to mean (after having
done some reading) that the transistors in the amplifier are prevented from
ever switching off completely when the unit is in operation. If I'm not
mistaken, wouldn't that result in a lot of needless heat dissipation and a
stressful operating environment for the STK-2038 module?

There are what appear to be bias adjustment pots on the main board in what
little outboard supporting circuitry the amplifier uses. So far as I know,
they're not mentioned in the service manual, so my guess is "no adjustments
intended".

William