Re: Does the CRT deflection coil hold enough charge to zap somebody?
- From: Bill <bbaka@xxxxxxxxxxx>
- Date: Fri, 18 Jul 2008 18:06:38 -0700
hr(bob) hofmann@xxxxxxx wrote:
On Jul 16, 4:55 pm, Bill <bb...@xxxxxxxxxxx> wrote:Franc Zabkar wrote:On Wed, 16 Jul 2008 08:48:29 -0700, "Nicole Bischoff"If the set is on and you are playing near the CRT you will get zapped
<pa...@xxxxxxxxxxxxxxxx> put finger to keyboard and composed:
Richard the St00pid Bullis says so on 24hoursupport.helpdesk.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
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
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
.
- References:
- Does the CRT deflection coil hold enough charge to zap somebody?
- From: Nicole Bischoff
- Re: Does the CRT deflection coil hold enough charge to zap somebody?
- From: Franc Zabkar
- Re: Does the CRT deflection coil hold enough charge to zap somebody?
- From: Bill
- Re: Does the CRT deflection coil hold enough charge to zap somebody?
- From: hr(bob) hofmann@xxxxxxx
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