Mystery component in Sam's PhotoFact

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.

"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 - - - - -

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.

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.

--
"Nowadays, security guys break the Mac every single day. Every single day,
they come out with a total exploit, your machine can be taken over totally.
I dare anybody to do that once a month on the Windows machine."
 -- Bill Gates, in an interview with Newsweek's Steven Levy

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

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

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

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.

Note: I'm trying to cross-post this to sci.electronics.repair, hope it works. If not, I'll try to post the info that's there, over to here.

Here's the physical description:

It's about 1/4" in diameter and 1/8" thick. The 2 leads are about

1/4" apart. The color is black with white charactors, which I next describe. It has a triangle laying on it's base (ie, pointing up). The corners of the triangle appear to have some detail, perhaps looking like arrowheads. I suspect it's the manufacturers logo which I think I've seen before, but I don't know which manufacturer. Below the triangle are the charactors "K271" and below that "99".

Looking thru this site, the logo looks like it's Matsushita/Panasonic.

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

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.

"Radiosrfun" wrote in news:45e0be7f$0$6837$ snipped-for-privacy@news.coretel.net:

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

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).

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.