Re: Apple 2gs monitor

[rubywand@aol.com (RUBYWAND)]

In article <4ljv9g$ao@newsbf02.news.aol.com>, rubywand@aol.com (RUBYWAND)
writes:

>....
>    First, be safe. (See safety stuff at end.)  Mainly, unplug the
monitor
>and let sit for a day, wear goggles, work on non-conductive table
surface,
>do not stress CRT neck.
>....
>

     An email response from J.L.W. expressed concern that letting the
monitor sit unplugged for a day will not guarantee that the charge is
drained-off: 

>>
I assume this is to give the charge (20,000+ volts) time to leak. Just
might not happen if you are in a low humidity location and the tube,
etc., are all of good quality. .....
<<

     If, despite repeated warnings, there is any doubt: Anyone undertaking
CRT repairs should assume Dangerous Voltages _are_ present. Letting the
monitor sit unplugged for a day or a week does _Not_ guarantee the
voltages will be gone.

     After the monitor has been sitting unplugged for a day or so, J.L.W.
suggests discharging the anode lead using a well-insulated clip wire and
small screwdriver. This procedure, itself, is hazardous. It will reduce
the shock hazard while you work; but, it will _Not_ guarantee dangerous
voltages are absent.

     If you decide to do it: Wear Goggles. In fact, Goggles should be worn
for any work near a CRT  (i.e. "the picture tube").

     Some repair people like to wear rubber gloves. Well-fitted rubber
gloves can supply some protection; however, some are more pourous than
they appear and most are easily pricked by sharp circuit points. Thin
gloves are of dubious value around high voltages. Heavy gloves can lead to
fumbling a grip on a tool and, so, be an actual hazard. In general, if you
wear rubber gloves, it is a good idea to behave as though you were not.

     The monitor should be sitting, with the case back removed and out of
the way, on a non-conductive, uncluttered table.

     Often, the back of the CRT  is conductive and  may carry a dangerous
charge-- do not touch it.

     At all times be careful not to stress or bump the CRT's neck. The
main purpose of the Goggles is for protection should the CRT be broken. If
the CRT breaks, there may be a relatively peaceful THOOP; OR, there could
be a very nasty spray of glass!  

     The monitor should be oriented so that it is easy to get to the High
Voltage anode lead where it connects to the CRT. The anode lead is a fat
wire running from the top of the black H.V. module to a suction-cup
insulator on the CRT

     A "clip wire" is a length of insulated wire (about 2 feet long) with
insulated clips on each end. It has been checked visually and with an Ohm
meter to make sure there are no breaks and that it conducts from clip to
clip.

     The small screwdriver has a thin (about 1/16" to 1/8" diameter),
non-insulated shaft and a well-insulated handle.

     When discharging something, expect to hear a POP! It is a good idea
to 'expect to be surprised' and to be positioned so that, if you jump or
jerk back, you will not bump the monitor or break something.

     Use _No_ heavy pliers, screwdrivers, cutters, etc. anywhere near the
CRT. It is too easy to jump or slip and break the CRT neck.

     The HV anode lead connects to the CRT via a spead-out spring clip
inserted into a metal hole socket melded into the back of the CRT.

   ---     ---
==  \   /  ======= CRT back
       \ / <-- HV spring clip inside "suction cup" cover
        |
        | <- HV anode lead (goes to HV module)
 

     Clip one end of the clip wire to a metal sheet (ground) part of the
chassis. Clip the other end to the small screwdriver's shaft. Holding the
screwdriver's handle, touch the tip to the back of the CRT near the HV
anode connection. There may be a discharge POP. Touch the tip to the
surface several times.

     Carefully slip the screwdriver tip under the HV anode suction cup
cover. Probe to contact the metal clip. There may be a loud discharge POP.
As above touch the tip to the spring clip several times.

     You can use the same method for discharging other circuit points. An
example is the set of contacts on the underside of the motherboard where
the HV module is connected. There will not always be a noticable spark or
POP.

     Like other precautions, discharging reduces the risk of a shock; it
_Does Not_ eliminate it. It is difficult to discharge all dangerous points
or, even, to be sure any point is completely drained of charge. Also, even
a small shock can be dangerous if it causes you jump and bump into
something.

     Once finished with discharging, you can greatly reduce shock hazard
by following a simple rule: never touch two circuit points at once;
especially, never touch the metal chassis and any other circuit point.


Rubywand