Does the CRT deflection coil hold enough charge to zap somebody?

Once, and I repeat ONCE, I pulled the connector for the deflection coils on an Electrohome G-07 RGB monitor THEN discharged the anode. That will wake you up when you grab the deflection coil connector. :) One of those DUH moments.

On Wed, 16 Jul 2008 08:48:29 -0700, "Nicole Bischoff" put finger to keyboard and composed:

A coil holds no charge. A capacitor does. However a coil's back emf may belt you if you interrupt its current flow.

- Franc Zabkar

If the set is on and you are playing near the CRT you will get zapped from the CRT and not the coil. If it is off you can get nailed by the 25 KV of the anode capacitance which can be there for days. I got knocked across the room once by a hand to foot discharge, some people get killed by it, and I now put my elbow on the chassis so only my arm gets hit, a big ouch but not dangerous except to your arm and finger nerves. Always discharge high voltage. I got nailed by a 2,000 volt capacitor on a microwave that had been off for 3 days, less voltage but a big uF cap. Bill Baka

Don't just discharge the anode one time, do it once, wait about 20 seconds and do a second discharge. There is a phenomenon that I can't recall where the charge is stored partially in the glass envelope and the voltage can rebuild up to a few kV after the initial discharge unless the initial short lasts for several seconds.

Bob Hofmann

Don't just discharge the anode one time, do it once, wait about 20 seconds and do a second discharge. There is a phenomenon that I can't recall where the charge is stored partially in the glass envelope and the voltage can rebuild up to a few kV after the initial discharge unless the initial short lasts for several seconds.

Bob Hofmann

I was taught that it is because the area of the effective capacitor formed by the internal anode coating, the glass, and the external coating, is so large compared to the single small discharge point, that much of the residual charge sort of 'rushes away' as far as it can to try to re-eqaulise itself into an evenly distributed high voltage. Then, over a couple of minutes, it spreads out again over the whole internal surface of the tube. If you discharge over a couple of minutes with a resistive probe, you don't get a problem.

Back in the days, I had an old anode lead cut from a scrap FBT, that fed into a small plastic box that had a number of 10k resistors in it, in series to up the overall voltage rating of them. Coming out of the other end, was a lead with a croc clip on it. You used to just hook this to the external coating grounding spring, and then plug the cavity connector into the tube. Then go for a cup of coffee. When you came back, the tube could then be dealt with in complete safety, including removing it for replacement.

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High voltage capacitors can even build up a charge just from handling. Thats why high quality high voltage capacitors are shipped with a shorting wire across the terminals. I've seen cases where stock room personnel got zapped by high voltage capacitors that did not have shorting wires. That's why I keep shorting wires on HV capacitors, and discharge any capacitors that do not have them.

There are a few interesting stories regarding shocks from TV's and other high voltage equipment at

Even with high quality instrumentation caps there is a memory effect with some of them. Read some of Bob Pease's stuff in Electronic Design and he has some stories about that. I'm an old analogue guy like him and just when I think I've seen it all something new comes along. Some Mylar caps are super low leakage but have a memory effect due to residual electrons finding their way, as do many other types. Ceramic are pretty good but not ideal, and since there are over 20-30 types, glass included, I can't begin to tell you how many circuits that looked good on the schematic didn't make it because of a cap problem. A glass CRT was never intended to hold much charge beyond that required not to fade at the end of a scan line before the next flyback pulse recharged it again. What Bob said above is still very true. Bill Baka

i still remember grabbing hold of the capacitor on my friend's science fair project tesla coil when it was off. yahoohooie!! i felt like a character in a warner brother's cartoon.

ed

____________________ Get a loada this. I was succesfully able to drill a pinhole into the picture end of a 20" cathode tube, thus eVACUating it. I then carefully broke off the neck, containing the electron guns. Now realize that this neck is still fully intact and connected to the motherboard of the TV.

So using a very long set of grilling tongs for gripping hotdogs, with rubber-gloved left hand, and with my right hand turned on the TV at the moment Brian Williams is "thanking us all for watching" NBC nightly news.......

After a brief shower of red, green, and blue sparks and a lot of loud crackling, Brian Williams' FACE is now permanently etched on my ceiling! A little trapezoidally stretched, but it is him - of that I'm certain.

-CC

rd the St00pid Bullis says so on 24hoursupport.helpdesk.

I still like the Wells Gardner 4600s better.....never been a big fan of the g07's.