Hi,

My 4 or 5 year old Eizo T766 19" CRT began showing an intermittant fault
yesterday. Sometimes the screen contracts a bit and comes back with wrong
colors. An example is that the screen turns very blue, and you can see the
diagonal vertical retrace lines in blue running over the screen (at least, I
assume they are the retrace lines). When the screen snaps back, it's often too
greenish, but turns normal over the course of a few minutes.

I had it open yesterday, and a couple of times, I could reproduce the fault by
touching the cathode assembly, so I thought it was a physical error, like a
loose contact. And just now, when it did it again, the monitor responded to me
hitting it (gently...). But, I couldn't reproduce it consistently, yesterday
or now.

I have a couple of questions.

1) A couple of times, the fault caused the monitor to go into off mode. At
least, the power led turned yellow, which it normally does in offmode. Is it
likely that when the fault is somewhere in a late stage as the cathode
assembly, that the control electronics is aware of it?

2) Should I want to refit the plugs connected to the cathode assembly (three
big wires; are those the RGB line voltage wires?), I would need to discharge
the CRT. I've seen a lot of videos of people just sticking a screwdriver
connected to the metal chassis under the anode plug, but is that safe? I've
never discharged a CRT before, so I'm kind of apprehensive.

3) How vital is it to discharge the power supply caps? If so, how does one do
that?

Any other insight is welcome, of course.

Thanks in advance,

Wiebe Cazemier

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

My 4 or 5 year old Eizo T766 19" CRT began showing an intermittant fault
yesterday. Sometimes the screen contracts a bit and comes back with wrong
colors. An example is that the screen turns very blue, and you can see the
diagonal vertical retrace lines in blue running over the screen (at least,
I
assume they are the retrace lines). When the screen snaps back, it's often
too
greenish, but turns normal over the course of a few minutes.

I had it open yesterday, and a couple of times, I could reproduce the
fault by
touching the cathode assembly, so I thought it was a physical error, like
a
loose contact. And just now, when it did it again, the monitor responded
to me
hitting it (gently...). But, I couldn't reproduce it consistently,
yesterday
or now.

I have a couple of questions.

1) A couple of times, the fault caused the monitor to go into off mode. At
least, the power led turned yellow, which it normally does in offmode. Is
it
likely that when the fault is somewhere in a late stage as the cathode
assembly, that the control electronics is aware of it?

2) Should I want to refit the plugs connected to the cathode assembly
(three
big wires; are those the RGB line voltage wires?), I would need to
discharge
the CRT. I've seen a lot of videos of people just sticking a screwdriver
connected to the metal chassis under the anode plug, but is that safe?
I've
never discharged a CRT before, so I'm kind of apprehensive.

3) How vital is it to discharge the power supply caps? If so, how does one
do
that?

Any other insight is welcome, of course.

Thanks in advance,

Wiebe Cazemier

I would suspect bad solder joints in the area where you can induce the fault
by tapping. It *may* be a short inside the CRT, but don't condemn that yet.
Don't worry about discharging the capacitors, just unplug it for 10 minutes
or so and it should be safe. Even when you're sure everything is dead, treat
it as live just in case.

On Friday 25 April 2008 18:38, James Sweet wrote:

I would suspect bad solder joints in the area where you can induce the fault
by tapping. It *may* be a short inside the CRT, but don't condemn that yet.
Don't worry about discharging the capacitors, just unplug it for 10 minutes
or so and it should be safe. Even when you're sure everything is dead, treat
it as live just in case.

And what about the CRT? Is discharging as I described safe?

When the fault is in the CRT, I assume nothing can be done? Well, let's just
hope it's not that; those Sony Trinitron tubes are pretty good, so I guess the
chance is small. But on the other hand, because after a fault, the screen is
greenish, which turns OK over the course of about 30-60 minutes, heating
cathodes may very well be it. The cathode assembly itself doesn't heat up that
fast.

"Wiebe Cazemier" wrote in message
.home.nl...
On Friday 25 April 2008 18:38, James Sweet wrote:

I would suspect bad solder joints in the area where you can induce the
fault
by tapping. It *may* be a short inside the CRT, but don't condemn that
yet.
Don't worry about discharging the capacitors, just unplug it for 10
minutes
or so and it should be safe. Even when you're sure everything is dead,
treat
it as live just in case.

And what about the CRT? Is discharging as I described safe?

When the fault is in the CRT, I assume nothing can be done? Well, let's
just
hope it's not that; those Sony Trinitron tubes are pretty good, so I guess
the
chance is small. But on the other hand, because after a fault, the screen
is
greenish, which turns OK over the course of about 30-60 minutes, heating
cathodes may very well be it. The cathode assembly itself doesn't heat up
that
fast.



You shouldn't have to discharge the CRT, that's only necessary if you have
to remove the anode lead, even then it usually discharges itself through the
focus divider on color monitors.

The 22" flat trinitron tubes commonly have intermittant focus issues, mine
acts up occasionally but has behaved pretty well lately. Haven't run into
that with the 19" tubes.

E"James Sweet" wrote in
news:90vQj.50$5X.10@trndny08:

You shouldn't have to discharge the CRT, that's only necessary if you
have to remove the anode lead, even then it usually discharges itself
through the focus divider on color monitors.

Caution: even if you discharge the CRT, if the anode lead is disconnected,
as the dielectric (glass in this case) 'relaxes from the stresses of being
charged', a charge can build back up.

I can remember drawing a nice arc many minutes after discharging the tube
the first time.

This can be a bit of a surprise, especially if you are removing the CRT to
replace it. Shocking, one might say.

Also, the comment about letting it sit for 10 minutes so all the capacitors
will be discharged is good, assuming that there are no open bleeder
resistors, etc. But, it might NOT be good to 'bet your life' on the
bleeders doing their job. Occasionally, they do open, so your caution to
treat them as if they might be 'live' is a good one for those that want a
long life.

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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"bz" wrote in message
98.139...
E"James Sweet" wrote in
news:90vQj.50$5X.10@trndny08:

You shouldn't have to discharge the CRT, that's only necessary if you
have to remove the anode lead, even then it usually discharges itself
through the focus divider on color monitors.

Caution: even if you discharge the CRT, if the anode lead is disconnected,
as the dielectric (glass in this case) 'relaxes from the stresses of being
charged', a charge can build back up.

I can remember drawing a nice arc many minutes after discharging the tube
the first time.

This can be a bit of a surprise, especially if you are removing the CRT to
replace it. Shocking, one might say.

Also, the comment about letting it sit for 10 minutes so all the
capacitors
will be discharged is good, assuming that there are no open bleeder
resistors, etc. But, it might NOT be good to 'bet your life' on the
bleeders doing their job. Occasionally, they do open, so your caution to
treat them as if they might be 'live' is a good one for those that want a
long life.



Yes if you disconnect the anode, you should definitely discharge it again
before you touch it, I usually leave a clip lead connecting it to the ground
strap so that doesn't happen. The zap won't hurt you, but it's enough of a
surprise to drop the thing or cut your hand open. In this case he shouldn't
have to disconnect the anode though.

On Saturday 26 April 2008 04:25, bz wrote:

Also, the comment about letting it sit for 10 minutes so all the capacitors
will be discharged is good, assuming that there are no open bleeder
resistors, etc. But, it might NOT be good to 'bet your life' on the
bleeders doing their job. Occasionally, they do open, so your caution to
treat them as if they might be 'live' is a good one for those that want a
long life.


OK, but since I will need to solder and/or refit plugs, I can't consider it to
be 'live' at all time. Will it be sufficient to measure the voltage between
the RGB line wires, for example, and ground, to give me an idea of whether
it's safe?

On Saturday 26 April 2008 02:51, James Sweet wrote:

You shouldn't have to discharge the CRT, that's only necessary if you have
to remove the anode lead, even then it usually discharges itself through the
focus divider on color monitors.

So discharge through the cathode assembly won't happen?


The 22" flat trinitron tubes commonly have intermittant focus issues, mine
acts up occasionally but has behaved pretty well lately. Haven't run into
that with the 19" tubes.

Focus issues are not my problem. When there is a fault, the screen flashes a
couple of times, contracts, expands (like an old TV) and sometimes it shuts
itself off.

Wiebe Cazemier wrote in
b.home.nl:

On Saturday 26 April 2008 02:51, James Sweet wrote:

You shouldn't have to discharge the CRT, that's only necessary if you
have to remove the anode lead, even then it usually discharges itself
through the focus divider on color monitors.

So discharge through the cathode assembly won't happen?


The 22" flat trinitron tubes commonly have intermittant focus issues,
mine acts up occasionally but has behaved pretty well lately. Haven't
run into that with the 19" tubes.

Focus issues are not my problem. When there is a fault, the screen
flashes a couple of times, contracts, expands (like an old TV) and
sometimes it shuts itself off.

Sounds like you might have an intermittent short to ground on a power
supply line, perhaps inside a bad capacitor.
Or an intermittent connection in the voltage sensing circuits, or the AC
line into the power supply.

Intermittents are difficult to localize and fix.

Perhaps you can narrow down the problem by monitoring voltages at various
points while it is acting up.



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap