2 Nov
2005
2 Nov
'05
8:13 p.m.
Wolfe, Julian declared on Wednesday 02 November 2005 22:52:
Okay, I'm going to try and take another crack at
replacing the flyback
on my VT100. A few months ago I almost did, and chickened out. I'm
very very afraid to do so, as the idea of trying to discharge the CRT
scares me very much. The terminal has been off and disconnected from
power for at least 2-3 months now.
This is what I've learned so far from reading:
Put one hand in your back pocket. Use an insulated screwdriver with
alligator clips on either end, one to the screwdriver blade, one to
the frame (VT100 service manual says the frame right above the CRT is
where you should ground to). Place the screwdriver under the anode
cap and touch the metal connection underneath. Wait till the
crackling stops. Remove the anode cap.
Can anyone reassure me that this is a semi-safe procedure? Has anyone
done this sort of thing before?
Yeah, I've replaced CRTs and flybacks before.
A better idea is to place a current-limiting resistor in series with the
alligator clip to ground (twist one lead around the screw driver, and
tape it on, attach the allegator clip to the other lead). 100k to 1M
ohm should do the trick, and hold it on the metal part of the anode cap
for 5 seconds or so. Not using the resistor will still discharge the
tube, but it runs the risk of damaging it.
If you have the tube powered off for a couple days, the charge will most
likely be quite dissipated. In fact, having it off that long means it's
unlikely to have any charge on the tube at all, but it's still best to
still discharge it, just in case.
Of course, I've worked on monitors live before. Trick there is to stay
clear of the PSU and HV parts alltogether, and use insulated tools.
Once you do it once or twice, you'll start feeling a bit more
comfortable doing it. It isn't a good idea to *replace* the flyback
with the terminal live, but you'll probably need to have the power on
when you adjust the screen/focus controls on the new flyback you
install.
Pat
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