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From: stever@videovax.Tek.COM (Steven E. Rice, P.E.)
Newsgroups: comp.sys.amiga
Subject: Re: Monitor popping
Message-ID: <4674@videovax.Tek.COM>
Date: Mon, 9-Nov-87 15:37:18 EST
Article-I.D.: videovax.4674
Posted: Mon Nov  9 15:37:18 1987
Date-Received: Wed, 11-Nov-87 21:49:56 EST
References: <4754@burdvax.PRC.Unisys.COM> <1987Nov6.092619.136@mntgfx.mentor.com>
Reply-To: stever@videovax.Tek.COM (Steven E. Rice, P.E.)
Organization: Tektronix Television Systems, Beaverton, Oregon
Lines: 53
Keywords: My monitor goes POP and crashes my machine.
Summary: PLEASE be careful!!!

In article <1987Nov6.092619.136@mntgfx.mentor.com>, Rob Lucke
(rlucke@mntgfx.mentor.com) writes:

> [ comments about causes of monitor popping ]

>   Check for a properly connected ground on the monitor's CRT tube.  Do
> this VERY CAREFULLY since high voltage may be present inside the 
> monitor, even if it is unplugged (capacitors, static electricity, etc.).
> If you don't want to pay for a professional service person to do the 
> work, at least let the monitor sit unplugged for a while before you
> open it (this allows the charge to "leak" off).

PLEASE be careful if you follow this advice!!!  Leaving the monitor sitting
unplugged "for a while" can be deceiving.  The CRT can retain several
thousand volts for days or weeks!  Worse, if you ground the CRT anode (the
cap on the side of the tube) and then remove the ground, a phenomenon
known as "dielectric absorption" can cause several kilovolts (several
thousands of volts) to reappear within a few minutes of removing the 
ground.

If you feel the need to perform this operation, do these things:

  1. Have someone trained in CPR in the room with you.  Chances of fatal
     injury are small, but it is better to be safe than buried.

  2. Situate the monitor on a flat, insulating surface.  (Make sure it is
     stable -- you don't want to have it fall over on you or on the floor
     if a shock should cause you to move suddenly!)  Do not use a table
     with a metal edging or other exposed metal surfaces, so you do not
     become part of a path for current flow.

  3. CAREFULLY ground the CRT anode to the monitor chassis as soon as you
     have the case open sufficiently to do so.  Use reasonably heavy wire
     with a clip that attaches securely to the chassis and a flat, spring-
     loaded slide that can go under the rubber anode cap and maintain
     contact with the anode terminal for the duration of the procedure.
     (The flat slide must have an insulated handle so you don't have to
     hold it as it comes into contact with the high voltage.)

  4. Before touching the ground strap, ground it (and any other ungrounded
     metal) to the chassis using an insulated wire.

Leave the anode ground in place until the last possible moment.  Remove it
from the CRT first.  Then take the clip off the chassis.

These precautions are not guaranteed to prevent injury (nothing is fool
proof, since fools are so ingenious), but they do reduce the risks.

					Steve Rice

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