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teslacoolguy

Sat Feb 02 2008, 02:51AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
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Posts: 792

i was wondering if a crt can really kill you if you touched the anode because i have heard so many different theories about it ranging from people saying that they do not hold a capacitence at all after a couple of seconds of being off all the way to to holding a lethal charge even after months of being off and i want your opinion on what you think (not that im going to touch the anode of a crt anytime soon) but i wanted to get to the bottom of this.

Wirenut

Sat Feb 02 2008, 05:43AM

Registered Member #141 Joined: Sat Feb 11 2006, 01:14PM
Location: Southern California
Posts: 96

While I wouldn't claim that it's impossible for it to kill you, I will claim that it is unlikely. I can verify for sure that the crt can hold a charge for a long time (days or more) after being turned off, as I have been shocked by touching the anode wire in a monitor that had been unplugged for days if not weeks. It was not deadly, but it sure was painful. Definitely avoid this. On the other hand, I think the large electrolytic caps on the motherboard can hold a much more dangerous charge - I always discharge these first whenever working on a monitor or tv.

ShawnLG

Sat Feb 02 2008, 07:35AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
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Posts: 399

I don't know why you would want to touch the anode of the CRT but I always discharge it when taking apart a monitor or TV.

Dr. Dark Current

Sat Feb 02 2008, 08:43AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

There is often a "relatively" large (2-4nF) cap in the flyback which can deliver quite painful shock. I doubt that the CRT itself has nearly such high capacitance.

Bjørn

Sat Feb 02 2008, 09:42AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Often quoted numbers for the capacitance is 1 nF which would make it unpleasant but safe from the electrical standpoint. You will never be 100% safe since you may be seriously ill without knowing it or the schock may make you do something unsafe.

It is impossible to say how long the charge will be held, the only way to be sure is to discharge it.

Electrical Safety

Wolfram

Sat Feb 02 2008, 01:22PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

jmartis wrote ...

There is often a "relatively" large (2-4nF) cap in the flyback which can deliver quite painful shock. I doubt that the CRT itself has nearly such high capacitance.

Are you really sure about this? I've drawn arcs with many different flybacks, and if there were a cap in them, they would spark, not arc. 4nF at 30kV is just under 2J, and that would certainly be loud.

Although not likely lethal, a shock from a CRT would certainly be very painful. The capacitance depends on the size of the CRT, but I've also heard that around 1nF is the usual value for normal-sized TVs.

When left connected to the flyback, they can stay charged for weeks or months, maybe even longer. Discharge them if you're unsure.

teslacoolguy

Sat Feb 02 2008, 02:17PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Anders M. wrote ...

jmartis wrote ...

There is often a "relatively" large (2-4nF) cap in the flyback which can deliver quite painful shock. I doubt that the CRT itself has nearly such high capacitance.

correct about the flyback there is probably no capacitor but when i am drawing arcs or something when i turn it off there is a small charge stored inside the flyback for a couple of minutes but nothing major and also i have taken apart over 20 tv's over the past year and none of them had any sort of charge stored in the crt either they have been of for a REALLY long time or ive just been lucky

Dr. Dark Current

Sat Feb 02 2008, 02:22PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Anders M. wrote ...

jmartis wrote ...

There is often a "relatively" large (2-4nF) cap in the flyback which can deliver quite painful shock. I doubt that the CRT itself has nearly such high capacitance.

In most (if not all) monitor flyback there IS a cap (in TV ones just rarely, I don't know why). The cap often has a separate ground connection so you can still draw arcs if you don't ground the cap.

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