Intermittent fault in Eizo 19" T766 CRT

[James Sweet]

I tried the tapping a bit more, and now the red gun also has this
problem... I
didn't tap that hard I think (from the description "not enough to break
it,
but close" I would think I need to tap a lot harder).

Now my question is: are those cathodes/filaments so fragile that I could
have
damaged them, or is it possible I dislodged dirt which now also affects
the
red gun?

The filaments were cold BTW, when I tried this. I suppose warm filaments
are
more easily damaged.

They could be that fragile, it depends, obviously one of them was fragile
enough to short in the first place. Now that you have two guns with issues,
there's no sense trying to isolate the heater because the guns would just
short to each other.

 

[Wiebe Cazemier]

They could be that fragile, it depends, obviously one of them was fragile
enough to short in the first place. Now that you have two guns with issues,
there's no sense trying to isolate the heater because the guns would just
short to each other.

I can't be sure, but it seems the blue gun has become much less sensitive, and
that the problem now is mainly is the red gun. Maybe it's wishful thinking,
because that would mean that it was some dislodged particle, but I'd rather
not assume the worst yet, so...

Would anyone know if trinitron tubes have particularly fragile heater/cathode
constructions?

The repair FAQ has a comment about having to tap the neck quite hard: "not
enough to break it, but close". How fragile is the neck? It would be difficult
to describe how hard I could hit it without breaking it, but any advice is
welcome.

 

[Wiebe Cazemier]

I can't be sure, but it seems the blue gun has become much less sensitive,
and that the problem now is mainly is the red gun. Maybe it's wishful
thinking, because that would mean that it was some dislodged particle, but
I'd rather not assume the worst yet, so...

Would anyone know if trinitron tubes have particularly fragile heater/cathode
constructions?

The repair FAQ has a comment about having to tap the neck quite hard: "not
enough to break it, but close". How fragile is the neck? It would be
difficult to describe how hard I could hit it without breaking it, but any
advice is welcome.

I've got an additional question. When I put my continuity meter on the GND and
R or B pin, I can't produce a short by any amount of tapping. A very brief
intermittant short should be very clear, because it has an audible beep.
Because I can only reproduce the fault when it's cold, having the heater
turned off would seem ideal.

What I want to do, is remove the neck board and do some more testing. Do I need
to discharge the tube for this? I would guess not, but I thought I'd ask.

 

[James Sweet]

I've got an additional question. When I put my continuity meter on the GND
and
R or B pin, I can't produce a short by any amount of tapping. A very brief
intermittant short should be very clear, because it has an audible beep.
Because I can only reproduce the fault when it's cold, having the heater
turned off would seem ideal.

What I want to do, is remove the neck board and do some more testing. Do I
need
to discharge the tube for this? I would guess not, but I thought I'd ask.

On Ground, or on one of the heater pins?

You might wanna just leave well enough alone and use the monitor the best
you can as it is.

 

[Wiebe Cazemier]

On Ground, or on one of the heater pins?

Neither produces a short. But the heater and GND give me 1 ohm resistance,
which I guess rises when it heates up. So in cold state, measuring between
heater and a gun and GND and a gun is about the same.

I can't think of another way for the gun to be fully turned on when it's not
connected to anything, but the multimeter hasn't shown a short, which is
strange. You wouldn't know of any other possible cause, would you?

You might wanna just leave well enough alone and use the monitor the best
you can as it is.

The red gun error is quite severe at the moment. It also keeps shutting down
when it occurs, so it's not very usable. I don't understand BTW why it does
shut down when red is shorted, and not when blue is shorted. It can't be
because the driver output is shorted, because I disconnected the plug for
it...

 

[Wiebe Cazemier]

On Ground, or on one of the heater pins?

You might wanna just leave well enough alone and use the monitor the best
you can as it is.

Another question: is it bad for the cathodes to run the tube with the heater
disconnected? I would like to do some measurements, but I'd rather not keep
the monitor on while the cathode(s) is/are being shorted to the heater.

If I keep G1, G2 and GND connected, is that enough to prevent damage to the
tube?