On Sunday 27 April 2008 15:14, bz wrote:

If you are SURE that no vibrations from your tapping traveled elsewhere,
that is a strong clue.
Otherwise it can be a misleading clue.

I have played the 'taps' game and won. I have played it and lost.
It is best when you can make smaller and smaller taps while getting closer
and closer to the problem.

If the tap will only occasionally trigger/fix the problem, then it is easy
to be misled.

I know what you mean. Just yesterday, I had another CRT open, which often has
one or more of it's colors failing. You can fix it by smashing it, but when I
had it open, I could fix it by very gently touching the neck board. In that
case, it was clear where the fault was. In the case with this Eizo, I can tap
the neck board a lot harder without it doing anything, so you're right in that
it could very well be something else.

When I had a TV repair shop, in the early 70's, we had a tester for picture
tubes.
It had a short indicator and a 'remove short' button that discharged a
capacitor through the short.
Sometimes it would fix things. Sometimes it would make things worse.

I assume that would connect between chassis ground and cathode? As I mentioned
in my other post, I thought there were three line wires, but I can only
discern one; is that the one?

And the cathode line capacitor BTW, where is that likely to be located? Near
the flyback on the mainboard?


Good luck with your experiment. Hopefully, it won't drop something into the
center of the shadow mask.

Aperture grill mask, actually


Be aware that with 15 lb of air pressing on each square inch of the CRT,
you are playing with a live bomb.

I once took a picture tube out, laid it on its faceplate, got about 50 feet
away and tossed rocks at it.

Woomp. Dust and dirt and glass flew everywhere.

Chunks of the face plate (glass about 1 1/2 inches thick) landed about 50
feet BEHIND me.

Now, I would want a thick sheet of lexan between me and any CRT that I was
tapping upon, and safety goggles, gloves.

I was very careful, because I really didn't want to break anything. But anyway,
I wasn't able to fix the problem. I'm looking at the screen right now, and as
I'm typing this, it just flashed again. I don't know if I can or should tap
harder, but I wouldn't feel too comfortable trying it.

It's really annoying that I can't reproduce the fault reliably... Even if it is
a short between the blue gun and ground, I couldn't even short it out with a
cap, because the problem only every occurs for a fraction of second, very
sporadically...