20-07-2020, 02:07 PM
(This post was last modified: 20-07-2020, 02:09 PM by 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!
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!
