Speaker - terminal connected to the AC line?

[William R. Walsh]

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

 

[Phil Allison]

"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

 

[PeterD]

On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh"
<newsgroups1@idontwantjunqueemail.walshcomptech.com> 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

 

[Adrian C]

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

 

[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

 

[Phil Allison]

"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

 

[William Sommerwerck]

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.

 

[Meat Plow]

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?

 

[Arfa Daily]

"William R. Walsh" <wm_walsh@hotmail.com> wrote in message
news:b280c1d8-d1d2-4b87-b7fb-40baa64cfa2a@o15g2000vbb.googlegroups.com...

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

 

[William Sommerwerck]

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.

 

[William R. Walsh]

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

 

[William R. Walsh]

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

 

[William R. Walsh]

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]

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

 

[Meat Plow]

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.

 

[Meat Plow]

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!

 

[Arfa Daily]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:hte9g6$udd$1@news.eternal-september.org...

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

 

[Arfa Daily]

"Meat Plow" <mhywatt@yahoo.com> wrote in message
newsan.2010.05.24.19.27.02@gmail.com...

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

 

[Paul G.]

On Mon, 24 May 2010 07:33:52 -0700 (PDT), "William R. Walsh"
<wm_walsh@hotmail.com> 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.

 

[Phil Allison]

"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