Technics SA-310 Intermittent Weak Left Channel
William R. Walsh
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
Meat Plow
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
William R. Walsh
> 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
Mark Zacharias
wrote in message news:Tb-dnXWkarbnCfXR...@mchsi.com...
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
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.
Arfa Daily
"Mark Zacharias" <mark_za...@sbcglobal.net> wrote in message
news:4c691e79$0$14508$c3e...@news.astraweb.com...
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
> 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
> 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
Meat Plow
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.
William R. Walsh
> 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
You could always swap the caps since each channel has its own pair. Or
just shotgun them all and cross your fingers.
Arfa Daily
"William R. Walsh" <newsg...@idontwantjunqueemail.walshcomptech.com>
wrote in message news:ZbqdnWGcB-688fTR...@mchsi.com...
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" <newsg...@idontwantjunqueemail.walshcomptech.com>
wrote in message news:4pWdnS6RcN1N8PTR...@mchsi.com...
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
news:epkao.20214$Dt3.13835@hurricane...
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
> 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
> 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
Meat Plow
I don't think you need to worry about biasing a hybrid module. Those
things are STK-something right?
Meat Plow
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.
William R. Walsh
> 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
William R. Walsh
> 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
William R. Walsh
> 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.
I bought a first-gen unit at a severe discount when the second generation
ones came out. It doesn't really matter to me if I'm "one step behind".
Even as nice of a piece of equipment as it is, there's nothing about it that
screams "killer app". I've only ever used it very occasionally to browse the
web at home when a computer wasn't convenient or to play video. I don't care
much that it will never see iOS 4.
I found a well received and free audio frequency generation app, but the
iTMS is somehow dorked up at the moment and convinced that my credit card
will be expiring soon (in 2013?). Not quite.
William
Mark Zacharias
wrote in message news:xbWdnVB1kd3AGvHR...@mchsi.com...
You are correct that Panasonic added an SVI prefix to the STK modules' part
numbers - I had forgotten that!
The later models from approximately the 1990's used Panasonic (Matsushita)
built outputs with original SVI numbering on the modules themselves.
The chips were very different and not at all interchangeable. Also, the SVI
modules were very expensive, often leading to repair work being declined by
the customer.
The STK's almost never had any external biasing - I might have seen that
once in 35 years. Occasionally there could be an external resistor burned.
Normally you just replace the module and fuse if necessary and enjoy!
Mark Z.
Meat Plow
I don't know why you would need to pre-heat a hybrid module. Must be a
sales gimmick. If I still worked for a Matsu authorized repair center I'd
be better able to answer. Having not been active in warranty repair for
them in over 27 years I don't recall exactly the verifications after
repair procedure we had to do. I would almost bet the farm that they
won't need adjustment.
Meat Plow
I currently have a 30gb video Ipod. And an Ipod Shuffle. I'm pretty sure
that 32 gigs will serve me fine. My video Ipod has some dark lines in the
screen going from right to left. Not much of a deal unless you want to
watch a video. Funny thing is the lines are in the back light. They don't
show when looking at the display with the back light off. My music and
video library is over 100 gb. I frequently change the music and videos.
Currently have 10 gigs of music on the 30 and 10 gigs of video. Made a TV-
out cable so I can watch video on TV. And the picture is pretty damn
good. I've read some pros and cons for the 64 gb model. Don't care for
some of the cons so I will probably buy a 32. One app I like is called
Scanner911. It gets its audio from radioreference.com. People donate
scanner streaming to the site. You can listen on the PC. Around here all
of the departments except our local public safety switch to APCO-25/EDACS
800mhz trunked encrypted so I can no longer listen in on the sheriff/
state patrol. Someone in this area feeds Radioreference with a Uniden 996
scanner capable of receiving that traffic. I can pick it up on the PC or
on my netbook also. Being a Ham for 20 years now it's always been a hobby
of listening to police and fire along with SW.
Arfa Daily
"William R. Walsh" <newsg...@idontwantjunqueemail.walshcomptech.com>
wrote in message news:bIadnVM7xZ5rHPHR...@mchsi.com...
I have two on there. One is called "FreqGen" and the other is called
"Oscillatr Free" actually spelt like that. Both are much the same in
functionality, but I think that FreqGen is a bit nicer to use.
Arfa
Meat Plow
I still use my old Leader from the 80s. It's coupled to my freq counter
if I need to be precise.
Arfa Daily
"Meat Plow" <mhy...@yahoo.com> wrote in message
news:pan.2010.08...@hahahahahahahah.nutz.I.am...
For most bench work, I use a Ferrograph Pro Recorder Test Set that has a
rather nice frequency and amplitude stabilised multi decade oscillator in
it, but I also have an old and cherished Marconi Instruments "R-C
Oscillator" which uses tubes as I recall, although it's been a long time
since I've been inside it. Looks like it probably dates from the 60s.
Arfa
Meat Plow
Since I don't have my I Touch yet I recorded some test tones on my Sharp
MD, transferred to PC and uploaded to my video IPod :) How's that for
ingenuity?
Arfa Daily
Nothing more or less than I would have expected from you, Meat ! It's
lateral thinking like this that sets us old timers apart from today's 'black
box' kids ... d;~}
Arfa
Arfa Daily
"Arfa Daily" <arfa....@ntlworld.com> wrote in message
news:koYbo.106547$KP3.4319@hurricane...
Hey Meat, just saw your response to the 'car windshield fitter story' whilst
I was cruisin' on uk.rec.cars.maintenance. Which of the many cross-posted
groups were you responding from ? Didn't see any in the list that looked
like the sort of place I'd find you lurking ... !
Just as a matter of interest, I'm sure I remember having a windshield
replaced in one of our cars a few years back, and the fitter actually had to
take the vehicle away to a facility to do the job, as it was an aerodynamic
screen glued in rather than being just 'traditionally' fitted in a rubber
seal. I feel that I can recall the fitter saying that the replacement glue
had to be 'baked' under IR lamps for something like 2 hours, and the vehicle
could not, as a result of this, be moved for at least that amount of time.
Arfa
Meat Plow
I think that 24hoursupport.helpdesk was in the lineup.
> Just as a matter of interest, I'm sure I remember having a windshield
> replaced in one of our cars a few years back, and the fitter actually
> had to take the vehicle away to a facility to do the job, as it was an
> aerodynamic screen glued in rather than being just 'traditionally'
> fitted in a rubber seal. I feel that I can recall the fitter saying that
> the replacement glue had to be 'baked' under IR lamps for something like
> 2 hours, and the vehicle could not, as a result of this, be moved for at
> least that amount of time.
>
> Arfa
Mine was just glued in with black Silicone rubber. Hardest part was
scraping the old away. To remove, the molding came off in about a minute
or so, a wire was passed through the old glue and glass to cut the seal.
That took maybe 3 minutes. The glass was fitted with a couple suction
cups and lifted off. It took maybe 10 minutes to scrape th remaining
silicone away and the 5 to run a bead of new silicone plus some other
rubber thing I guess was an additional gasket. Then the new glass was
laid down, pressed in and molding reinstalled. I didn't put a stopwatch
on the guy but I'm sure it wasn't more than 15 minutes from start to
finish. And the new glass came from Pilkington over in your neck of the
woods. I guess they make most of the glass for the US industry because
my Chevy Trailblazer has Pilk glass in it.