technics amp SU-Z200 low volume problem

[b]

I've just found this technics amp in a skip, I'd say mid 80s vintage.,
along with the rest of the system!

The amp only outputs at very low volume - and then for a short while.
Also if you push it up more than 3, it cuts out and needs a power
cycle. Both channels are affected. I noticed R701, 702 (470R)and D701,
702 (Bzv85c) get very hot and there is evidence of some scorching on
the pcb. Might change those diodes.

It uses an STK 4152 II, pretty typical design of the period.

The headphone o/p works normally.

Any suggestions before I go on a cap change oin the o/p stage? anyone
have a schematic?
cheers
B.

 

[Franc Zabkar]

On Tue, 18 May 2010 15:04:03 -0700 (PDT), b
<reverend_rogers@yahoo.com> put finger to keyboard and composed:

It uses an STK 4152 II, pretty typical design of the period.

FWIW, there is application circuit in the datasheet:
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-316/586035.pdf
http://www.acust.narod.ru/files/PDF/STK4152.PDF

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Archon]

On 5/19/2010 4:44 PM, b wrote:

On 19 mayo, 00:24, Franc Zabkar<fzab...@iinternode.on.net> wrote:
On Tue, 18 May 2010 15:04:03 -0700 (PDT), b
reverend_rog...@yahoo.com> put finger to keyboard and composed:

It uses an STK 4152 II, pretty typical design of the period.

FWIW, there is application circuit in the datasheet:http://www.datasheetarchive.com/pdf-datasheets/Datasheets-316/586035.pdfhttp://www.acust.narod.ru/files/PDF/STK4152.PDF

took a look at that, thanks. Unfortunately there is nothing connected
to the mute pin (6) on this amp, so that ruled out a relatively easy
line to pursue.
I've changed most of the caps around the subcircuits of the IC to no
avail. It's looking as if the IC is shot, and it seesm to be NLA.....
-B

Ebay #380189378364

JC

 

[Dave M]

Archon wrote:

On 5/19/2010 4:44 PM, b wrote:
On 19 mayo, 00:24, Franc Zabkar<fzab...@iinternode.on.net> wrote:
On Tue, 18 May 2010 15:04:03 -0700 (PDT), b
reverend_rog...@yahoo.com> put finger to keyboard and composed:

It uses an STK 4152 II, pretty typical design of the period.

FWIW, there is application circuit in the
datasheet:http://www.datasheetarchive.com/pdf-datasheets/Datasheets-316/586035.pdfhttp://www.acust.narod.ru/files/PDF/STK4152.PDF

took a look at that, thanks. Unfortunately there is nothing connected
to the mute pin (6) on this amp, so that ruled out a relatively easy
line to pursue.
I've changed most of the caps around the subcircuits of the IC to no
avail. It's looking as if the IC is shot, and it seesm to be NLA.....
-B

Ebay #380189378364

JC

Also available from Consolidated Electronics at
http://www.ceitron.com/semi/semi.phtml?part=STK4152

--
David
dgminala at mediacombb dot net

 

[b]

On 19 mayo, 00:24, Franc Zabkar <fzab...@iinternode.on.net> wrote:

On Tue, 18 May 2010 15:04:03 -0700 (PDT), b
reverend_rog...@yahoo.com> put finger to keyboard and composed:

It uses an STK 4152 II, pretty typical design of the period.

FWIW, there is application circuit in the datasheet:http://www.datasheetarchive.com/pdf-datasheets/Datasheets-316/586035.pdfhttp://www.acust.narod.ru/files/PDF/STK4152.PDF

took a look at that, thanks. Unfortunately there is nothing connected
to the mute pin (6) on this amp, so that ruled out a relatively easy
line to pursue.
I've changed most of the caps around the subcircuits of the IC to no
avail. It's looking as if the IC is shot, and it seesm to be NLA.....
-B

 

[Franc Zabkar]

On Wed, 19 May 2010 13:44:20 -0700 (PDT), b
<reverend_rogers@yahoo.com> put finger to keyboard and composed:

It's looking as if the IC is shot, and it seesm to be NLA.....

http://www.bdent.com/search/part.jsp?partnum=STK4152II

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[William R. Walsh]

Hi!

It's looking as if the IC is shot, and it seesm to be NLA.....

It's a common problem. In a lot of these 80s Technics amplifiers, the
Sanyo power amplifier IC goes bad. I've come to believe that they are
somewhat "failure prone". Interestingly enough, it seems that other
designs using these modules were more reliable--I have some Aiwa "all
in one" stereo systems and a little Pioneer receiver that use the
Sanyo module. None of these run as hot as do the Technics
receivers...perhaps another data point?

Despite being played hard at times, these units have never caused any
trouble. Of course, most of the time I happened to come across such
older Technics gear, it had already been treated badly.

There is a more sinister problem--the Sanyo module integrates speaker
protection through electronic means. The idea is that if one of the
final transistors breaks, this electronic protection circuit will
break the path between module and speaker so that your speaker does
not become exposed to a power supply rail and burn out. Unfortunately,
the protection circuit is usually destroyed and the speaker burns out.

I thought all of the Technics amplifiers that used these hybrid
modules relied on the electronic protection. After searching for a
long time to find a nice one in working condition, I discovered an
SA-929 receiver (also based on a house numbered Sanyo integrated
amplifier module) that has an outboard DC protection relay. This
should save the speakers if anything goes wrong.

I also found that the relay itself had pitted contacts, resulting in
intermittent audio output from one speaker or another. Cleaning the
relay contacts resolved this problem, but in the process I found bad
solder joints that were aggravated by my opening the relay.

http://www.youtube.com/watch?v=K0cObJ7o8vE (SA-929)
http://www.youtube.com/watch?v=sgdTnBU0_N0 (SA-929 repairs)

I have seen at least one other report that suggested bad solder on the
protection relay's coil contacts was to blame for intermittent audio.

If you have enough room and another partially broken part, you might
try this for a fix (different amp, similar module):

http://john.ccac.rwth-aachen.de:8000/misc/rr100rep/

I've never tried it, nor is that my page.

William

 

[b]

On 20 mayo, 15:40, "William R. Walsh" <wm_wa...@hotmail.com> wrote:

Hi!

It's looking as if the IC is shot, and it seesm to be NLA.....

It's a common problem. In a lot of these 80s Technics amplifiers, the
Sanyo power amplifier IC goes bad. I've come to believe that they are
somewhat "failure prone". Interestingly enough, it seems that other
designs using these modules were more reliable--I have some Aiwa "all
in one" stereo systems and a little Pioneer receiver that use the
Sanyo module. None of these run as hot as do the Technics
receivers...perhaps another data point?

Despite being played hard at times, these units have never caused any
trouble. Of course, most of the time I happened to come across such
older Technics gear, it had already been treated badly.

There is a more sinister problem--the Sanyo module integrates speaker
protection through electronic means. The idea is that if one of the
final transistors breaks, this electronic protection circuit will
break the path between module and speaker so that your speaker does
not become exposed to a power supply rail and burn out. Unfortunately,
the protection circuit is usually destroyed and the speaker burns out.

I thought all of the Technics amplifiers that used these hybrid
modules relied on the electronic protection. After searching for a
long time to find a nice one in working condition, I discovered an
SA-929 receiver (also based on a house numbered Sanyo integrated
amplifier module) that has an outboard DC protection relay. This
should save the speakers if anything goes wrong.

I think the reason could be the supply voltage. Seems they can take
anything from 27 to 40-odd volts, which might explain the varied
reliability.

I too was surprised at the lack of protection visbile in this amp.
there's only a resistor separating the o/p from the speakers!
ironiocally in this case, the protection seems to kick in far too
early - muting the o/p even when the sound is barely audible.

i just took a look in my spres box and found an STK 4121 II which,
according to a quick look at the dateasheet here :
http://www.datasheetcatalog.org/datasheets2/10/106635_1.pdf
has the same pinout as my 4152 ii

Might this work as a drop in replacement? the output would only be 15
watts, but better than nothing.....
-B

 

[William R. Walsh]

Hi!

I think the reason could be the supply voltage. Seems they can
take anything from 27 to 40-odd volts, which might explain
the varied reliability.

Hmm...that is a thought. It might also explain why these little
receivers run so darn hot. Interestingly, mine seems to run hottest
when idle.

I too was surprised at the lack of protection visbile in this amp.
there's only a resistor separating the o/p from the speakers!
ironiocally in this case, the protection seems to kick in far too
early - muting the o/p even when the sound is barely audible.

Be glad it does, but please don't use it with valuable speakers or
depend upon it to work correctly. All too often it...doesn't. The
result is smoke from your speakers.

That is why I was so surprised that the SA-929 receiver I found had an
honest to goodness relay. What motivated Technics to use one there
when they didn't use one in the other models I've seen?

Might this work as a drop in replacement? the output would only
be 15 watts, but better than nothing.....

As they're all pin compatible, I think you can pretty much swap them
at will as long as the voltage ranges are the same for each part. You
probably couldn't get away with a bigger module (it would surely
overtax the power supply) but a smaller one ought to work, especially
if not driven hard or into inefficient speakers. The page that I
linked to suggests that sometimes a larger module was used at reduced
voltage and current levels.

You'd be surprised what "just" fifteen watts worth of output power
will do in terms of volume output.

If you try it, please do post back!

William

 

[b]

On May 21, 2:45 pm, "William R. Walsh" <wm_wa...@hotmail.com> wrote:

If you try it, please do post back!

William

Just soldered in the other ic and guess what? same problem!
a tricky one this, as there aren't that many things on the pcb common
to both channels. will keep looking...
-B

 

[William R. Walsh]

Hi!

Just soldered in the other ic and guess what? same problem!

How interesting! (Okay, maybe not...)

I wouldn't think that the replacement module would be broken in
exactly the same way as the first, unless I were doing the work. (At
times, my life is a comedy.) I suppose that something could be loading
down the power supply or the output of the amplifier module. I'm not
sure what it would be.

William

 

[b]

On 24 mayo, 17:47, "William R. Walsh" <wm_wa...@hotmail.com>

I wouldn't think that the replacement module would be broken in
exactly the same way as the first, unless I were doing the work. (At
times, my life is a comedy.) I suppose that something could be loading
down the power supply

That's what I am beginning to suspect, as it is pretty much the only
common thing left! A few days back, I did also notice that as I pushed
the vol. up by the small amount I could before it muted, that the
sound appeared to be a *bit* distorted (as in overloaded type
distortion).... or did I imagine it?!

I've had to 'park' this one for now as other projects are piling up,
but will probably return to it before long. watch this space....
-B

 

[Mark Zacharias]

"b" <reverend_rogers@yahoo.com> wrote in message
news:d799cabb-0817-41e3-93a7-b77ec68e682f@q13g2000vbm.googlegroups.com...

On 24 mayo, 17:47, "William R. Walsh" <wm_wa...@hotmail.com

I wouldn't think that the replacement module would be broken in
exactly the same way as the first, unless I were doing the work. (At
times, my life is a comedy.) I suppose that something could be loading
down the power supply

That's what I am beginning to suspect, as it is pretty much the only
common thing left! A few days back, I did also notice that as I pushed
the vol. up by the small amount I could before it muted, that the
sound appeared to be a *bit* distorted (as in overloaded type
distortion).... or did I imagine it?!

I've had to 'park' this one for now as other projects are piling up,
but will probably return to it before long. watch this space....
-B

Really though, it's likely the problem is just somewhere else. Replacing the
amp module did gain valuable information though, so it's not a total loss.
That's how I look at these situations anyway...

Mark Z

 

[b]

On 25 mayo, 12:19, "Mark Zacharias" <mark_zachar...@sbclobal.net>
wrote:

"b" <reverend_rog...@yahoo.com> wrote in message

news:d799cabb-0817-41e3-93a7-b77ec68e682f@q13g2000vbm.googlegroups.com...



On 24 mayo, 17:47, "William R. Walsh" <wm_wa...@hotmail.com

I wouldn't think that the replacement module would be broken in
exactly the same way as the first, unless I were doing the work. (At
times, my life is a comedy.) I suppose that something could be loading
down the power supply

That's what I am beginning to suspect, as it is pretty much the only
common thing left! A few days back, I did also notice that as I pushed
the vol. up by the small amount I could before it muted, that the
sound appeared to be a *bit* distorted (as in overloaded type
distortion).... or did I imagine it?!

I've had to 'park' this one for now as other projects are piling up,
but will probably return to it before long. watch this space....
-B

Really though, it's likely the problem is just somewhere else. Replacing the
amp module did gain valuable information though, so it's not a total loss.
That's how I look at these situations anyway...

Mark Z

Same here. At the end of the day this thing cost me nothing and is
worth little -I'm doing this out of curiosity, so if I learn
something from it then so much the better.
ISTR the replacement module was taken from something working (a
samsung midi system or something), but I could be mistaken (it was at
least 6 years back) so will keep an open mind on that front
-B

 

[John Robertson]

b wrote:

On May 21, 2:45 pm, "William R. Walsh" <wm_wa...@hotmail.com> wrote:

If you try it, please do post back!

William

Just soldered in the other ic and guess what? same problem!
a tricky one this, as there aren't that many things on the pcb common
to both channels. will keep looking...
-B

Any electrolytic capacitors? Have you tried replacing them - did not see
anything relating to that so far in this thread...

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[b]

On 26 mayo, 03:56, John Robertson <s...@flippers.com> wrote:

Any electrolytic capacitors? Have you tried replacing them - did not see
anything relating to that so far in this thread...

Hi John,

I changed all the ones near the ic, except the two large filter caps
in the bridge rectifier and one 50v non polar cap which I have no
spare for. There are a few I haven't changed in the phono preamp and
headphone amp as they don't appear to be directly related to the
problem.
-B