Don Maslin wrote: I prefer to do it "hot" since I can see what I am doing. Regardless, I once discharged a CRT fully (at least as far as I could touch the high voltage connection and not get a shock.) I left it alone for a while and went back to pick it up making the mistake of getting my hand too near the high voltage connection. After making the proper explatives deleted, I now always discharge the tube just before I am going to do something with it.

A teacher/mentor of mine repairs arcade machines during the summer. A new kid was assisting him fixing a Space Invaders (or was it PacMan?) machine. The kid said he discharged the tube and my friend believed him. The kid proceeded to start working on the tube and my friend was touching the chassis ground... with his left hand. His right hand came into contact with the kid's left arm, which was touching the HV connections... it literally threw him across the pub and he blacked out. When he came to, it was all he could do to keep from smashing the kid's face in. Kevin

At 09:56 PM 8/31/99 -0700, Don wrote: That's the smart way to do it! That CRT high voltage sure hurts! But beware that the CRT can act like a capacitor and store charges for a LONG time. I used to take new CRTS out of the shipping boxs where they had been sitting for a year or more and they would still bite me! Also most monitors and TVs have a hot chassis and one side of the AC line is connected directly to the frame. So unplug them before touching it and then ground a screw driver with a jumper and use it to make sure there are no stored charges anywhere. Joe

Tony, At 07:08 PM 9/1/99 +0100, you wrote: It should be now. Let me know how many chars/line you're getting. But they both hurt! Color TVs use ~25kV and if I remember right most B/W sets use ~18 to 20 kV depending on the CRT size. Unless the HV arcs. I've seen it happen more than once. Even 1000 volts isn't pleasant! Yeap, unless they've changed in the last couple of years. I've only worked on a few monitors so I'm not an expert but why take a chance? The TRS model I monitor was a modified TV. It and others like it would almost certainly have a hot chassis. Then you're lucky! Joe

At 07:08 PM 9/1/99 +0100, Tony wrote: I quess "hot chassis" isn't as clear as it once was. TV's don't have mains 60Hz power transformers like they used to. Are they many with 50Hz ones there? What they have is a mains rectified DC supply, typically 170V for 120V AC that runs the horiz. output stage. Much of the rest of the TV runs off the flyback transformer windings, which can be considered isolated. This is like SMPSU's except in a TV, the filter cap, horiz. output transistor, etc. may be scattered around the TV, and are all "hot", unlike many computer SMPSU where the mains side circuits are obviously apart from the output side. Of course, the horiz. driver has to somehow be powered to start up the TV, so may be hot as well. As for a "chassis" it has about disappeared. There is only the PC board, the CRT, and a pod with the controls, all in a plastic cabinet. Maybe ground could be considered the return of any inputs, or the CRT outer coating (not always the same circuit point) -Dave