Weird 1980s tv problem. Would like explanation.

[Chuck]

There was an AOC tv in the mid 80s that had capacitance touch switches
on the front and the channel indicators were illuminated with NE2 neon
bulbs. An ic drove transistor switches that turned the bulbs on and
off. The sets would come in where the channel couldn't be changed.
The first one took me a few hours to repair. The soluton was to
change the NE2 bulb on the channel the set was stuck on. The faulty
bulbs still lit at the proper voltage. Anyone have an idea how the
bulb could cause this fault? At the time we were a high volume repair
service so I didn't have the time to ponder circuit anomalies. Thanks.
Chuck

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[legg]

Neons emit random noise, dependent on individual breakdown
characteristics and current. At some amplitude level or frequency,
this could be overloading another section of the circuitry. This could
latch up a logic function in one state, if it resulted in positive
feedback.

You don't indicate if
....one channel was more problematic than others, in a wide range of
sets
... or whether it only occurred after some time period set on the
problematic channel
.... Cold or heat dependent
.....same sets returned more than once
etc.

Without a memory, either mechanical or electronic, this should have
been reset on recycling of power.

RL

[N_Cook]

And another weird neon problem. My main bench power supply, I've never
had to go inside it , so this minor problem remains.
The mains-on neon never lights in sunlight or room light but comes on
and flashes if its night time and next to no low light in the room, if
the ps is left switched on. Its a pip type, only a pip protrudes through
the casing if that is relevant.

[jurb...@gmail.com]

There were also Sonys like that. I thought it was leakage in the neon that caused that failure.

[pf...@aol.com]

This is an easy one... your vision is not linear based on lighting conditions, but very relative. A flash or low glow in a neon bulb would be entirely invisible under normal-light conditions, but in low light, your heightened sensitivity would pick it up easily. Further, Neon lamps, after they trigger, are not like many LEDs which are on/off devices. Once they trigger, voltage may drop considerably and they will still remain lit. So, if there is a capacitor in the circuit to trigger it, then when it reaches that point and 'fires' the lamp will flicker. But the carrier voltage to keep it running is not there. So it is only a flicker.

Some SS-relay operated neon ballasts from the very early days of electronic ballasts behaved the same way if wired with the 'neutral' switched, or at 277V under some conditions. Firing voltage is achieved, but operating voltage is not present. They flash. And if, as in some Euro applications, the "neutral" is above ground, this can be a real issue. The ballast design changed pretty quickly for this reason.

Peter Wieck
Melrose Park, PA

[pf...@aol.com]

On Monday, February 1, 2016 at 12:04:43 PM UTC-5, jurb...@gmail.com wrote:
> There were also Sonys like that. I thought it was leakage in the neon that caused that failure.

Yes, NE2 lamps age, and their internal resistance changes as a result. So, if the circuit depends on 'sensing' the operation of the neon lamp, and the operating resistance changes sufficiently, the circuit will latch.

Small pen-type one-point voltage sensors discern between AC & DC by only one side or the other glowing under DC, both under AC. Back in the day where mains DC was common (up to 2007 in NYC), that was important to know at a glance.

http://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/?_r=0

[MJC]

In article <a01e0a11-b02e-4c29...@googlegroups.com>,
pf...@aol.com says...

>
> Yes, NE2 lamps age, and their internal resistance changes as a result.

BTW What does the "2" signify?

Mike.

[Chuck]

On Tue, 2 Feb 2016 14:19:50 -0000, MJC <gra...@mjcoon.plus.com>
wrote:

It is a type of bulb number.

[Chuck]

It was channel independent, never intermittent and not hot or cold
dependent and the sets never returned for the same problem. By the
way Jur006 had the correct explanation. I had forgotten what it was
but his answer jarred my memory.

[Chuck]

On Mon, 1 Feb 2016 09:04:36 -0800 (PST), jurb...@gmail.com wrote:

>There were also Sonys like that. I thought it was leakage in the neon that caused that failure.

You are right. I had forgotten that was what caused the problem.
Thank you for jarring my memory.

[jurb...@gmail.com]

On Tuesday, February 2, 2016 at 9:43:21 AM UTC-5, Chuck wrote:

> On Mon, 1 Feb 2016 09:04:36 -0800 (PST), j...@gmail.com wrote:
>
> >There were also Sonys like that. I thought it was leakage in the neon that caused that failure.
>
> You are right. I had forgotten that was what caused the problem.
> Thank you for jarring my memory.
>
> ---
> This email has been checked for viruses by Avast antivirus software.
> https://www.avast.com/antivirus

I am replete with useless knowledge.

Next though, I don't even know if I ever even knew this, but what would that circuit be called in a digital IC. Like in a 74XX series or something ?

Something has to momentarily cut the current to all the other neons, likewise if you tried to make this in logic, it would most likely be a bunch of bistable flip flops but with a bit different gate arrangement.

Hell, I now wonder if neons is not maybe the best way to do it even today. There is only one main dropping resistor to all of them, when you hit the switch or whatever YOUR neon pulls more current and is fired, the other ones cannot fire because of not enough voltage.

There may be a nifty way of doing this with SCRs. I just can't think of an application right now. In fact I am pretty sure I could do it with SCRs and not too many other components. But then what ? Maybe some presets for equipment where things are still set by voltages ?

[Jon Elson]

jurb...@gmail.com wrote:


> There may be a nifty way of doing this with SCRs. I just can't think of an
> application right now. In fact I am pretty sure I could do it with SCRs
> and not too many other components. But then what ? Maybe some presets for
> equipment where things are still set by voltages ?

Actually, you could make the neon lamps, themselves, be the storage element.
Connect one side of all the lamps together, and tie to B+ with one resistor.
Have individual resistors to ground on each lamp. Short each individual
resistor with the select pushbutton. When you press this button, all other
neons will go out, and the selected one will light, and stay lit when you
release the button. Now, a circuit detects which of the individual
resistors has voltage across it, and selects the desired function.
Definitely cheap, and will work for a while. Eventually, the neons will get
far enough out of balance to cause problems.

Jon

[Chuck]

No It was a Large Scale CMOS chip. Maybe made by NEC. (NEC codes
worked with some AOC sets.)