Discharging a VT100 CRT

Well, glass [1] is an excellent insulator and could hold a charge for 3 months _but_ it is very likely the CRT has discharged either through leakage in the EHT rectifier diode (built into the flyback in this unit), or through the beam current when the thing was last used. The worst case for the CRT to hold a charge is if the EHT side (flyback, etc) keeps working and there is no beam current due to the grid being very -eve or the heater going out, or... There is then nothing to discharge the CRT. [1] The capacitor you are discharging consists of aquadag layers on the inside aod outside of the CRT flare. The CRT glass envelope is the dielectric. More particularly, work one haned, keep the other hand well away from the unit and anything that's earthed. The most dangerous current path is up one arm and own the other. It is normal to keep your left hand in your pocket. Some say it's because your heart is on the ledt side, I personally do it because I am right-handed. You should connect to the CRT earth. I seem to rmemeber on a VT100, that's a spring contact on the yoke with a white wire/faston clip. The idea is to ensure that the discharge current doesn't flow through anything it shouldn't It's safe for _you_, but I wouldn't do it that way. The high initial current could damage the CRT (burn the conenction between the anode conneector and the internal aquadag layer), and more particularly could damage IC's all over the terminal. The first thing I'd do is take out the logic board(s) and PSU. That gets all the delicate ICs out of the way. I would also use a discharge resistor. Take a 1M resistor (or if you prefer 10 100k resistors in series if you're worried about the voltage rating), connect one end to the CRT earth, the other to the screwdriver blade [2]. Carry on as above, but hold the screwdriver in contact with the anode conenctor for a minute or so. If you're worried, repeat the process with no resistor just to be sure. [2] Don't do what I did once when inebriated [3] and connect both the chassis and screwdriver to the same end of the resistor, thus not having it in-circuit [3] Why was I working on a monitor when drunk? Well, it was my 21st birthday, one of the presents was a non-working FTS-88 computer. Of course I started to repair it ASAP. The charge stored in a normal-size CRT -- particularly a monochrome one -- is not likely to be dangerous in itself to anyone without heart problems. But it will make you jump, you might then drop the CRT with very unpleasant results. -tony