Dead pixels on CRT

Faulty digital frame buffer.

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Adrian C

Sylvia Else Inscribed thus:

I've never seen a crt with a line of dead anything ! If its a dead straight vertical line then its unlikely to be the crt. Possibly some artifact of the video feed... maybe ?

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Best Regards:
                Baron.

It processes the signal as digital then converts to analog for the CRT driver. I'd guess it is not going to be worth trying to fix, something is gone in the digital section(s).

PeterD wrote in news: snipped-for-privacy@4ax.com:

some chip in the frame memory?

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Jim Yanik
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Could it possibly be a stabilising wire as in the Trinitrons(I know they are usually horizontal)

Ron

It doesn't. :> I suspect there are *two* "lines of dead pixels" in this CRT -- though only one is probably visible (luck?).

There are two (3?) wires that cross the screen (usually horizontally but since this is a wider aspect ratio screen, they might be oriented vertically) used to stabilize the aperture grill.

It's a Trinitron tube. This type of CRT doesn't use a shadow mask. Instead, it uses a shadow grid - a bunch of very fine parallel vertical wires, stretched from top to bottom.

An occasional fault in a Trinotron is for one of the shadow wires to end up out of position. If I recall properly, this can happen if somebody uses an external degausser - the magnetic field can shove one wire across the one next to it. This will cause a subtle vertical stripe to appear on the screen.,. looks rather like a row of dead pixels.

I think there's a Field Engineering Repair procedure for this... rapping sideways on the case, with just the right amount of force, to jar the stuck wires apart and allow the displaced one to snap back to its correct position. I don't know how much force is required.

One can sometimes see this effect even on a perfectly good Trinotron tube... I think that in some models there are vertical reinforcing rods in the grid assembly which can produce a shadow on the tube.

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Dave: Thanks for those notes. I wasn't aware of the vertical wire grid in a Trinitron tube. I knew about the two horizontal ones. I can actually see those in my screen.

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Best Regards:
                     Baron.

I'd be surprised if a television like that had a frame buffer. What would it be for?

Sylvia.

The set features a digital tuner.

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Adrian C

Fair point. Still, if the pixels were dead only in digital reception mode, I think the seller would have said so.

Sylvia.

Good question. I've only ever seen a fault like that on an LCD panel.

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It has a DTV tuner, thus it has digital storage and one or more frame buffers.

However, I would be skeptical that a digital failure would result in a vertical line fault in a non-flat panel TV, though might be possible.

Has anyone contacted the seller to get a more detailed description of the appearance of the "dead pixels" or a photo? Also, a CRT fault will stay fixed on the screen regardlerss of the mode or any adjustments while soemthing in the digital processing would almost cerrtainly not.

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The stuck shadow wire concept seems reasonably plausible, though I'd expect it to produce a line of bright pixels next to the dark ones - electrons from more than one cathode reaching the phosphor.

Sylvia.

I'm not even sure what "dead pixels on a CRT" actually means.

I've seen one or two CRTs with missing phosphor spots, but they're extremely rare, as they wouldn't normally get through QC.

A vertical line of them is hard to believe. And as for tangled aperture-grille wires... I've seen this on a 36" Sony (in fact, we discussed it several months ago), but all it did was badly screw up the purity.

It goes without saying that if the "defect" comes and goes, or moves with the program material, it can't be in the tube.

A photograph would be really useful.

Read the specifications, the video is digital to the CRT. Basically a 'cross-over' model on the way to full (LCD etc.) digital. Frame buffers are not unusual in these types of sets (the wide-screen variety)

Freeze pic/digital zoom in/out.

How about pic in pic?

End users aren't usually very good at describing symptoms accurately. It's entirely possible that the fault is actually as you've suggested. I'd try degaussing the middle of the line, in the hopes of shaking the wire loose.

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    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
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