Hello all...

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and repairing
the protection relay, I noticed that there is a wire coming from the
printboard that holds both the AC power input and accessory outlet
connections going to the "speaker -" connector for the "B" speaker
terminals.

There is a resistor inline with the wire coming from the AC wiring board.

I've never noticed anything like this in a stereo receiver before. As the
previous owner seems to have been very meticulous about packing it up, I
believe the non-polarized power cord set is original to the unit.

What would this do? Is it dangerous?

William

"William R. Walsh"

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and
repairing
the protection relay, I noticed that there is a wire coming from the
printboard that holds both the AC power input and accessory outlet
connections going to the "speaker -" connector for the "B" speaker
terminals.

There is a resistor inline with the wire coming from the AC wiring board.


** Resistors have values - did you not check it ??


I've never noticed anything like this in a stereo receiver before.


** Certainly unusual.


What would this do?


** Tell us the value of the resistor.

Betcha it is about 10 Mohms.



...... Phil

On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh"
m wrote:

Hello all...

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and repairing
the protection relay, I noticed that there is a wire coming from the
printboard that holds both the AC power input and accessory outlet
connections going to the "speaker -" connector for the "B" speaker
terminals.

There is a resistor

What value?

inline with the wire coming from the AC wiring board.

Where on the AC wiring board? The ground? The neutral? The hot wire?
Where?


I've never noticed anything like this in a stereo receiver before.

You've never looked then...

As the
previous owner seems to have been very meticulous about packing it up, I
believe the non-polarized power cord set is original to the unit.

What would this do? Is it dangerous?

William

On Sun, 23 May 2010 23:03:29 -0500, William R. Walsh wrote:

Hello all...

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and
repairing the protection relay, I noticed that there is a wire coming
from the printboard that holds both the AC power input and accessory
outlet connections going to the "speaker -" connector for the "B"
speaker terminals.

There is a resistor inline with the wire coming from the AC wiring
board.

I've never noticed anything like this in a stereo receiver before. As
the previous owner seems to have been very meticulous about packing it
up, I believe the non-polarized power cord set is original to the unit.

What would this do? Is it dangerous?

William

Got schematic?

On 24/05/2010 05:03, William R. Walsh wrote:
Hello all...

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and repairing
the protection relay, I noticed that there is a wire coming from the
printboard that holds both the AC power input and accessory outlet
connections going to the "speaker -" connector for the "B" speaker
terminals.

There is a resistor inline with the wire coming from the AC wiring board.


It's strange. Skip forward 8m:05s on following video.

http://www.youtube.com/watch?v=sgdTnBU0_N0

No idea :-|

--
Adrian C

On 24/05/2010 14:37, Adrian C wrote:

It's strange. Skip forward 8m:05s on following video.

http://www.youtube.com/watch?v=sgdTnBU0_N0

No idea :-|


Ah, I think that youtube fellow is not a million miles away from here...

Nice work :-)

--
Adrian C

Hi!

Where on the AC wiring board?

It wouldn't matter so far as I can tell, the line cord is *not*
polarized. So it could be either one, depending upon which way the
plug is inserted into the outlet.

There is no third grounding pin.

You've never looked then...

Oh, really?

William

Hi!

Nice work :-)

Good job. :-) If I had a prize, you'd win it.

I would not dare to call myself an expert, but I think it is important
to do what I can to point out that things can usually be fixed instead
of just thrown away. I'm definitely learning...

William

Hi!

Got schematic?

I have the complete service manual for the unit. However, it doesn't
seem to show any connection between speaker - and the AC line.

That's not to say it isn't there. I have yet to spend a lot of time
looking at it, as right now I'm dealing with a bat that is somehow in
the wall of my house.

William

"William R. Walsh"


That's not to say it isn't there. I have yet to spend a lot of time
looking at it, as right now I'm dealing with a bat that is somehow in
the wall of my house.


** You sure that is where the bat is ??

Not in the belfry ???




.... Phil

That's not to say it isn't there. I have yet to spend a lot
of time looking at it, as right now I'm dealing with a bat
that is somehow in the wall of my house.

There's no need to kill it. Simply leave all the doors and windows open at
night (if possible), and it will likely find its way out, hopefully before
biting everyone in your family and infecting them with incurable rabies that
will cause them to die in unspeakable agony.

Hi!

There's no need to kill it.

I'd prefer not to kill the poor thing if I can help it.

The trick is to find out where it got in, because this is the second
one. (The first either came out or died in a different wall. I think
it got out, as I never smelled anything bad.)

infecting them with incurable rabies that will cause them to
die in unspeakable agony.

It's just a grin-a-minute around here, isn't it?

William

"William R. Walsh" wrote in message
...
Hi!

There's no need to kill it.

I'd prefer not to kill the poor thing if I can help it.

The trick is to find out where it got in, because this is the second
one. (The first either came out or died in a different wall. I think
it got out, as I never smelled anything bad.)

infecting them with incurable rabies that will cause them to
die in unspeakable agony.

It's just a grin-a-minute around here, isn't it?

William

Best not kill it. I've just - 10 minutes ago - finished reading an article
in my Sunday newspaper, about a mystery disease that is sweeping through the
bat population of North America, and decimating whole colonies. They think
that it might not be a disease as such, but a fungal infection which leaves
a white deposit on the noses of the bats. Apparently, bats are responsible
for consuming millions of tons of insects which do harm, and if the bat
situation becomes serious enough in terms of loss of numbers, it could have
a devastating effect on the balance of the ecosystem.

Back to the resistor question. Such resistors, mostly with no immediately
discernable purpose, are often to be found strung around the insides of
amplifiers and hifis. You sometimes find things like a metal bracket that
for whatever reason, the manufacturers didn't want hard grounded, connected
to hard ground via such a resistor. Could it be something like this, and the
connection point on the speaker connector board, was just a physically
convenient point to hook it to ?

As to finding it on the schematic, it might well not be shown where you
expect it to be. I have seen these resistors shown as a completely isolated
entity, within dotted lines, hidden up a corner of the diagram somewhere.
You might find it shown on the layout diagrams, or the internal wiring
diagram or block diagram though.

Arfa

There's no need to kill it.

I'd prefer not to kill the poor thing if I can help it.
The trick is to find out where it got in, because this is the second
one. (The first either came out or died in a different wall. I think
it got out, as I never smelled anything bad.)

infecting them with incurable rabies that will cause them to
die in unspeakable agony.

It's just a grin-a-minute around here, isn't it?

Actually, I adore bats, but couldn't resist the temptation to play on
people's prejudices.

Bats will die fairly quickly if they don't have food, so you want to get the
little critter outta there promptly. In theory, opening up everything might
work, as the bat might have come in tru de window.


Best not kill it. I've just - 10 minutes ago - finished reading an article
in my Sunday newspaper, about a mystery disease that is sweeping through
the
bat population of North America, and decimating whole colonies. They think
that it might not be a disease as such, but a fungal infection which
leaves
a white deposit on the noses of the bats. Apparently, bats are responsible
for consuming millions of tons of insects which do harm, and if the bat
situation becomes serious enough in terms of loss of numbers, it could
have
a devastating effect on the balance of the ecosystem.

People have been aware of this problem for decades. Though bats do have a
higher percentage of rabies than other mammals, it hardly ever transferred
to humans unless they touch a sick animals.

Bats are our friends. They kill tons and tons of inset pests. Love 'em.

On Mon, 24 May 2010 07:39:49 -0700, William Sommerwerck wrote:

That's not to say it isn't there. I have yet to spend a lot of time
looking at it, as right now I'm dealing with a bat that is somehow in
the wall of my house.

There's no need to kill it. Simply leave all the doors and windows open
at night (if possible), and it will likely find its way out, hopefully
before biting everyone in your family and infecting them with incurable
rabies that will cause them to die in unspeakable agony.

You can always rent a Batman costume and see if it will follow you out
the door.

On Mon, 24 May 2010 16:47:19 +0100, Arfa Daily wrote:

Best not kill it. I've just - 10 minutes ago - finished reading an
article in my Sunday newspaper, about a mystery disease that is sweeping
through the bat population of North America, and decimating whole
colonies. They think that it might not be a disease as such, but a
fungal infection which leaves a white deposit on the noses of the bats.

Damn, the bats have found out about Cocaine!

"William Sommerwerck" wrote in message
...
There's no need to kill it.

I'd prefer not to kill the poor thing if I can help it.
The trick is to find out where it got in, because this is the second
one. (The first either came out or died in a different wall. I think
it got out, as I never smelled anything bad.)

infecting them with incurable rabies that will cause them to
die in unspeakable agony.

It's just a grin-a-minute around here, isn't it?

Actually, I adore bats, but couldn't resist the temptation to play on
people's prejudices.

Bats will die fairly quickly if they don't have food, so you want to get
the
little critter outta there promptly. In theory, opening up everything
might
work, as the bat might have come in tru de window.


Best not kill it. I've just - 10 minutes ago - finished reading an
article
in my Sunday newspaper, about a mystery disease that is sweeping through
the
bat population of North America, and decimating whole colonies. They
think
that it might not be a disease as such, but a fungal infection which
leaves
a white deposit on the noses of the bats. Apparently, bats are
responsible
for consuming millions of tons of insects which do harm, and if the bat
situation becomes serious enough in terms of loss of numbers, it could
have
a devastating effect on the balance of the ecosystem.

People have been aware of this problem for decades. Though bats do have a
higher percentage of rabies than other mammals, it hardly ever transferred
to humans unless they touch a sick animals.

Bats are our friends. They kill tons and tons of inset pests. Love 'em.



According to this article, the current white nose problem, is a new one, not
a decades old one. The same fungus has also been found on bats in Europe,
but it doesn't appear to kill them, so they are thinking that maybe the
problem has existed over here before, and the bat population is immune to
the effects. They think that the white powder acts as an irritant, and keeps
waking the bats during their hibernation period, and that this results in
premature useage of the fat deposits that they have built up to see them
through, and thus, they die of starvation.

Arfa

"Meat Plow" wrote in message
news
On Mon, 24 May 2010 16:47:19 +0100, Arfa Daily wrote:

Best not kill it. I've just - 10 minutes ago - finished reading an
article in my Sunday newspaper, about a mystery disease that is sweeping
through the bat population of North America, and decimating whole
colonies. They think that it might not be a disease as such, but a
fungal infection which leaves a white deposit on the noses of the bats.

Damn, the bats have found out about Cocaine!


LOL !!

Arfa

On Mon, 24 May 2010 07:33:52 -0700 (PDT), "William R. Walsh"
wrote:

Hi!

Nice work :-)

Good job. :-) If I had a prize, you'd win it.

I would not dare to call myself an expert, but I think it is important
to do what I can to point out that things can usually be fixed instead
of just thrown away. I'm definitely learning...

William

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static
voltage that could build up in the circuit. That would probably happen
if you were connecting a speaker up, and you were charged up (could be
anywhere from a few volts to tens of thousands of volts). Walking on a
nylon carpet in a dry house (less than 20% humidity) can generate
enough static electicity to jump a gap of more than a centimeter. In
northern Canada during winter, I've generated 2-3cm sparks this way.
The DC voltage or the transient current may stress or damage
components.
Touching the case or metal knobs of your amp when you are charged,
may also stress components in your amp, especially if the case isn't
grounded (has a 2-wire cord).
The resistor allows for a discharge path to the AC line, so that an
excessive high voltage is not impressed across the insulation between
primary and secondary of the power transformer/switcher. The
interwinding capacitance also allows transient current flow, that
reduces the instantaneous voltage difference between primary and
secondary. Without the wierd little component, your power
transformer/switcher would have to withstand up to 10-50kv. That's
$$$$$! Typical transformers are rated 2-4kv.
The DC currents that are generated while you build up a charge
(scuffing your feet across a rug) are quite small, in the nano- or
micro-amp range. However, once you are charged (humans have about
150-300pf self capacitance) to many kilovolts, you can make a fairly
nasty zap. If I remember correctly, the human body model for
eltrostatic discharge has about 1500 ohms effectively in series with a
few hundred picofarads. For testing equipment, that capacitance is
charged to 3-5 kv. The transient current is quite significant! The
risetime is quite small, and transient currents can induce voltages in
places you wouldn't expect.
Sometimes you also find a ceramic capacitor in addition to (or often
instead) of the resistor. I've seen values of around .001uf, rated at
several kv. Be very careful replacing these components.... should that
capacitor or resistor fail, you could die. You should be very
concerned about the reliability of these parts.
When you discharge a current into the electronic circuit (it
ultimately heads for ground) you create a circuit between your body
capacitance (200pf), body series resistance (1500 ohms), and the power
transformer insulation in parallel with the protective
resistor/capacitor. You can calculate the voltages applied to the
power transformer or switcher if you know winding and stray
capacitances.
Colour TV's and monitors are a problem, since you can get
discharges off the front of the screen. That introduces a similiar
current to ground that must be dealt with. Switched power supplies
will have similiar issues plus dealing with protecting their control
circuits.
Of course the "protective" resistor or capacitor is chosen to limit
the "leakage current", should you touch the unit and be at ground
potential. That current depends on your electrical code.... values are
from a few microamps to a few hundred microamps. For me, I can sense
tens of microamps, and it starts to tingle around half of a milliamp
(AC 60Hz). I can't feel DC until quite a few ma., then I sense it as a
muscle pulling.
The protective resistor/capacitor is to both save your amp from you,
and you from your amp. It protects you in case you over-stressed some
part because of your charge, and that overstressed part breaks down
and applies AC to the circuit and you. It protects your wallet from
other non-lethal circuit failures. It appears to give you some risk in
the form of a small leakage current.
If you doubt the component, measure the AC current (not voltage)
between amp and ground, for both polarities of the plug (if you have a
choice of polarity). Put a resistor (say about 10kohm) in series with
your meter so you don't blow your meter up should the case or amp
circuit be live to ground. Any current greater than a few hundred
microamps, and I'd retire your amp.

Paul G.

"Paul G."

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static
voltage that could build up in the circuit.

** Correct.

That would probably happen
if you were connecting a speaker up, and you were charged up (could be
anywhere from a few volts to tens of thousands of volts). Walking on a
nylon carpet in a dry house (less than 20% humidity) can generate
enough static electicity to jump a gap of more than a centimeter. In
northern Canada during winter, I've generated 2-3cm sparks this way.
The DC voltage or the transient current may stress or damage
components.

** Note that the unit is a * receiver * therefore it has antenna sockets
on the back.

A rooftop mounted antenna can acquire very high DC voltages on a dry, windy
day - more then 10kV.

The PROBLEM is with the insulation of the transformer in the PSU of the
receiver - the primary side is linked to the AC supply so does no "float"
up with the rest of the unit when the antenna becomes charged.

If no leakage path exists to drain away the charge generated by wind on the
antenna, the resulting 10kV plus voltage difference will stress the
insulation in the AC tranny until is flashes over inside, making a small
spark and associated EMI which may be audible during FM or AM reception.

More importantly however, repeated sparking will cause the AC transformer's
insulation to eventually fail and the whole unit becomes live !!!

A resistor of about 4.7 Mohms to 10 Mohms is sufficient to keep DC voltage
build up on the antenna connection within safe limits and poses no shock
hazard to uses despite one end connecting to the live AC conductor.

BTW:

Such resistors are of a special high voltage type approved for this purpose
and should never be replaced with general purpose ones.


..... Phil

On Tue, 25 May 2010 13:01:09 +1000, "Phil Allison"
wrote:

......[snip!]......

BTW:

Such resistors are of a special high voltage type approved for this purpose
and should never be replaced with general purpose ones.


.... Phil




To further Phil's point, I used to work at RCA at a television
manufacturing plant back in the '60's. In the previous 10 years from
that, a number of sets (not sure if they were RCA brand or not) had
used ordinary paper capacitors wired to the AC line. They were wax
impregnated. These were installed on the "instant-on" TV's. Instant-on
meant that the unit had power applied to part of the circuitry even
though the unit was seemingly turned off. When you turned the unit on,
most of the tubes were already hot, and the unit came on in a few
secs, instead of about half a minute. Well, some of those capacitors
failed, they overheated, and caught fire (wax burns real good), the TV
cabinet (wood/plastic), caught fire, the house caught fire, and
everyone was in bed, assuming the TV was really off.
A number of families perished.
The immediate engineering fix was to have the same wretched
capacitors enclosed in a little porcelain tube, with fire resistant
cement covering up the ends. I still have one or two in my junkbox. A
few years later they used plastic film capacitors, whose dielectric
would not burn as easily. Nowadays there are very stringent standards
that must be applied for components that are attached to the
powerline, or are in circuits where the energy is not limited to safe
values.
I always get the heebie-jeebies making up electronic units that run
off the powerline. Some are designed for hospital/medical use. So many
standards, so many things to go wrong, so many potential disasters.
That's why I feel much more secure buying approved and certified power
supplies that I can run my circuitry from.
Don't screw around with the circuitry and wiring attached to the
powerline!

Paul G.

On May 24, 7:35*am, "William R. Walsh" wrote:
Hi!

Got schematic?

I have the complete service manual for the unit. However, it
doesn't
seem to show any connection between speaker - and the AC line.

That's not to say it isn't there. I have yet to spend a lot of time
looking at it, as right now I'm dealing with a bat that is somehow
in
the wall of my house.

William

Are you sure of that? I just looked at the schematic of my Technics
SA-160 receiver and there it is. R791 3.3Meg 1/2 Watt from the neutral
side of the power input to ground (polarized power plug). This _may_
happen physically near the speaker terminals simply because the power
and speaker switches are grouped together. On the schematic it's shown
on the primary side of the power transformer, not at the speaker
connections.

G²

On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote:

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static

And Paul G wins the contest!

Go claim your prize, a date with Phil Allison.

The resistor is there to protect the amplifier from static discharge.
Said static could build up while wiring up the speakers or even after
they are wired scooting them around on the carpet.

Hi!

*Probably a guess

It's as good as anything to me. It certainly does not show up in the
schematic, nor the parts list.

Its purpose is for "leaking" any DC static voltage that could
build up in the circuit. That would probably happen
if you were connecting a speaker up, and you were charged up
(could be anywhere from a few volts to tens of thousands of
volts).

So that's got me thinking...

Perhaps this serves to protect the hybrid module from such things?
It's my belief that the hybrid power amplifier is already something of
a delicate part.

I've noticed already that this receiver also contains additional relay/
outboard circuit protection against failure of the hybrid possibly
putting a power supply rail on a speaker. Earlier and other models did
not do that, instead relying on ineffective protection measures built
into the hybrid module.

Maybe the Technics/Panasonic engineers were trying to improve the
reliability of their design? I've seen a lot of these receivers that
were dead, usually as a result of hybrid module failure.

Touching the case or metal knobs of your amp when you
are charged, may also stress components in your amp, especially
if the case isn't grounded (has a 2-wire cord).

It's not...there is only a two wire, non-polarized cord set.

Be very careful replacing these components.... should that
capacitor or resistor fail, you could die. You should be very
concerned about the reliability of these parts.

I don't have any reason to believe the resistor itself is bad. The
front of the receiver and all of its controls are plastic.

That current depends on your electrical code.... values are
from a few microamps to a few hundred microamps.

The service manual for the set explains tests that can be run to
determine if the leakage is within specification. It would definitely
appear to be well within specifications.

As with you, I can usually feel a tingle from even very low current
leakage sources. I much prefer using test equipment to resolve any
uncertainty, anything else could result in a nasty surprise at the
least. I have not noticed anything from this set, and have no reason
to believe there is any problem.

Any current greater than a few hundred microamps, and I'd
retire your amp.

Fortunately, I do not think that this will be a problem. The unit
seems to operate safely in every regard. If anything, I will probably
be replacing the main filter capacitors as a precautionary measure.
The power supply section of this receiver runs hot and the original
filters are ~23 years old. They work fine now, but I do not want a
problem.

William

In article , Meat Plow wrote:
On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote:

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static

And Paul G wins the contest!

Go claim your prize, a date with Phil Allison.

The resistor is there to protect the amplifier from static discharge.
Said static could build up while wiring up the speakers or even after
they are wired scooting them around on the carpet.

I think I have added resistors like that to my circuits. It can help but is not
foolproof. A static charge to the amplifier metal will occur
regardless of resistance to AC ground. It can help prevent transformer
arcover.

greg

On Tue, 25 May 2010 15:05:59 +0000, GregS wrote:

In article , Meat Plow
wrote:
On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote:

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static

And Paul G wins the contest!

Go claim your prize, a date with Phil Allison.

The resistor is there to protect the amplifier from static discharge.
Said static could build up while wiring up the speakers or even after
they are wired scooting them around on the carpet.

I think I have added resistors like that to my circuits. It can help but
is not foolproof. A static charge to the amplifier metal will occur
regardless of resistance to AC ground. It can help prevent transformer
arcover.

greg

Nothing is foolproof. My reference was strictly static discharge via
speaker wires. Since the resistor is not in the schematic from what I
understand, it must be a factory fitting after a trend was spotted in
warranty repairs. Maybe the output device is sensitive to ESD augmented
by the output circuit design.

On Tue, 25 May 2010 07:33:01 -0700 (PDT), "William R. Walsh"
wrote:

.......[snip!}.........

So that's got me thinking...

Perhaps this serves to protect the hybrid module from such things?
It's my belief that the hybrid power amplifier is already something of
a delicate part.

I've noticed already that this receiver also contains additional relay/
outboard circuit protection against failure of the hybrid possibly
putting a power supply rail on a speaker. Earlier and other models did
not do that, instead relying on ineffective protection measures built
into the hybrid module.

Maybe the Technics/Panasonic engineers were trying to improve the
reliability of their design? I've seen a lot of these receivers that
were dead, usually as a result of hybrid module failure.


Although I repaired a number of amps with discrete and module
outputs, I don't have enough experience to say which are worse. The
early discrete circuits were pretty vulnerable.... I don't remember
any customers that that suggested electrostatic discharge as a cause
for the amp's failure. Usually it was power on/off, or load abuse
(shorting speakers, disconnecting while at full volume, etc.).
I believe that ESD (electrostatic discharge) into the speaker line
is not likely to bother the output circuit. The output devices are
designed to withstand short bursts of current, usually in excess of
10-20 amps. The half microsecond or so 2-3 amp transient generated by
the human ESD model is not likely to bother the output devices, since
there is sufficient capacitance in the devices themselves and the
associated circuitry to absorb significant charge. The output circuit
is not likely to be in a high impedance state. The tiny DC current
generated by scuffing across a rug, even though driven by a very high
voltage would not affect the module, unless the module circuitry was
in excess of hundreds or thousands of megohms. The components that are
likely to suffer from static voltages are the power supply where it
isolates the input AC line. The thousands of megohms insulation will
build up a high voltage as the static current tries to get to ground.
That's where the weird little resistor allows a path for the
current to seek ground. As has been stated earlier, if your amp has a
receiver in it, you can also get some very impressive static voltages
(driven by very tiny currents) from external antennae .

As you say, the newer amps have protection circuitry that senses
overcurrent, etc, and shuts off the output terminals. I remember
looking at the schematic of a cheapy 5.1 ch. Yamaha amplifier - it
monitored about 10-15 voltages and currents, and the microcontroller
would only energize the output if all the parameters were in the
correct range. There were hybrid modules throughout this amp. I
suspect the paranoia was not so much for the amp, but to protect the
customers speakers. (There is a very negative reputation for an amp
that blows a customers speaker!) I was quite impressed with the degree
protection and control of this amp... you could even run diagnostic
routines on it to check its performance, yet its price was around
$200. The fault I found was someone hadn't tightened the screw that
held one of the output modules to the heatsink, and its overheating
would shutdown the amp at high output levels.

......[snip !].........

Fortunately, I do not think that this will be a problem. The unit
seems to operate safely in every regard. If anything, I will probably
be replacing the main filter capacitors as a precautionary measure.
The power supply section of this receiver runs hot and the original
filters are ~23 years old. They work fine now, but I do not want a
problem.

William

The little electrolytics throughout the amp are just as likely to
fail as the main ones (maybe even more so), so if the main caps are
cool, and your amp doesn't have 120 Hz hum in it, why bother? I would
only do a total recap if the amp was something very exceptional. Your
chances of screwing something up doing a complete recap are quite
high.
If the thing dies badly, you can always go scrounging on "big
garbage pickup day" and get another Japanese amp that has been tossed
out and will probably remain useful for many more years.

Paul G.

In article , Meat Plow wrote:
On Tue, 25 May 2010 15:05:59 +0000, GregS wrote:

In article , Meat Plow
wrote:
On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote:

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static

And Paul G wins the contest!

Go claim your prize, a date with Phil Allison.

The resistor is there to protect the amplifier from static discharge.
Said static could build up while wiring up the speakers or even after
they are wired scooting them around on the carpet.

I think I have added resistors like that to my circuits. It can help but
is not foolproof. A static charge to the amplifier metal will occur
regardless of resistance to AC ground. It can help prevent transformer
arcover.

greg

Nothing is foolproof. My reference was strictly static discharge via
speaker wires. Since the resistor is not in the schematic from what I
understand, it must be a factory fitting after a trend was spotted in
warranty repairs. Maybe the output device is sensitive to ESD augmented
by the output circuit design.

I would go along with saying, it has nothing to do with output devices.
it will discharge a DC differential in the amps circuit vs AC ground. It
could do this and that, but could provide power off protection and transformer
arc protection. Pretty much guessing beyond this.
HV arc noise ? I had problems once with an 8 track capstan, had
to add a static drain wire.

greg

Hi!

Although I repaired a number of amps with discrete and module
outputs, I don't have enough experience to say which are
worse.

I don't know how much experience it takes, probably more than I have.
In any case, the majority of burnt amps/receivers that I've seen were
hybrid-based. I've also heard others talk badly of the hybrids in
terms of reliability.

*As you say, the newer amps have protection circuitry that senses
overcurrent, etc, and shuts off the output terminals. I remember
looking at the schematic of a cheapy 5.1 ch. Yamaha amplifier -
it monitored about 10-15 voltages and currents, and the
microcontroller would only energize the output if all the
parameters were in the correct range. There were hybrid modules
throughout this amp.

That does sound impressive. I haven't seen an amplifier with that much
protection in place, at least not yet. Of course, the work I do is
generally limited to stuff that I find in the trash or somewhere else
and don't feel that I can pass up. What I find is usually stuff that's
a few or many years removed from the current state of the art.

I unintentionally tested the protection circuit in a Sherwood RX-4109
receiver the other day. I was moving a door and I snagged some speaker
wires, pulling them out of the speaker and shorting the wiring. Its
protection circuit worked exactly as intended. The sudden power off
startled me (to say the least) but there was no lasting harm. I
reconnected the wiring, moved it out of harm's way and turned the set
right back on.

I was quite impressed with the degree protection and control of
this amp... you could even run diagnostic routines on it to check
its performance, yet its price was around $200.

I credit the ever-falling price of microcontrollers for this sort of
thing. (There was an interesting article about that on the Dan's Data
web site recently.)

The little electrolytics throughout the amp are just as likely to
fail as the main ones (maybe even more so), so if the main caps
are cool, and your amp doesn't have 120 Hz hum in it, why
bother?

Maybe as a pre-emptive strike? It had been my understanding that
electrolytic capacitors operating in less than wonderful conditions
were more likely to fail than those running in a cooler location or
under less electrical stress.

Here's the thing...I had wanted to find one of these little Technics
receivers for a long time. The trouble is, every one I could put my
hands on had been badly mistreated, blown up or both. I spent years
looking without any luck.

I'm not going to even try to justify my desire to have one. I just
wanted one in nice working condition and that's that. Something about
the overall design appealed to me.

When I saw this one sitting at a public television and radio
fundraiser sale, I just had to have it once I saw that it was
described as "working". I didn't even argue much over the price. Now
that I've got one in good working order, I guess you could say that
I'm just a little...protective (?) ... of it. (Yes, I realize how that
may sound dumb. It is, after all, just a "thing".)

William

On Tue, 25 May 2010 16:17:18 +0000, GregS wrote:

In article , Meat Plow
wrote:
On Tue, 25 May 2010 15:05:59 +0000, GregS wrote:

In article , Meat Plow
wrote:
On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote:

Probably a guess, but I suspect the mystery part is a high value
resistor as Phil stated. Its purpose is for "leaking" any DC static

And Paul G wins the contest!

Go claim your prize, a date with Phil Allison.

The resistor is there to protect the amplifier from static discharge.
Said static could build up while wiring up the speakers or even after
they are wired scooting them around on the carpet.

I think I have added resistors like that to my circuits. It can help
but is not foolproof. A static charge to the amplifier metal will
occur regardless of resistance to AC ground. It can help prevent
transformer arcover.

greg

Nothing is foolproof. My reference was strictly static discharge via
speaker wires. Since the resistor is not in the schematic from what I
understand, it must be a factory fitting after a trend was spotted in
warranty repairs. Maybe the output device is sensitive to ESD augmented
by the output circuit design.

I would go along with saying, it has nothing to do with output devices.
it will discharge a DC differential in the amps circuit vs AC ground. It
could do this and that, but could provide power off protection and
transformer arc protection. Pretty much guessing beyond this. HV arc
noise ? I had problems once with an 8 track capstan, had to add a static
drain wire.


Could serve dual purpose. Guessing is good, stimulates the mind. I could
go along with the arc noise. Snapping while it was on with a good jolt
could cause speaker protection to kick in or pop a midrange or tweeter.

On Tue, 25 May 2010 09:31:40 -0700 (PDT), "William R. Walsh"
wrote:

.....[ snip! ]......

Here's the thing...I had wanted to find one of these little Technics
receivers for a long time. The trouble is, every one I could put my
hands on had been badly mistreated, blown up or both. I spent years
looking without any luck.

I'm not going to even try to justify my desire to have one. I just
wanted one in nice working condition and that's that. Something about
the overall design appealed to me.

When I saw this one sitting at a public television and radio
fundraiser sale, I just had to have it once I saw that it was
described as "working". I didn't even argue much over the price. Now
that I've got one in good working order, I guess you could say that
I'm just a little...protective (?) ... of it. (Yes, I realize how that
may sound dumb. It is, after all, just a "thing".)

That's funny.... when I was visiting my daughter in Ottawa, I
spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed
a Techics (!) "new class A" amp, and a Technics CD player, and
stuffed them in the trunk of the car for the 1200 mile return trip. My
wife was really ****ed about the lack of space in the trunk, but hey,
the stuff was free. The CD player worked just fine (still does), and
the amp worked OK, but had a noisy cooling fan. I put a much quieter
fan in it, and redesigned the air cooling flow, and modified the
circuitry to give it proportional control of the fan. Works great....
you have to have your head right against the amp to hear it.
I find it depressing to see the stuff that gets tossed out. Around
here (Nova Scotia) you can't throw electronics stuff out, it has to go
to a special recycler. Now you can't get your hands on old electronic
throw-aways, the recycler refuses to let anyone have any of the stuff
so you can repair it (and do the ultimate recycling where you bring it
back to life).

I have had electronic equipment that I've tried to preserve and
gone to extraordinary lengths to keep them running, even though I KNOW
it's not worth the effort. It's like you want to cheat the grim reaper
of electronics. You kinda wish someone would do the same for you.....

Paul G.

On 5/25/2010 4:39 PM Paul G. spake thus:

That's funny.... when I was visiting my daughter in Ottawa, I
spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed
a Techics (!) "new class A" amp, and a Technics CD player, and
stuffed them in the trunk of the car for the 1200 mile return trip.

Hey, my current amp is one a'them Technics "new class A"s, a SU-V6X.
What's yours? Got mine really cheap years ago at a Starvation Army store.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

On Tue, 25 May 2010 18:49:19 -0700, David Nebenzahl
wrote:

On 5/25/2010 4:39 PM Paul G. spake thus:

That's funny.... when I was visiting my daughter in Ottawa, I
spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed
a Techics (!) "new class A" amp, and a Technics CD player, and
stuffed them in the trunk of the car for the 1200 mile return trip.

Hey, my current amp is one a'them Technics "new class A"s, a SU-V6X.
What's yours? Got mine really cheap years ago at a Starvation Army store.

Mine's a SU-V7B. I imagine there's not a lot of difference... I used
the schematics for SU-V98 to change some of the circuitry. That was
the only close schematic I could find on the internet. It wasn't quite
the same, but the reference designators (like R520, C123) were good
enough to locate things.
The original fan was irritatingly loud... I can't imagine how
anyone could put up with it.
It uses a hybrid module to drive the output, and I imagine only
much earlier models would use discrete transistors. I found it to be a
surprisingly powerful amp for class A, but their "new Clas A" just
slides the biasing up and down so that at low power it's still class A
but biased low enough to stay cool. There is an art to doing that, and
keeping the system well behaved and linear. I imagine there could be
problems if the amp is biased for quiet music, and a sudden loud
passage comes along that requires fast changing the operating point.
There are probably a good number of patents that relate to that bias
circuitry.
I've had no complaints about it, except for having to replace the
on-off switch (a low power switch that controls a relay which switches
the AC line). Because of the weird shape of the switch, and it being
alternate action, I had to jury-rig a small toggle switch with an
extension on its handle.
I used ductape to channel the air flow over the heatsink, to
improve the cooling. Running full output, the heatsink doesn't get
overly hot, and the exhaust air is quite warm. The fan I used was a
12v small quiet fan, similiar to those used on smaller CPU's.
Typical for much electronics, it's the mechanical stuff that seems
to fail first, or isn't properly designed to last.

Paul G.

On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh"
m put finger to
keyboard and composed:

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and repairing
the protection relay, I noticed that there is a wire coming from the
printboard that holds both the AC power input and accessory outlet
connections going to the "speaker -" connector for the "B" speaker
terminals.

There is a resistor inline with the wire coming from the AC wiring board.

That gives me an idea for testing subwoofers ...

Connect each speaker terminal to the active and neutral of a mains
supply. The frequency is not critical -- either 50Hz or 60Hz is fine.
A sinusoidal 240VAC source would be preferred, but 120VAC will do,
too.

If you damage your speaker, don't be discouraged. In fact you may need
to test quite a few units before you have weeded out all the inferior
ones, especially those used in car audio.

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

On 5/25/2010 9:25 PM Franc Zabkar spake thus:

On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh"
m put finger to
keyboard and composed:

I have a Technics SA-929 stereo receiver that is in good working
order. However, when I was inside it replacing a burnt out light
bulb and repairing the protection relay, I noticed that there is a
wire coming from the printboard that holds both the AC power input
and accessory outlet connections going to the "speaker -" connector
for the "B" speaker terminals.

There is a resistor inline with the wire coming from the AC wiring
board.

That gives me an idea for testing subwoofers ...

Connect each speaker terminal to the active and neutral of a mains
supply. The frequency is not critical -- either 50Hz or 60Hz is fine.
A sinusoidal 240VAC source would be preferred, but 120VAC will do,
too.

If you damage your speaker, don't be discouraged. In fact you may need
to test quite a few units before you have weeded out all the inferior
ones, especially those used in car audio.

Thank you. I love that! Maybe I can convince my homies around here to
implement this new testing methodology. We could set up a free testing
station on the main drag around here.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

On Wed, 26 May 2010 14:25:51 +1000, Franc Zabkar wrote:

On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh"
m put finger to
keyboard and composed:

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and
repairing the protection relay, I noticed that there is a wire coming
from the printboard that holds both the AC power input and accessory
outlet connections going to the "speaker -" connector for the "B"
speaker terminals.

There is a resistor inline with the wire coming from the AC wiring
board.

That gives me an idea for testing subwoofers ...

Connect each speaker terminal to the active and neutral of a mains
supply. The frequency is not critical -- either 50Hz or 60Hz is fine. A
sinusoidal 240VAC source would be preferred, but 120VAC will do, too.

If you damage your speaker, don't be discouraged. In fact you may need
to test quite a few units before you have weeded out all the inferior
ones, especially those used in car audio.

- Franc Zabkar

Cerwin Vega used to demonstrate one of their professional low frequency
audio drivers by plugging it into 120VAC line.

Hi!

That gives me an idea for testing subwoofers ...

Connect each speaker terminal to the active and neutral of a
mains supply.

Now come on, haven't you watched enough Youtube to know what happens
when you do that? ;-)

Interestingly, the very idea of connecting a speaker to the AC line is
mentioned early on in my copy of the ARRL's "Now You're Talking" book.
They tell you not to do so, and I suppose that there are some people
out there who need to be told that...more so because they'd hurt or
kill themselves in the process.

William

Hi!

The CD player worked just fine (still does), and the amp worked
OK, but had a noisy cooling fan. I put a much quieter
fan in it, and redesigned the air cooling flow, and modified the
circuitry to give it proportional control of the fan. Works great....

I have thought about doing something like that with this unit, as it
does get hot. I don't know if the circuit used is the "new class A" or
not. The receiver itself makes no mention of this feature, so I'd
guess not. There's not much room to add anything, at least not at a
point where I feel it would be close enough to help cool the power
supply as well. The last thing I would want to do is add a hum or
other annoying problem by way of design "improvements".

On the other hand, it has lasted over 20 years just the way it is. I
just don't like it when stuff runs that hot.

I find it depressing to see the stuff that gets tossed out.

As do I. Most recently I had to work hard to force myself not to pick
up a microwave oven. I didn't want or need it as a microwave--instead
I was hoping to harvest magnets, motors, control board and maybe the
case metal. Very little goes to waste around here.

Around here (Nova Scotia) you can't throw electronics stuff out,
it has to go to a special recycler. Now you can't get your hands
on old electronic throw-aways, the recycler refuses to let anyone
have any of the stuff so you can repair it (and do the ultimate
recycling where you bring it back to life).

I think they're afraid of liability or something along those lines. I
used to know a few recyclers, including one who would let me wander
all over the place, pick out what I wanted and pay him some small
price for it. Most of the others were at least somewhat receptive to
my rambling around when I told them that I knew to be careful and that
anything I took home with me was my problem--and the last that they
would hear of it. Most of what I picked up was computer equipment, and
the education I received was worth far more than the price I paid.

The same with junkyards...although I did not take anything home from
there because I certainly didn't have the space or time. I spent a lot
of time walking through those, looking at the things people had (for
whatever reason) cast away as junk. At least some of those cars would
have needed nothing more than a battery and some cleaning to be fine
once again. Heh...try doing that now. Most junkyards won't let you
anywhere nearby and the "old country junkyard" is a thing of the past
for the most part, taken away by tightening environmental regulations.

*I have had electronic equipment that I've tried to preserve and
gone to extraordinary lengths to keep them running, even
though I KNOW it's not worth the effort. It's like you want to cheat
the grim reaper of electronics.

Exactly. (Of course, there are also the devices that just seem to run
and run forever, with little to no maintenance whatsoever.)

You kinda wish someone would do the same for you..

Longevity does run in my family, so I might do alright there. The most
ready example is that of my grandfather, who at 96 does exactly as he
pleases.

William

On 5/25/2010 8:29 PM Paul G. spake thus:

On Tue, 25 May 2010 18:49:19 -0700, David Nebenzahl
wrote:

On 5/25/2010 4:39 PM Paul G. spake thus:

That's funny.... when I was visiting my daughter in Ottawa, I
spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed
a Techics (!) "new class A" amp, and a Technics CD player, and
stuffed them in the trunk of the car for the 1200 mile return trip.

Hey, my current amp is one a'them Technics "new class A"s, a
SU-V6X. What's yours? Got mine really cheap years ago at a
Starvation Army store.

Mine's a SU-V7B. I imagine there's not a lot of difference... I used
the schematics for SU-V98 to change some of the circuitry. That was
the only close schematic I could find on the internet. It wasn't quite
the same, but the reference designators (like R520, C123) were good
enough to locate things.
The original fan was irritatingly loud... I can't imagine how
anyone could put up with it.

Fan? What fan? Mine has no fan.

Yours must be a higher-powered unit than mine.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

On 5/26/2010 6:51 AM William R. Walsh spake thus:

[Franc Zabkar wrote:]

That gives me an idea for testing subwoofers ...

Connect each speaker terminal to the active and neutral of a
mains supply.

Now come on, haven't you watched enough Youtube to know what happens
when you do that? ;-)

I see nothing gets by you, William.

Now think about *why* Franc made this particular little joke. Ah, now
you're getting it.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)