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longneck90 7th Dec 2017 5:57 pm

Work lamp
Hello to everyone, This query ? is not strictly anything to do with radio restoration, so, Moderators, please move it if it is in the wrong place. Yesterday, on switching on my worklight/magnifier light, it didn't come on. I wriggled things about, ie. lamp, plugs, connecting wire etc. Switching it on again, it was OK. I then probed the steel parts (springs etc) of the lamp with the electric neon tester, and the neon tester light came on. I closely examined all the wiring to the lamp, without dismantling it, but saw nothing suspicious. I then tried the neon tester on other devices, like signal generator, with no response from neon tester. I tested for voltage between the steel parts of the lamp and the chassis of a plugged in radio. Result, 1 or 2 volts. Nevertheless, I am worried about the neon tester lighting, when connected to the steel of the lamp. For instance, would there be an increased chance of something dramatic happening if I accidentally had one hand on lamp while the hand was touching radio chassis.
Any information would help to put my mind at ease. All the best. John.

G6Tanuki 7th Dec 2017 6:36 pm

Re: Work lamp
What kind of lamp is it? LED? Fluorescent? Incandescent-bulb? Does it have a separate transformer/controller/ballast-box or does the mains cable just run direct to the bulbholder??

It only takes a miniscule amount of leakage to light one of the usual neon-testers: the "creep resistance" of an old decaying bakelite bulbholder, or the mere capacitance of the live lead to the metal lamp as it runs through the metalwork, could be enough to cause such a tester to light.

longneck90 7th Dec 2017 7:45 pm

Re: Work lamp
Hello to all. To G6Tanuki, this light is about 2 years old. It is a 22W fluorescent magnifier light, fed directly from the mains. I just thought it strange, that the neon tester lights when contacted to the steel of the lamp, and doesn't do so when connected to other electrical devices. And!!! The neon tester lights, when connected to the steel structure of the lamp, whether the work light is switched on or not. Thanks for your advice. All the best. John.

OscarFoxtrot 7th Dec 2017 8:07 pm

Re: Work lamp
The only thing you can usefully do with a neon tester (screwdriver type) is put it in the bin. They're useless for testing and, if faulty, could kill you.

Use either a proper two-probe tester or a non-contact voltage detector (and the latter is not suitable for proving circuit isolation or safe-to-work condition)

vidjoman 7th Dec 2017 8:18 pm

Re: Work lamp
Check the mains lead - if it’s 3 core then it seems that the earth connection to the metalwork has come loose/broken. If only 2 core then it’s just stray from the cable and not dangerous, the neon tester will probably light if you hold it on the cable. They are NOT a good indicator.

ms660 7th Dec 2017 8:24 pm

Re: Work lamp
Well...If it indicated that a safety earth had come adrift then I would say in that instance it was a good indicator....


dseymo1 7th Dec 2017 8:30 pm

Re: Work lamp
Agreed re both neon testers and strays, although I often use a neon as a final reassurance check on things I already know are isolated.
It is a little worrying though that you're seeing volts on the metalwork *and* the lamp is intermittent, particularly if it's supposed to be earthed. It's possible that the cable is frayed somewhere, and warrants careful inspection IMHO.

longneck90 7th Dec 2017 9:56 pm

Re: Work lamp
Hello to all, Thanks for all the advice, which I am now digesting. I just want to say, from the point of view, of not knowing much about electronics, that the second thing I always do when approaching an unknown radio for the first time, is to check the chassis with my neon tester. If it lights, (the neon tester) I know that there is something not quite right, and so I then find out what it is. The first thing is to check that there is no short circuit or otherwise, by checking across mains leads. In this particular lamp, the neon will NOT light, when dragged along the mains lead. What I think is the best thing to do is get a new, similar lamp tomorrow. Maplin's is within walking distance. Meanwhile, thanks to everyone for the helpful and illuminating advice. All the best. John.

Refugee 7th Dec 2017 11:29 pm

Re: Work lamp
Those Maplin 22W lamps have a 2-core mains cable and mine produces a triangle wave of several volts peak to peak on a scope with the probe held an inch from the tube at something like 25Khz.

No wonder your neon tester produces a false signal. If you have got a Megger you can test between the plug pins and the metal work. It should be fine.

longneck90 8th Dec 2017 1:14 am

Re: Work lamp
Hello to all. To Refugee; Yes, that was one of the first things I done. (test between plug pins and metal structure) There was no continuity between probes, so I guess the lamp is OK. Thanks to everyone for helping to put my mind at rest. All the best. John.

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