Re: Blurry Apple II GS RGB Monitor

[mjmahon@aol.com (Michael J. Mahon)]

Matthew Russotto wrote:

>In article <20020107140602.15037.00000271@mb-ba.aol.com>,
>Michael J. Mahon <mjmahon@aol.com> wrote:
>>
>>As long as one end of the wire is securely connected to chassis
>>ground, you can hold it just about any way you want.  You only
>>need it to be the first thing that comes into contact with the CRT
>>anode.  No insulation is necessary, since the wire is guaranteed
>>to be at ground potential by its _good_ connection on the other
>>end.
>
>Don't count on it.  AC (and impulses count as AC) sometimes doesn't
>follow the obvious path to ground.  Sure, theoretically you can stick a
>well-grounded bare wire under the suction cup while holding it with a
>sweaty hand and not get any sigificant current through you.  But I
>wouldn't bet on it myself.

First, note that in another thread I recommended that one not learn
to work on electronics with monitors (nor with power supplies).

Having said that, I assume that the reader knows what a good
connection is, and that the anode potential of a CRT is _not_
AC, but DC.  When the monitor is _off_--the only time to be
discharging the anode--it is _guaranteed_ to be DC, since it's
a charge stored on a capacitor (formed by the inner anode
electrode of the CRT and the exterior conductive coating).

TV techs have been using grounded screwdrivers and probes
for decades to discharge CRTs, and it is perfectly safe when
done properly.  "Properly" includes discharging it more than
once, with a second or two in between, so that the CRT is
surely discharged (there is often some remanent polarization
of the glass which induces a much smaller, but potentially
shocking, voltage on the presumably discharged anode).

Many inexperienced folk (and we all start that way) have
received substantial shocks from undischarged CRT anodes,
and one of the popular responses to bad experience is the
creation of superstition about it.  The greatest danger from
a charged CRT is not shock--which is "shocking" but unlikely
to cause harm in itself--but implosion of the CRT envelope.
A rapidly jerking shocked arm holding a tool in the vicinity
of the CRT--particularly in the vicinity of its neck--is a very
dangerous thing.  Flying glass from a CRT implosion can
do considerable harm to eye and body.

Be careful, but don't be superstitious.

-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/