Electronics Forum / Electronics / June 2003

I don't know about modern sets or monitors - but with many of the 80's
models I worked on some years back  - there was still quite a healthy
ZAP to be had from under that ultor cap for some time after turning
off power to the set/monitor.  Some sets did - some didn;t.  but
personally its not a chance I would take.

I even had several of these old computer monitors of the same model
that would run for about 30 seconds and then fail.   Fault turned out
to be high voltage capacitors that had failed in the horizontal output
stage and caused the EHT to go sky high before the x=ray protection
cut in and killed power.

The zaps that came from a couple of  these with  this fault conditon
were amazing.  in once case I saw a spark jump from under the sealed
ultor cap and across to the metalwork that supported the tube about
2-3 inch away from the cap edge.  

These certainly went off with a bang when ultor discharged even after
power was removed.  One even gave a nasty and painful shock (with the
mains removed) from putting my hand about an inch from the ultor cap

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Cleaning procedure I always followed was:

I would strongly advise earthing the ultor cap lead to the bare wire
that is spring loaded across the outside of the back of the tube.  I
used a multimeter lead typically for this - slide the long probe end
under the cap and discharge.  

Clean the hole, cap and surround thoroughly - immediately after
discharging and promptly replace the ultor lead in the hole.  

Pull it gently afterwards to make sure it has locked into the hole
properly and won't fall out.  

If it does fall - and lands on the PCB in the set - it might do a hell
of a lot of damage to components.