Neon based capacitor leakage tester

[ppppenguin]

In this post Mike Waatterson mentions his simple neon based capacitor leakage tester which can also test diode etc breakdown voltages without wrecking them.
https://golbornevintageradio.co.uk/forum...p?tid=7689&pid=87485#pid87485

Mike, it would be nice to give this its own thread, as it sounds like a very useful device.

[Mike Watterson]

Easy to make from a single use film camera that has flash!  I've obtained one from Tesco only a couple of years ago and they appear in Charity shops.

1) Make sure the flash works.  Some modern ones use an internal sealed in Alkaline AA cell.
2) Pop open the camera. You may need to peel off labels.
3) SAFETY: Danger Will Robinson!  Remove the battery. Note where the "fire" / shutter linkage presses. A membrane switch.
4) SAFETY: Danger Will Robinson! Make sure the typically 300uF main capacitor is discharged!
5) Remove the large 300V to 400V approx 200uF to 400uF electrolytic. It's not suitable for a regular PSU (ripple current exceeded). Note + and - connections.
6) Replace with a 630V polyester 0.5uF or 1uF.
7) Remove the Xenon tube.
8) Add 2 x 1M in series to the + Terminal. You need two rather than a single 2.2M to avoid breakdown.
9) Add any neon (they are still made, small ones are cheap) and a 630V 0.1 polyester or better cap across it in series with the - Terminal.
10) Fit power switch and a button or momentary toggle instead of the membrane switch which should peel off.

The Neon should light "solidly" if the safe end of the 2 x 1M resistors is applied to it. It will flicker more slowly with > 20 M Ohms. Add two terminals to your box for Device Under Test. Optionally add a third one to the - Terminal. Make sure the "live" end of the 2x 1M in series isn't exposed as 1uF and 300V is nasty!

You can put a uA meter/DMM in series to - Terminal or the neon with a part.
You can put a 20MΩ or higher input Z DMM on 750V range or 200V range etc to see the PIV of a diode or breakdown of a transistor (actually Avalanche Voltage) or unknown high voltage regulators, MOVs, Transorbs etc. It's non-destructive due to very low current.

I have one that uses a PP3 and one that uses 4 x AAA cells in a box with a 20uA meter (2x 1N4148 across the meter!). I think they may be from old flash guns, use Germanium and do about 600V rather than 300V. The PP3 driven one is in a small eddystone style box with a momentary toggle to power it, no "fire" button need. The battery lasts a very long time.

You can use 2 x short hooked leads and snip the "more live end" of a capacitor in a set and test. Larger value capacitor take longer to charge up, so neon will light, slow down and go out. Depending on application a cap that flashes once every 10 seconds may be OK. Modern caps, even 50V ceramic ones, don't have measurable leakage.
You can use it to roughly measure 22M to 1000M Ohm resistors.
Some old capacitor bridges had a tester like this, using the internal HT off the mains.

I think I may have done an article on the Radiomuseum.org some years ago.

It's no use for Electrolytics. I put them on the bench PSU and mA meter (DMM) in series, and wind up voltage slowly, I'll use the current limit at about 10mA if it needs reformed. Mostly even the 30V is enough to tell if a 150V to 500V old cap is faulty. I turn off the PSU and see how long it takes to discharge. Some PSUs don't like that, in such a case put 1M across cap (or a cheaper 1M DMM) and roughly time dropping volts after disconnecting from PSU. Only worth doing if Cap has reformed and less than 1mA. A cap can have no leakage because it's dried out and then it has high ESR and little capacitance.

Don't put a charged cap (from PSU or Flash gun based tester) into ANYTHING with out discharging it. Only old valve based bridges will survive that!

[Mike Watterson]

Here we are:
https://www.radiomuseum.org/forum/replac...rs.html#13

From 2011

A good simple test on mains sets with parallel valves, or a Series system where you use external HT, or the rectifier isn't part of the series heaters, or you stick a 1N4007 in the rectifier socket is to measure all the g1 pins and g2 pins with no valves fitted. The g2 pins should all be HT and the g1 pins all 0V, except in special cases. Or use a +90V test supply normally used by a battery valve radio.

The VRAT article is long gone.

[Mark Hennessy]

The VRAT article is long gone.

Actually, it's not "long gone". It's here:

https://www.radios-tv.co.uk/community/in...ge-tester/

As Chris says, claiming it's "long gone" is fake news.

Can I take this opportunity to remind GVR folks that we don't permit criticism of how other forums are run - please see Rule 4:

https://golbornevintageradio.co.uk/forum...ction=help&hid=8

I completely understand that some members have had issues with (or have been banned from) other forums, but that's between you and them, and nothing to do with GVR.

Mark

[ppppenguin]

Can you use an HT bench supply instead of a scrap camera? I know this means it's no longer a small portable unit but I have a 0-500V HT supply on my bench.

[Mike Watterson]

The VRAT article is long gone.

Actually, it's not "long gone". It's here:

https://www.radios-tv.co.uk/community/in...ge-tester/

As Chris says, claiming it's "long gone" is fake news.

Can I take this opportunity to remind GVR folks that we don't permit criticism of how other forums are run - please see Rule 4:

https://golbornevintageradio.co.uk/forum...ction=help&hid=8

I wasn't banned, I didn't rejoin. In fact it's a completely new site made with content from the old one, which was gone for ages. The original link IS gone, or in some fashion doesn't work. No particular criticism was made. The"link rot" is totally common. Wikipedia is full of it.

[Mike Watterson]

Can you use an HT bench supply instead of a scrap camera? I  know this means it's no longer a small portable unit but I have a 0-500V HT supply on my bench.

Sure you can use any sort of supply. Do be sure about the 2 x 1MΩ in series, without which it doesn't work and it's not safe. I'm not sure why you need to ask!

Though obviously larger capacitors are very dangerous once charged to 300V to 600V if they are passing the leakage test. An additional feature would be a two pole changeover power switch, where the second pole puts 10K or something across the capacitor.

[Mark Hennessy]

The VRAT article is long gone.

Actually, it's not "long gone". It's here:

https://www.radios-tv.co.uk/community/in...ge-tester/

As Chris says, claiming it's "long gone" is fake news.

Can I take this opportunity to remind GVR folks that we don't permit criticism of how other forums are run - please see Rule 4:

https://golbornevintageradio.co.uk/forum...ction=help&hid=8

I wasn't banned, I didn't rejoin. In fact it's a completely new site made with content from the old one, which was gone for ages. The original link IS gone, or in some fashion doesn't work.  No particular criticism was made.  The"link rot" is totally common. Wikipedia is full of it.

Mike, I don't want to make a big deal about this, but just for the record:

1. You explicitly said "The VRAT article is long gone". The article, not the link.
2. I didn't say you had been banned from VRAT. I said "some members have had issues with (or have been banned from) other forums".

Your writing style is very easy to misinterpret - it is too direct, too blunt, for a text-only medium - you need to soften your tone. I've said this more than once before - and each time I do, it is in response to complaints.

By way of example, instead of saying "The VRAT article is long gone", you could have said something like "I can't find a link to it right now". There's a huge difference between those two.

As it stands, you have falsely accused Chris of removing your article. Please try to understand and accept that. Please also understand that while I have no axe to grind personally, your writing style is causing us an increasingly disproportionate amount of work. This is unsustainable.

Finally, regarding point 2, the way that comes across is simple: you didn't read what I wrote properly. That worries me.

I am trying to help, I promise.

Mark

[radioman]

Michael,
I appreciate the time you've taken to describe your Neon-based capacitor leakage tester.
However, I do sometimes find it a bit difficult to follow what you've written, due to your rather terse writing style !
They say that "a picture paints a thousand words" so can I make a plea for you (and some others on the forum) to use circuit diagrams when you're describing a circuit please - It makes things so much easier to follow : a hand-drawn pencil drawing that can be photographed is all that is needed.

Thanks,
Andy

[ppppenguin]

I think I've got this right. The 100n across the neon doesn't need to be 630V. The neon strikes at no more than 150V, probably under 90V, so a 250V capacitor will be fine. The neon and 100n could equally be in series with the pair of 1M resistors rather than the -ve of the HT.  If you are certain that the voltage rating of your resistors is greater than the applied HT then a single 2M2 resistor can replace the pair of 1M.