Hello all...

Just thought I'd drop in and provide a quick status update. I learned a few
things along the way:

1. STK-2038 and 2038 II modules are not at all the same. Someone (not here)
told me they were electrically compatible with each other, and this is not
so. The STK-2038II has more pins and seems to be less commonly available.

A few people pointed me in various directions, and one pointed me to a new
old stock STK-2048 II module, still sealed in the factory wrapping. I opted
for that one; it's used in the next model up (the SA-410).

2. Nothing more than installing the new module was required. Everything is
playing great now.

3. I'll never push the unit *that* hard again (turned it up about halfway
and that was when it started to fold).

4. The internal protection circuit absolutely will NOT save your speakers if
anything goes wrong with the power amplifier. I was using an outboard
speaker protection device and it did the job when the hybrid module went the
rest of the way.

5. Computer Drive and its method of forcing the transistors in the hybrid to
remain turned on to some degree at all times seems to make them run really
HOT. Every SA-310 and 410 I've ever seen gets very hot, especially when
idling. I'm going to install a fan. The heatsink becomes ridiculously hot
within ten minutes of operation, so hot that it can't be touched. I don't
think this can be good for the hybrid.

I learned a lot and I appreciate everyone's help and commentary from this
group. I have no intention of finding out, but I do wonder what Computer
Drive actually *does* when the 60C temperature sensor attached to it
trips...? Honestly I'm surprised it hasn't--a 50C device is at least
touchable. This really isn't. And all the service manual says is that the
"Thermal" LED on the Computer Drive Monitor goes out when this happens.

William

William R. Walsh m wrote
in message ...
Hello all...

Just thought I'd drop in and provide a quick status update. I learned a
few
things along the way:

1. STK-2038 and 2038 II modules are not at all the same. Someone (not
here)
told me they were electrically compatible with each other, and this is not
so. The STK-2038II has more pins and seems to be less commonly available.

A few people pointed me in various directions, and one pointed me to a new
old stock STK-2048 II module, still sealed in the factory wrapping. I
opted
for that one; it's used in the next model up (the SA-410).

2. Nothing more than installing the new module was required. Everything is
playing great now.

3. I'll never push the unit *that* hard again (turned it up about halfway
and that was when it started to fold).

4. The internal protection circuit absolutely will NOT save your speakers
if
anything goes wrong with the power amplifier. I was using an outboard
speaker protection device and it did the job when the hybrid module went
the
rest of the way.

5. Computer Drive and its method of forcing the transistors in the hybrid
to
remain turned on to some degree at all times seems to make them run really
HOT. Every SA-310 and 410 I've ever seen gets very hot, especially when
idling. I'm going to install a fan. The heatsink becomes ridiculously hot
within ten minutes of operation, so hot that it can't be touched. I don't
think this can be good for the hybrid.

I learned a lot and I appreciate everyone's help and commentary from this
group. I have no intention of finding out, but I do wonder what Computer
Drive actually *does* when the 60C temperature sensor attached to it
trips...? Honestly I'm surprised it hasn't--a 50C device is at least
touchable. This really isn't. And all the service manual says is that the
"Thermal" LED on the Computer Drive Monitor goes out when this happens.

William




If the "outboard speaker protection device " is a "crowbar" how do you know
it was not a failure in that which knocked out the amp ?

On Wed, 01 Sep 2010 02:27:41 -0500, William R. Walsh wrote:

Hello all...

Just thought I'd drop in and provide a quick status update. I learned a
few things along the way:

1. STK-2038 and 2038 II modules are not at all the same. Someone (not
here) told me they were electrically compatible with each other, and
this is not so. The STK-2038II has more pins and seems to be less
commonly available.

A few people pointed me in various directions, and one pointed me to a
new old stock STK-2048 II module, still sealed in the factory wrapping.
I opted for that one; it's used in the next model up (the SA-410).

Boy does THAT have a familiar ring.



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

Hi!

If the "outboard speaker protection device " is a "crowbar" how
do you know it was not a failure in that which knocked out the
amp ?

The device in question opens the circuit by tripping a relay (one per
channel).

The left channel of the amplifier was already dying before I was using
it anyway. At first it got weak and distorted when I turned up the
volume. It would come back to working order if I turned it back down.

Then it stayed broken, with the weak and distorted audio on the left
channel. Around that time, I put the good speakers away, got some
crappy ones and decided that I'd rather not smell them burning up.

It played for a while beyond that and then "click" ... the relay
tripped.

William

Hi!

Boy does THAT have a familiar ring.

I don't think I know what you are getting at.

William

Computer Drive and its method of forcing the transistors in the
hybrid to remain turned on to some degree at all times seems
to make them run really HOT. Every SA-310 and 410 I've ever
seen gets very hot, especially when idling. I'm going to install
a fan. The heatsink becomes ridiculously hot after ten minutes
of operation, so hot it can't be touched. I don't think this can
be good for the hybrid.

Some years ago an audiophile reviewer complained that an amplifier's
heatsinks got unduly hot. The manufacturer replied that that was the purpose
of the heatsink, to remove heat from the output stage.

Although this makes a sort of sense, the fact is that an extremely hot
heatsink -- except when the amplifier is driven to the point of maximum
dissipation, which I believe is about 35% of clipping power for a weakly
biased class-AB amp -- suggests that the heatsink isn't big enough.

On Wed, 01 Sep 2010 06:40:32 -0700, William R. Walsh wrote:

Hi!

Boy does THAT have a familiar ring.

I don't think I know what you are getting at.

William

The STK subbing. That actually went on a lot with so many different
models of those receivers and amps.



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

Hi!

The manufacturer replied that that was the purpose
of the heatsink, to remove heat from the output stage.

I'd certainly agree with that.

Although this makes a sort of sense, the fact is that an extremely hot
heatsink -- except when the amplifier is driven to the point of maximum
dissipation, which I believe is about 35% of clipping power for a weakly
biased class-AB amp -- suggests that the heatsink isn't big enough.

It may very well not be big enough. When I removed the old module, I
noticed that the factory's application of heatsink compound was
basically "glob it on there, the thicker the better".

I cleaned all of that mess off, followed by rubbing down the backplate
of the new module and the mating surface on the heatsink with 99%
isopropyl alcohol to assure that both were very clean. The old
compound was dried up anyway. Might as well do it right. Then I did it
up with a *thin* layer of Radio Shack's basic heatsink compound,
applied to the back of the module with a credit card slice. Just a
very little of the compound squirted out from the top when I screwed
the new module back into place...a lot less than the excess "blob"
that had been resting on the old module's top.

I have no reason to believe that the hybrid module was ever replaced
prior to this. My other, similar Technics receivers also show signs of
"too much heatsink compound".

This seems to be doing a better job. With the old module, I remember
its plastic casing getting hot along with the heatsink. The new module
gets the heatsink hotter while its plastic casing stays much cooler.
This could mean a lot of things. I take it to mean the heatsink is
being more effectively utilized now.

The receiver itself is a slimline unit:
http://www.vintagetechnics.info/receivers/sa310.htm
which limits any possibility for modification. I definitely do think I
could take two small DC fans, borrow a little power from the 28.5 volt
tap on the transformer, run it through a rectifier and greatly reduce
the heat problem. As each of the 28.5 volt taps power the audio
amplifier, one easily ought to have enough power to spare for some
little fans.

I also have an SA-210 and SA-120. These have similar power output to
the SA-310, use the "Series I" Sanyo STK-XXXX modules and seem to run
in conventional Class AB mode (no Computer Drive or "synchro bias").
Both of them put out a LOT less heat when idling or working hard.

William

Hi!

The STK subbing. That actually went on a lot with so many different
models of those receivers and amps.

I read somewhere that some manufacturers even did this when building a
new receiver, using a bigger module where a smaller one had been
called for.

This new module went into place very well. I did a better job of
cleaning out the through-holes than I first thought, although I did
have one pin miss its hole and get a little bit bent up in the
process. It was an easy fix. Soldering the new module in also proved
to be pretty easy.

William

On Wed, 01 Sep 2010 08:25:36 -0700, William R. Walsh wrote:

Hi!

The STK subbing. That actually went on a lot with so many different
models of those receivers and amps.

I read somewhere that some manufacturers even did this when building a
new receiver, using a bigger module where a smaller one had been called
for.

This new module went into place very well. I did a better job of
cleaning out the through-holes than I first thought, although I did have
one pin miss its hole and get a little bit bent up in the process. It
was an easy fix. Soldering the new module in also proved to be pretty
easy.

William

I've replaced several dozen of those back in the 80s when I worked for a
person who was factory authorized by 10 major brands. I remember writing
down what I needed and getting replacements with more pins or less pins.
Then having to look through Panasonic tech literature and choosing
replacements by physical/electrical description and ignoring the STK
numbers to some extent. Finally had hand written my own cross reference.



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

A follow up to my follow up...one thing that I've noticed is how hot the
various "Computer Drive" receivers run even when operating normally. So I
found my IR non-contact thermometer and had a look at the newly repaired
SA-310.

At idle for around 20 minutes, the temperature of the heatsink had risen to
130 degrees Fahrenheit (54 degrees Celsius)! And the unit was just *idling*.
The hybrid's internals are probably a good ten degrees hotter still. Call me
picky, but that is not what I'd call the recipe for semiconductor longevity!
Ouch! (Just how did the last hybrid--presumably the original--manage to live
so long?)

By comparison, the Class AB SA-120 (with its identical power rating) idles
around 88-90 degrees F after being on for a while. Its STK module also has a
much smaller heatsink.

For now I have made a "contraption" consisting of a DC muffin fan affixed to
the bottom of the SA-310 using bubble wrap on the corners to stop the case
from vibrating. With this setup, and two books at each end of the receiver
to give the fan clearance, the temperature never gets above 105 degrees F
even with the cover on. Most areas of the heatsink are slightly cooler than
that (in the high 80s or lower-middle 90s).

Later, when I get some free time, I plan to install two small fans on the
heatsink, helping to pull air over it and hopefully keep that hybrid alive
and comfortable.

It has been suggested that minorly violent and mostly non-destructive
disassembly of an STK-series hybrid amplifier is possible. Some people even
make the claim of having repaired the bad parts within. I may just have to
try it if the old hybrid hasn't walked off yet.

The DC offset as measured at the speaker terminals (no source playing, no
speakers attached of course) is between 8-12mV for both channels now. I
believe the unit to be fixed. :-)

William

On Wed, 01 Sep 2010 23:39:30 -0500, William R. Walsh wrote:

A follow up to my follow up...one thing that I've noticed is how hot the
various "Computer Drive" receivers run even when operating normally. So
I found my IR non-contact thermometer and had a look at the newly
repaired SA-310.

At idle for around 20 minutes, the temperature of the heatsink had risen
to 130 degrees Fahrenheit (54 degrees Celsius)! And the unit was just
*idling*. The hybrid's internals are probably a good ten degrees hotter
still. Call me picky, but that is not what I'd call the recipe for
semiconductor longevity! Ouch! (Just how did the last hybrid--presumably
the original--manage to live so long?)

By comparison, the Class AB SA-120 (with its identical power rating)
idles around 88-90 degrees F after being on for a while. Its STK module
also has a much smaller heatsink.

For now I have made a "contraption" consisting of a DC muffin fan
affixed to the bottom of the SA-310 using bubble wrap on the corners to
stop the case from vibrating. With this setup, and two books at each end
of the receiver to give the fan clearance, the temperature never gets
above 105 degrees F even with the cover on. Most areas of the heatsink
are slightly cooler than that (in the high 80s or lower-middle 90s).

Later, when I get some free time, I plan to install two small fans on
the heatsink, helping to pull air over it and hopefully keep that hybrid
alive and comfortable.

It has been suggested that minorly violent and mostly non-destructive
disassembly of an STK-series hybrid amplifier is possible. Some people
even make the claim of having repaired the bad parts within. I may just
have to try it if the old hybrid hasn't walked off yet.

The DC offset as measured at the speaker terminals (no source playing,
no speakers attached of course) is between 8-12mV for both channels now.
I believe the unit to be fixed. :-)

William

Do you have the temp specs of the replacement STK?



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

Hi!

Do you have the temp specs of the replacement STK?

No, I don't. I've never even been able to find a datasheet for either
of the STK-2038 II or STK-2048 II modules, nor anything that seemed
closely related.

Of those I did find (for the Series I modules), I don't recall seeing
any temperature information. But it's been a while and those copies
were pretty illegible.

I was only a little bit surprised to find that something like this
wasn't included with the replacement. In this case, the replacement
module is actually a new old stock genuine Panasonic replacement.

William

On Thu, 02 Sep 2010 06:33:12 -0700, William R. Walsh wrote:

Hi!

Do you have the temp specs of the replacement STK?

No, I don't. I've never even been able to find a datasheet for either of
the STK-2038 II or STK-2048 II modules, nor anything that seemed closely
related.

Of those I did find (for the Series I modules), I don't recall seeing
any temperature information. But it's been a while and those copies were
pretty illegible.

I was only a little bit surprised to find that something like this
wasn't included with the replacement. In this case, the replacement
module is actually a new old stock genuine Panasonic replacement.

William

A PDF at alldatasheet.com shows a 2040 as having a max junction
temp of 150 C. That's 302 F. I would guess most are the same.



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

Hi!

A PDF at alldatasheet.com shows a 2040 as having a max
junction temp of 150 C. That's 302 F. I would guess most are
the same.

I don't think the module would live very long at that temperature. The
behavior of Computer Drive seems to keep it hot, too. I've always been
of the school of thought that said "keep your silicon devices cool and
they will live longer".

Then again, I have no reason to believe that the old module was ever
replaced, and it did survive 27 years worth of usage...

I don't know about the relative toughness of STK-XXXX amplifier
modules. I've always been of the impression that they are not always
robust. Yet it seems that people have abused them and gotten away with
it. And outside of this one receiver, I've never lost one...

William

On Thu, 02 Sep 2010 12:36:01 -0700, William R. Walsh wrote:

Hi!

A PDF at alldatasheet.com shows a 2040 as having a max junction temp of
150 C. That's 302 F. I would guess most are the same.

I don't think the module would live very long at that temperature. The
behavior of Computer Drive seems to keep it hot, too. I've always been
of the school of thought that said "keep your silicon devices cool and
they will live longer".

Then again, I have no reason to believe that the old module was ever
replaced, and it did survive 27 years worth of usage...

I don't know about the relative toughness of STK-XXXX amplifier modules.
I've always been of the impression that they are not always robust. Yet
it seems that people have abused them and gotten away with it. And
outside of this one receiver, I've never lost one...

William

I've always thought the PCDPP to be robust. Your right they wouldn't last
too long at a max Jt of 150C but most survive well at a working temp of
105C.

Panasonic, Sanyo, Sansui, Pioneer Yamaha etc used them. Rear Projection
TV sets used them for convergence amps which I consider the hardest
working part of the set. So there must be some reason these were chosen
other than a convenient package. If you use the correct amount of heat
sink compound spread evenly and torque them down properly provided the
heat sink has enough surface area there is no reason for these to be
problematic. Like you said the originals in your SA lasted 27 years even
biased class A.



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