Wiebe Cazemier wrote in
b.home.nl:
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?
If I remember correctly, the short was located via the earlier testing,
rotating a switch to localize the short.
You would then charge up a capacitor that was built into the tester and
then discharge the capacitor through the short via a pushbutton switch.
As I
mentioned in my other post, I thought there were three line wires, but I
can only discern one; is that the one?
[
http://en.wikipedia.org/wiki/Trinitron]
Another feature was a three cathode single electron gun arrangement, in
contrast to the then-dominant (and still common) three gun arrangement.
Single gun systems tend to be easier to manufacture reliably, simplify beam
focus and control, and are less prone to inter-electrode short circuits.
[unquote]
And the cathode line capacitor BTW, where is that likely to be located?
Near the flyback on the mainboard?
Sorry, no idea. But I think you are mistaking which capacitor is going to
be used to clear the short.
Good luck with your experiment. Hopefully, it won't drop something into
the center of the shadow mask.
Aperture grill mask, actually 
Correct.
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...
Intermittents are very problematic.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
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