Hi all,

In my years of swapping CRTs of any types I NEVER had this happen like
that, cracked projector CRTs face YES, have seen few caused by letting
coolant run out too low, CRACK! But this one is FULL of coolant and
tube self-destructed rather unique way.

The Blue CRT was initial tube we changed for discolored spot
complaint, prior to this swap TV was operating normally. After this,
couldn't do grey scale without poor picture and shutting down and unit
kept shutting down on brights. Helped if I turn down one of the
permeters in service mode, still shutting intermittently.

Changed other green and red CRTs got grey scale working but shutting
down persists. The TV simply cuts out and power blinks out and back
on trying come back then stayed on. Sometimes stays off. Can turn it
back on.

Our field manager we talked to for thomson says vertical problems and
I have not seen vertical collapse that could had broke this blue CRT.
I still don't buy that yet. Error codes were checked and it didn't
point to this area.

Drag that POS back and set it up to troubleshoot intermittent shut
downs displaying underscan pic of windows desktop via video input.
Turn around and getting stuff ready, turn around toward and see TV
dead. Found this broken CRT. GULP! Second blue CRT ordered and this
took record longest for order to come in. Was told that thomson had
to collect number of CRT and rebuild them because they were not making
new projector CRTs for these models.

Oh, I have to order string of yokes. Oh JOY Oh JOY! Edsel TV
strikes again; RCA in their infinite wisdom created 2 plug yokes
assembly all strung up in a row so you can't replace just one yoke out
of three. Oh joy!

Here's pics of this broken blue CRT. All pics are under 30K except
"two_piecesFLASH.JPG" is 45K

http://www3.sympatico.ca/jpero/final...nneck_yoke.JPG

http://www3.sympatico.ca/jpero/final...ackedFLASH.JPG


UP is front. Note spider cracks, one long across, and two small
diagontal cracks, on the side of CRT is a crack running towards neck.

http://www3.sympatico.ca/jpero/final..._facecrack.JPG


UP is front.

http://www3.sympatico.ca/jpero/final..._facecrack.JPG


View of a snapped off CRT & CRT neck.

http://www3.sympatico.ca/jpero/final...iecesFLASH.JPG


Cheers, Wizard

Dude !!!

I have looked at your pictures and I agree that in facecrack.jpg (i
think) the fluid level is low enough to not cover the entire face of
the CRT. Therefore a temperature gradient could indeed cause envelope
failure (a crack).

However when I got to the picture that depicts the neck of the tube
broken, I get red flags. I have seen it before, different brand etc,
but it doesn't matter.

You are getting a high voltage spike. The opening of a timing cap will
cause ONE pulse to be too big, and destroy the HOT or HVOT. When the
feedback loop for the main B+ is out, and softstart is out, what do you
think happens ?. Shutdown is working as designed, but it cannot react
fast enough. It cannot be made to react fast enough because of circuit
variables and many other factors.

Now you are here, and the set on which you are working has a nominal B+
of 76 volts, and has diffferent modes which DO kick up the 76. When it
goes into different scan modes, nominal might not be nominal.

I suspect that either due to a fault in the power supply or the basic
design, this set is getting boosted B+ when it is not in the proper
scan mode, or perhaps too soon if it is climbing scan modes.

Incidentally, when you get the high brightness shutdown, does it lose
the time and date ? My last one reverted to 1970 !

That PARTICULAR mode of shutdown did that, anything else did not. It
also defaulted to sattelite mode and just to get a picture you have to
go through a bunch of crapola.

When one of these comes in the shop (DTV30X) just double the normal
estimate and tell then to call you in eight months. You may think I am
kidding, but I am not.

Rather than talk to them about their pipe ****in dream, I would rather
make a sftstart/soft change tertiary addon for the power supply.

See RCA had finally discarded each and every one of the good ideas in
the world, then the execs ran out to the dumpster and got them back.As
near as I can figure, a rogue element inside the orginization
spearheaded the drive to develop this no-headed technology.

I must admit it was cool to watch the ATSC tuner find all them
channels, and I did watch it just a bit with the contrast down to about
a third.

MANUFACTURERS : Changing main B+ for scan mode changes is bad business,
even for you. Dont you remember how reactive scanning works ? What did
you think was going to happen when the set started back down in scan
rates ?

Yes, I am starting to really understand the DTV30X, but that makes me
like it all the less. If this isn't the folly of the century as far as
television goes, whoever tops it is likely to make the Darwin awards.

JD Wizard over here, I have been in this business a very long time and
am exceedingly successful, you have a HV spike.

In the ONE unit we got out the door, I limited it's scan settings, it
was no longer capable of certain modes. That is what it took.There was
also something else, some kind of retrieve info (I fergit) you need to
disable, because when it goes into that screen it lowers the scan mode.


If you get what I'm saying they were bad from the git. I however have
an idea. I can solve this, but do I want to ? This would involve
something to trigger into the main feedback opto that controls the SMPS
feeding the flyback. This may cause some abberations, but the set would
work, and continue to work. Either that, or I could do without all
their info, just put my own winding around the fly and use that,
exceed, even by a little bit, you powersupply drops out, and fast. We
would be removing filtering from the 76V line wherever possible. They
would be replaced with lower capacity, higher quality filters. This is
only on the line that feeds the flyback.

This is the only wrong way I can see to do the job right, and there is
no right way to do the job right, so figure the options.

JURB