Mystery component in Sam's PhotoFact

[j]

There's a schmatic symbol in Sam's PhotoFacts # 2908 and 2753-1
(covering JVC TV sets av-2749s, av-2759s, and av-2779s) that I don't
recall ever having seen before. It's NOT listed in the parts section
so I have no original or replacement numbers for reference. It's in
the grid (G1) circuit of the CRT.

Here's my attempt to describe it for those without access to the
PhotoFacts that I mentioned. It looks like a circle with a vertical
line running through the middle. On the upper left half of the circle
there's what appears to be a "black pie" section extending from a
point in the middle of the circle with an angle from about 11 to 12
o'clock. It almost touches the circumference. On the lower right half
of the circle there's a simular "black pie" section, with an angle
from about 5 to 6 o'clock. There's no line where the two "pie
sections" meet so it doesn't appear to be some sort of dual diode
device.

If anyone knows what it is, please let me know. I have researched
electronic schematic symbols on the web and in books but have not
found the symbol or what it represents.

 

[David]

There's a schmatic symbol in Sam's PhotoFacts # 2908 and 2753-1
(covering JVC TV sets av-2749s, av-2759s, and av-2779s) that I don't
recall ever having seen before. It's NOT listed in the parts section
so I have no original or replacement numbers for reference. It's in
the grid (G1) circuit of the CRT.

Here's my attempt to describe it for those without access to the
PhotoFacts that I mentioned. It looks like a circle with a vertical
line running through the middle. On the upper left half of the circle
there's what appears to be a "black pie" section extending from a
point in the middle of the circle with an angle from about 11 to 12
o'clock. It almost touches the circumference. On the lower right half
of the circle there's a simular "black pie" section, with an angle
from about 5 to 6 o'clock. There's no line where the two "pie
sections" meet so it doesn't appear to be some sort of dual diode
device.

If anyone knows what it is, please let me know. I have researched
electronic schematic symbols on the web and in books but have not
found the symbol or what it represents.

Spark gap. These are often part of the tube socket itself.

David

 

[j]

Spark gap. These are often part of the tube socket itself.

David

Thanks for replying. Have you worked on JVC TV's or have seen the
symbol before, or are you making an educated guess ?

The reason I ask is that there's no other such symbol on the other CRT
terminals in the schematic. I know in the past, Sam's has had two
arrows facing each other as the symbol for a spark gap. If you can
supply a reference book or web page, that would be great.

 

[Sofie]

"j"
You should trust David's reponse to your question..... likely a spark gap.
This is not just a JVC thing. Many brands and models use them andin
particular on the grids of the CRTs where HV potenetial can do lots of
component and circuitry damage upstream.
And, by the way, what is wrong with an educated guess anyway???
Daniel
- - - - -

 

[j]

You should trust David's reponse to your question..... likely a spark gap...

Thanks for responding. I apologize if my description was unclear but
sometimes it's hard to describe a graphics figure. Unfortunely, it's
very likely NOT a spark gap. I had not noticed before because it was
greyed out in the schematic, but all the CRT terminals have labeled
spark gaps (still two arrows facing each other - the arrows don't
touch).

Perhaps a circuit description would help. It starts with a 200 Volt
DC source connected to a 1 M ohm Resistor. A 10 uF cap is connected
in parallel with the R. The other side of the R is connected to the
anode of a 1N4007 diode, whose cathode is connected to ground.
Connected in parallel with the diode is the mystery component. Also
connected to the anode of the diode is a 1k ohm R, whose other side is
finally connected to the spark gap and grid of the CRT.

 

[Radiosrfun]

Thanks for responding. I apologize if my description was unclear but
sometimes it's hard to describe a graphics figure. Unfortunely, it's
very likely NOT a spark gap. I had not noticed before because it was
greyed out in the schematic, but all the CRT terminals have labeled
spark gaps (still two arrows facing each other - the arrows don't
touch).

Perhaps a circuit description would help. It starts with a 200 Volt
DC source connected to a 1 M ohm Resistor. A 10 uF cap is connected
in parallel with the R. The other side of the R is connected to the
anode of a 1N4007 diode, whose cathode is connected to ground.
Connected in parallel with the diode is the mystery component. Also
connected to the anode of the diode is a 1k ohm R, whose other side is
finally connected to the spark gap and grid of the CRT.

Why don't you post a picture of it in a binaries group - let the folks here
know WHERE - and then they can look at it and tell you? Then you won't be
confused as to how to describe it and they can see what the hell it is
you're trying to describe. Just take and scan the thing OR photograph it
with a arrow pointing to it.

 

[clifto]

Here's my attempt to describe it for those without access to the
PhotoFacts that I mentioned. It looks like a circle with a vertical
line running through the middle. On the upper left half of the circle
there's what appears to be a "black pie" section extending from a
point in the middle of the circle with an angle from about 11 to 12
o'clock. It almost touches the circumference. On the lower right half
of the circle there's a simular "black pie" section, with an angle
from about 5 to 6 o'clock. There's no line where the two "pie
sections" meet so it doesn't appear to be some sort of dual diode
device.

I've seen what you're talking about. I want to say it's a transient
protection device but I honestly don't remember it that well.

 

[David]

Thanks for replying. Have you worked on JVC TV's or have seen the
symbol before, or are you making an educated guess ?

The reason I ask is that there's no other such symbol on the other CRT
terminals in the schematic. I know in the past, Sam's has had two
arrows facing each other as the symbol for a spark gap. If you can
supply a reference book or web page, that would be great.

This is David. It was an educated guess.
Your circuit description makes it clear that the device is not directly
between the CRT grid and ground. This seems to be a strange circuit if in
fact the 200v supply has no signal component on it.
Have you visually looked at this mystery component? If so, what does it look
like?

David

 

[j]

This is David. It was an educated guess.
Your circuit description makes it clear that the device is not directly
between the CRT grid and ground. This seems to be a strange circuit if in
fact the 200v supply has no signal component on it.
Have you visually looked at this mystery component? If so, what does it look
like?

I agree, it does seem to be a strange circuit. I'll provide a
physical description next, but see my comments for clifto.

 

[j]

I've seen what you're talking about.

Do you remember what type or model number of the equipment had the
device ?

I want to say it's a transient
protection device but I honestly don't remember it that well.

Maybe I can jog your memory. This is from Herman's fourth edition of
Electronics for Electricians:

"(MOV) Metal Oxide Varistors are a type of thyristor that exhibit a
change of resistance with a change of voltage...the MOV is a bilateral
device... "

The problem is that the schmatic symbol for the MOV in the book and on
the web are the same but way different than what's on my Photofact
schematic.

Still, I'm leaning towards your suggestion. My wild guess from the
circuit description is that the purpose of the device is to protect
the diode and the CRT. The diode, in turn, protects the CRT by
limiting the voltage to 0.6 volts.

But I want to be sure. Perhaps by providing a physical description I
can get more info. I'll do that next.

 

[Bill Jeffrey]

Unlikely to be a transient suppressor, given its position in the circuit
you described. (I don't have a better idea, BTW!)

Actually, the whole circuit you described doesn't seem to make much
sense. Starting with 200 VDC (not VAC, right?), the power supply will
push 200 microamps at most through the 1 M resistor. If the whole 200 uA
passes through the diode, the 1N4007 (a rectifier diode) will be barely
in conduction, so the voltage developed across it will be perhaps 0.5
volts. If some of those microamps are shunted through the mystery
device, then the voltage will be even less.

And this small positive voltage is applied to the grid of the tube
through 1K, probably acting solely as an isolation resistor. I can't see
that there is enough voltage, or available fault current, at that
location, to warrant a transient suppressor. Hmm.

By the way, that grid isn't connected internally to some other element
in the tube, is it? I don't think you specified the tube type.

And the 200 volts is DC, not AC, right? In that case, I can't make any
sense of the 10 uF cap, either.

Sorry not to be of more help.

Bill Jeffrey

 

[Radiosrfun]

Unlikely to be a transient suppressor, given its position in the circuit
you described. (I don't have a better idea, BTW!)

Actually, the whole circuit you described doesn't seem to make much sense.
Starting with 200 VDC (not VAC, right?), the power supply will push 200
microamps at most through the 1 M resistor. If the whole 200 uA passes
through the diode, the 1N4007 (a rectifier diode) will be barely in
conduction, so the voltage developed across it will be perhaps 0.5 volts.
If some of those microamps are shunted through the mystery device, then
the voltage will be even less.

Again - why not post a scanned picture or digital picture of the part of the
schematic in question - with an arrow pointing to the part in question - in
the Binaries group so ALL can see it and know for SURE - what the hell it
is. I've seen guys offer suggestions and the OP seeming to refute each one
of them. At this rate, no one will ever know - including the one who needs
to know - the OP.

 

[Jim Land]

Again - why not post a scanned picture or digital picture of the part
of the schematic in question - with an arrow pointing to the part in
question - in the Binaries group so ALL can see it and know for SURE -
what the hell it is. I've seen guys offer suggestions and the OP
seeming to refute each one of them. At this rate, no one will ever
know - including the one who needs to know - the OP.

Yeah, what he said. Also, a closeup photo of the part in question.

 

[j]

Actually, "clifto" wrote that, but he was probably right (more on that
later).

Now, about the 200 VDC source, it also goes (thru a coil and resistor)
to the collectors of the 3 color output transistors. The video output
at the collectors goes (again thru a coil and r) to the respective
grids in the CRT. Apparently, transients are supposed to turn on the
diode, not the 200VDC. It still remains a strange circuit with the 10
uf cap in there.

After I added "sci.electronics.basic" to the group line in my posts
and posted the physical description of the mystery device, one of the
guys in sci.electronics.basic appears to have identified the device.
Knowing how to identifying a device from the charactors on the part is
sure helpful, but his messages have not appeared here.

Although it works like a Metal Oxide Varistor (MOV), Panasonic says
it's a Zinc oxide Nonlinear Resistor (ZNR).

http://panasonic.net/history/corporate/inp1968.html

Sam's PF did designate the component as "R364", but the symbol they
used led me to suspect that was an error. I haven't seen the symbol
on any recent or past schematics, only the 2 (1990-1991) in my
original post. I've already spent too much time and effort on this
apparently rare symbol so I won't post a pic in a binary group (I
don't know how anyways). If someone still wants to have an idea of
what the symbol looks like, a can give a different description but
that's all.