Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old January 28th 08, 11:01 PM posted to sci.electronics.repair
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What is the purpose of the small neon bulb by the flyback on older TVs? (I haven't noticed it in any modern tvs.)
Someone asked me that the other day and I couldn't answer! Seems like I used to know (I'm an old-timer) but can't remember.
Thanks.

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Old January 28th 08, 11:56 PM posted to sci.electronics.repair
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"oldfogie" wrote in message
.. .
What is the purpose of the small neon bulb by the flyback on older TVs? (I
haven't noticed it in any modern tvs.)

A voltage clipper? Neon lamps have very high resistance and then drop to a
low resistance when the gas ionizes. About 60 volts, I think.


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Old January 28th 08, 11:59 PM posted to sci.electronics.repair
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oldfogie wrote:
What is the purpose of the small neon bulb by the flyback on older TVs? (I haven't noticed it in any modern tvs.)
Someone asked me that the other day and I couldn't answer! Seems like I used to know (I'm an old-timer) but can't remember.
Thanks.

50-100 volt spike clamp??
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Old January 29th 08, 12:26 AM posted to sci.electronics.repair
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Default Dumb TV question

oldfogie wrote:

What is the purpose of the small neon bulb by the flyback on older TVs? (I haven't noticed it in any modern tvs.)
Someone asked me that the other day and I couldn't answer! Seems like I used to know (I'm an old-timer) but can't remember.
Thanks.


Could be a voltage reference (~60 - 90 V), voltage drop or translation,
a hysteresis element in a multivibrator, clamp or even indicator of
some circuit's status.

Regards,

Michael
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Old January 29th 08, 12:28 AM posted to sci.electronics.repair
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Are you sure it is really a neon bulb? I'm thinking it is possibly a high
voltage spark gap which serves as overvoltage protection... Just my
thoughts. Without seeing it it would be hard to say for sure.

Bob

"oldfogie" wrote in message
.. .
What is the purpose of the small neon bulb by the flyback on older TVs? (I
haven't noticed it in any modern tvs.)
Someone asked me that the other day and I couldn't answer! Seems like I used
to know (I'm an old-timer) but can't remember.
Thanks.




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Old January 29th 08, 03:00 AM posted to sci.electronics.repair
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On Jan 28, 6:28�pm, "Bob Shuman" wrote:
Are you sure it is really a neon bulb? � I'm thinking it is possibly a high
voltage spark gap which serves as overvoltage protection... �Just my
thoughts. �Without seeing it it would be hard to say for sure.

� � Bob

"oldfogie" wrote in message

.. .
What is the purpose of the small neon bulb by the flyback on older TVs? (I
haven't noticed it in any modern tvs.)
Someone asked me that the other day and I couldn't answer! Seems like I used
to know (I'm an old-timer) but can't remember.
Thanks.


I'll bet it's a solid state GE from the early 1970s. They included the
bulb as a high-voltage indicator. This was to deter arcing with a
screwdriver as a test.
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Old January 29th 08, 03:15 AM posted to sci.electronics.repair
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Default Dumb TV question

Yes, I'm sure, was a small glass neon bulb soldered to chassis.
I looked through a good many old Sams folders, back into the '70s & '80s but never found a neon bulb in one. Problem is, just because it was near the fly doesn't have to mean it was in the fly circuit. So it must have been in some other circuit. I think it was for spike protection, for whatever circuit it was in.
I'm ready to just forget it, not important.
Thanks to all for replies!


"Bob Shuman" wrote in message ...
Are you sure it is really a neon bulb? I'm thinking it is possibly a high
voltage spark gap which serves as overvoltage protection... Just my
thoughts. Without seeing it it would be hard to say for sure.

Bob

"oldfogie" wrote in message
.. .
What is the purpose of the small neon bulb by the flyback on older TVs? (I
haven't noticed it in any modern tvs.)
Someone asked me that the other day and I couldn't answer! Seems like I used
to know (I'm an old-timer) but can't remember.
Thanks.


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Old January 29th 08, 05:44 AM posted to sci.electronics.repair
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Default Dumb TV question

A real neon bulb? I wish I owned a million of them, I love neon
lights/neon signs.I own an old broken neon NO VACANCY sign I bought at
the Goodwill store years ago.It was broken when I bought it.I like it
anyway.I think it dates back to the 1940s or 1950s.Nothing beats neon
lights and neon signs.
cuhulin

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Old January 29th 08, 06:02 AM posted to sci.electronics.repair
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I think it was used as a high-voltage clipper... sort of a high-voltage
zener diode. During normal operation it's never supposed to light up. I
often saw those on neck boards of old monochrome video monitors. Only once
did I ever see one light up and that was due to picture tube failure (the
precise details of which I can't remember now). The firing voltage of neon
bulbs is pretty high... at least 50 volts, some go as high as 90 volts.

BTW: If the bulb is placed across DC, only one of the interior electrodes
will light up. If the bulb is placed across AC, then both internal
electrodes will light up.




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Old January 29th 08, 02:46 PM posted to sci.electronics.repair
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Default Dumb TV question


"oldfogie" wrote in message
...
Yes, I'm sure, was a small glass neon bulb soldered to chassis.
I looked through a good many old Sams folders, back into the '70s & '80s
but never found a neon bulb in one. Problem is, just because it was near
the fly doesn't have to mean it was in the fly circuit. So it must have
been in some other circuit. I think it was for spike protection, for
whatever circuit it was in.
I'm ready to just forget it, not important.
Thanks to all for replies!




If it was a true neon bulb, then it wouldn't actually need to be connected
into any circuitry in order to light up as an indicator of flyback activity.
Most gas filled tubes will light in mid air if they are in close enough
proximity to a flyback tranny. Back when I was an apprentice, like 35 years
ago, the guy that I worked under in a TV workshop, used to keep a short thin
flourescent tube on his bench. He used this to test for horizontal output
stage activity, simply by waving it around the FB tranny. As I recall, he
used to reckon that he could tell a lot about how that stage was working,
when he had a lack of picture fault, just by the 'way' in which his little
tube lit up.

Most of the similar 'bulbs' that I've seen on CRT base connector boards,
have been gas-filled spark gaps. I seem to recall that they used to put
argon in them, and when they went off as a result of an inter-electrode
short in the tube, they lit up white, rather than the orange glow of a neon.

Arfa





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