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NotTaR of Television Sets : High voltage to focus short
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1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying.
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Symptoms would be (with the unit powered and high voltage present):
- With the CRT neck board plugged into the CRT, the focus spark gap is likely
arcing.
- With the socket unplugged, putting anything connected to ground (or any
other circuitry) near the focus pin would result in a juicy spark or arc.
WARNING: Removing the CRT socket and powering the set may destroy the CRT
on some models. See the section: Warning about
disconnecting CRT neck board.
If the CRT is gassy or up to air, forget it - it might make a decent fish
tank :-). In this case, there would be visible arcing INSIDE the CRT probably
not confined to a single location.
However, if there is just a metal whisker between the F and HV, that might
be able to be cleared by careful tapping or a charged capacitor. You may even
be able to see it if you were to remove the yoke - the gap is pretty large,
about 1-2 mm - the last gap between electrodes before the start of the
internal (Dag) coating.
See the section: Rescuing a shorted CRT.
Note that other damage may have been done as
Other components including the flyback, HOT, and parts on the CRT neck board
and beyond, may have been damaged as a result of the short. Zapping the CRT
may be just the beginning of what is required to repair it all.