Discharging a CRT
By Adam Whitlock
DISCHARGING
A CRT IS A DANGERIOUS PROCESS AND WILL VOID YOUR WARRANTY. THIS
IS A PROCESS FOR PROFESSIONALS ONLY. YOU HAVE BEEN WARNED!
Discharging a Cathode Ray Tube (CRT) can be a simple process, if
proper precautions are taken. Safety is very important to keep in
mind. A simple mistake could potentially cost a life, or at least
a bad headache and the shakes for a while. Discharging the CRT
itself is a simple process, and is the same on all CRT’s. Nothing
changes between displays and this guide can be used for an array of
displays. Same goes for televisions, though I would suggest taking those to a repair shop.
Safety
Your personal safety is top priority while discharging a CRT.
If tried and true methods are not followed, it could lead to some
potentially dangerous situations. Some people have had serious
damage caused due to the amperage going through their body and, as I
stress, deaths can occur. Using rubberized tools is
necessary. You can touch the CRT using any tool, but using a tool
with a rubberized handle keeps you from getting shocked by
accident. If you want to run the risk of using a plain plastic
handled tool, it’s your risk. It’s a stupid risk at
that. Other than using rubberized tools, having a clear work
environment is a must. If you are experienced at discharging, you
won’t need this guide, but for a beginner a flat surface will make
keeping the display steady since CRT’s are curved. On another
note, keeping your hands clean after touching the CRT and removing the
cap is a good idea. It’s pretty dirty in there, full of lead, and you
don’t want that stuff to end up on other parts of your body and/or food
you consume.
Discharging
Before attempting to discharge, I would highly suggest leaving your
display off for at least 10 minutes and unplugged from any
source. The first object you should look for is a
ground. It can be on a piece of metal attached to the chassis, or
the ground that is for the power cord. The analog (power) board
for the display has many ground points, so finding one should not be
difficult. After locating the ground, you will want to attach an
alligator clip from your discharge tool (see fig. 1) to the
ground. If the alligator clip slips find another ground point, or
reconsider getting a new tool.
Fig. 1 - Proper Discharge of a CRT using a rubberized tool and grounded to chassis
Fig. 2 - What it looks like under the cap. The arrow is pointing to what you touch with the probe.
Figure 3 - The cap and all of it's glory...
Figure 4 - Homemade Tool that, when attatched to a rubber handled
screwdriver can discharge the CRT as well as the real thing.
After grounding the tool, you will want
to place the probe under the CRT cap and make contact with the metal
clips that hold it into place (see fig. 2 and 3). This will discharge the CRT and
make the display ready to service. If you see sparks, then
you know the display has been discharge, but also you have not let
enough time for it to dischargen naturally. Next time you discharge this
particular display, double the amount of time you waited e.g. instead
of 10 minutes wait 20 minutes.
Pretty much, discharging a CRT is taking a probe from under the CRT cap to a ground on the chassis so you don't get shocked.
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