Bump an earlier posting

  billyliv 08:26 06 Apr 2004
Locked

Hi, Would someone be kind enough to bump an earlier post Re- Electricity holding charge in CRT monitors?. I have to replace a 15 pin monitor cable, and it would be interesting to read through the comments before I start. Thanks, Bill.

  User-312386 08:29 06 Apr 2004

cant find it

did you post it?

  billyliv 08:33 06 Apr 2004

Hi, Unfortunately I didn't post it, but someone will have it in their postings. cheers, Bill

  billyliv 09:43 06 Apr 2004

Hi, Job done, Didn't get a shock. Cheers, Bill

  Gongoozler 10:02 06 Apr 2004

To clarify the situation regarding the high voltage in CRT monitors. The final anode voltage in a CRT is of the order of 35,000 volts. This charge is held on a capacitor which is formed by the metallised coating inside the tube, and the graphite based coating on the outside. The metallised internal anode is connected to via a stud in the wall of the tube. The external coating is usually connected to earth via a spring stretched accross the tube. The anode stud connects to a cable from the EHT (Extra High Tension) rectifier. This cable ends in a plastic shield to help prevent the connector from arcing to earth.

The capacitor formed by the metallised anode, the graphite earth coating and the glass wall as dielectric is very efficient at holding the electrical charge, and so may still have a significantly high voltage many hours, or even days, after switching off the power. The only real leakage path to discharge the capacitor is backwards through the rectifier. Disconnecting the EHT cable from the CRT removes even this leakage path.

For those familiar with working on CRT equipment, avoiding the areas where there is a risk of EHT discharge reduces the danger to acceptable levels, however to anyone else, the risk of a 35,000 volt electric shock is too high. This voltage can jump a remarkably long distance! I can say from personal experience that once having been on the end of a crt anode shock is enough to make a person very careful not to repeat the experience :-(.

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