"Wiebe Cazemier" wrote in message
b.home.nl...
Hi,

Over the past few days I've been analysing a problem in my Eizo T766 19"
CRT
(Sony Trinitron tube), with this group's help. Unfortunately, I can
conclude
nothing else besides that the red and blue gun occasionally short to
something
at low potential, most likely the heater. I tried tapping it loose, but
with
no success. So, now I'd like to collect as much information as possible
about
zapping the short out.

I've seen suggested that you can use a neon transformer (or other kind of
tesla
coil) for this: connect both pins of the heater to eachother, and connect
the
transformer between it and the affected cathode (one at a time). This
seems
rather dangerous to me; such arcing usually leaves everything blackened.
If
this is a good approach, what voltage neon transformer should I look for?

Another method is a capacitor charged up to several hundred volts; start
with a
few uF, then increase as desired.

I would like to know, based on people's experience, how much chance I have
of
blowing out the cathode or filament. Bear in mind that it's an
intermittant
short, that does not show up on the DMM when the tube is unpowered (not
even
on the 200 MOhm range), so in the most positive situation, we're talking
about
loose debris which needs to get out of the way, and not a dead short.

One last question: is the heater filament an exposed (or covered?) fragile
filament like that in light bulb, or is more robust like heating wire of
an
electric stove?

Any help is appreciated, and thanks in advance.

Wiebe Cazemier

My B&K CRT analyser / restorer removed shorts by discharging a cap across
the affected electrodes. I seem to recall that g1-k shorts were actually
more common, due to 'burnt out' emissive material falling off the cathode
and lodging in the g1-k gap. The location of the short was indicated by neon
lamps, the intensity of the glow giving an indication of the resistance of
the path. When the zapping took place, I think that the CRT gun was being
run by the analyser as a basic triode. Some quite spectacular fireworks used
to occur in the neck, as the contaminating material was vapourised by the
discharge across it from the cap. It was very effective at removing
inter-electrode leakage paths. The B&K was a fine instrument in its day. I
lent mine to someone some years back, and it was never returned. I can't
even remember who it was to ...

CRT heaters are not particularly fragile, and are insulated from the cathode
cylinder, by a heat conducting coating. If you are discharging between h and
k, then the heater pins should be shorted together to avoid one of those
'unfortunate accidents' ... And of course, make sure that the base connector
is removed from the tube !!

Arfa