Old neon indicator light testing

Thread Starter

t kermi

Joined Oct 6, 2020
4
Hello,

Does someone have an idea how to test if an old small neon tube (cold cathode - I think) is working, please? My acquaintance bring it and the board with a relay to me to repair and I have no idea...

I mean what voltage range should I try to feed it and how to connect? I guess both ends to the voltage feed and the thin wire to the ground? Should AC or DC be preferred when testing?

Thanks!:)
 

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AlbertHall

Joined Jun 4, 2014
10,558
I agree on flash tube.
Was the thin wire wrapped around the tube?
If so it is the trigger wire and possibly the white box is a transformer to generate the trigger voltage.
 

Dodgydave

Joined Jun 22, 2012
9,666
That's a Xenon tube, the wire is wrapped around one end of the tube ,( where the silver paint ring is on the left), this is to fire the tube like a camera flash from a high DC voltage.
 

Thread Starter

t kermi

Joined Oct 6, 2020
4

Thread Starter

t kermi

Joined Oct 6, 2020
4
I agree on flash tube.
Was the thin wire wrapped around the tube?
If so it is the trigger wire and possibly the white box is a transformer to generate the trigger voltage.
Yes it was, there is a tinned contact on the tube that conducs to the internal metal strip. The thin wire was pressed against the contact by silicone rubber tube. I first thought that the box component was a cap, but it wasn't. And I got strange measurements thinking it was a relay... I will measure it again with low level AC.

I would otherwise visit the place where the machine is, but I have a chronic medical condition that is annoyingly limiting.

This part is from a car tire balancing mashine. And the owner just said that the light is supposed to light up when balancing. I thought he meant a constant output but this may be for some strobing instead.
 

Thread Starter

t kermi

Joined Oct 6, 2020
4
That's a Xenon tube, the wire is wrapped around one end of the tube ,( where the silver paint ring is on the left), this is to fire the tube like a camera flash from a high DC voltage.
Thanks for confirm. Then with DC that component might not be a transformer after all. But it's not a capacitor - I only got 40pF reading :)I will remove and measure it tomorrow.
 

bertus

Joined Apr 5, 2008
20,881
Hello,

It still could be a transformer.
I see a red and blue to the control and a brown one for the High voltage:

PSX_flash numbers.jpg


bristol flash color numbers.jpg

I have numbered your picture and put the numbers in the schematic


Bertus
 
The problem is not likely the xenon flash tube or trigger transformer on this board.
Note these are high voltage, you should measure around 340VDC across the tube ends and the trigger wire gets 4kV pulses but not measurable, you can hear the "click".

These car wheel balancers get banged around a lot, so the tire position switches go bad and then there is no trigger pulse to the strobe, once per tire rev. on the imbalanced side. I'd check those switches first, then the HV power and SCR.

If you must test the xenon flash tube and trigger transformer, a disposable camera flash board can provide the high voltage to test them.
 
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