Film-Tech Forum ARCHIVE: Undead Pixel

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Posted by Lincoln Spector (Member # 6835) on 05-09-2014, 03:46 PM:

Hi, folks.

I attended two screenings at San Francisco's Castro Theatre over the past week, and noticed the same problem both times. There was a red dot in the lower-left corner of the screen. It was most noticeable in dark scenes, and disappeared entirely when that part of the screen was bright white.

I figure that it must be a red pixel stuck on, so that it is reflecting red light even when it's not supposed to do so. Hence the title (coined by a friend) "undead pixel."

I saw the same thing a couple of years ago on one of the screens at the Kabuki Theater (also in SF). That one was blue, but oddly, also in the lower-left corner. That one disappeared after awhile.

Can someone tell me more about these things, and how much it costs to fix them?

Thanks,

Posted by Carsten Kurz (Member # 5396) on 05-09-2014, 04:13 PM:

It costs 15.000-18.000 US% to fix it. If the machine is out of warranty. A lightengine swap.

There may be rare occasions where they disappear after a while, but most of the time, if they are there, they stay.

- Carsten

Posted by Paul Mayer (Member # 355) on 05-09-2014, 04:23 PM:

Oops, double posted with Carsten. In a TI-based machine each pixel is a tiny tiny micro mirror mounted on a piezoelectric crystal which moves the mirror to reflect light towards the prism or towards a light dump - usually when they get stuck in a given position, that's it, though they sometimes do free themselves up as you have noted. The only way I've heard of fixing them in the field is to replace the entire light engine. Definitely not cheap unless it's under warranty.

On at least the Christie machines there is a clean air source called a LAD (Laminar Air Device) which directs clean filtered air across the surface of each DMD imager both for cooling and to try to prevent dust particles from settling on each device. Also, sometimes the piezo mounts simply fail. When enough pixels get stuck, especially if those pixels are near the center of the image area, the entire light engine (all three imagers) will have to be replaced.

Posted by Sam D. Chavez (Member # 1841) on 05-09-2014, 05:51 PM:

Castro is aware of the stuck pixel and is pondering a repair vs. new 4K projector.

Posted by Randy Stankey (Member # 64) on 05-09-2014, 07:16 PM:

The digital equivalent of dust and scratches on film.

Maybe not as prevalent but WAY more expensive to remedy.

The inevitability of these types of problems in video versus film is debatable but a contentious film handler can minimize the problem below the threshold of perception with nothing more than common sense and attention to detail. With video, the solution is complicated, expensive and there is little that even a good operator can do to stop it.

This is not to say that film is better than video or vice versa. I am saying that the problems are roughly congruent and that this is prima facia evidence that the "dust and scratches" issue is little more than empty "digital evangelism."

If I am guilty of "film evangelism" it is only to say that digital ain't all that it is cracked up to be just because the digital evangelists say so.

Posted by Louis Bornwasser (Member # 3063) on 05-09-2014, 08:33 PM:

I agree. There are plusses and minusses to almost everything.

I was once asked when I was speaking to a large group of theatre owners: "What is the best projector?" My answer: "What problem are you most able to tolerate?"

Posted by Geoff Jones (Member # 3668) on 05-09-2014, 10:23 PM:

quote: Randy Stankey
The digital equivalent of dust and scratches on film.

I disagree completely. Dust and scratches on film disappear as soon as you get a new film (or a replacement print).

A stuck pixel is there for every single movie you show until the machine is repaired or it happens to go away.

Posted by Marcel Birgelen (Member # 6801) on 05-10-2014, 04:35 AM:

The fully-priced light-engine-swap thing really is a rip-off. The actual DMD costs a few hundred bucks at the most and sure, there is some labor involved in replacing it. It's probably not something you can do on location, but still, charging full price for a new light engine is still outrageous. I'm pretty sure those "defective" light engines get overhauled and serve as spares afterwards.

Posted by Steve Guttag (Member # 268) on 05-10-2014, 06:37 AM:

The DMDs for DCinema are more than a couple hundred bucks. Note, to the best of my knowledge, all of the DLP companies WILL repair a light engine. You have to allow for up to an 8-week turnaround though and it does save considerable $$$ since you are only paying for the freight, part and alignment time.

What this means though is that the FIRST failure you have of a particular light engine type (1.38 1.2, .98, .69) of any brand you have, you will have to buy a light engine (and they can be over $20K...with the 4K engines in the high $20Ks) so you can send the bad out out for repairs...when it comes back, put it on the shelf for the next one...so on the second failure, you are going to be below $10K and I hear closer to $5K for the repair.

I know one customer that is contemplating buying one of the small projectors like the NEC NC900C as a space saver spare tire so if his main projector ever fails, he can throw it in quick and dirty to keep going while the main projector gets repaired.

I think if you have a complex of any size (or a chain with several locations), it would be wise to have a spare projector on-site or in the region. It isn't a matter of "if" but "when" you will need a spare part NOW! I've had an ICP go down on a Friday night...try to get a part sent out on a Saturday! While Barco will ship 7-days and even same day...that will cost you body parts!

If you keep clones of your projectors, you should be able to get your spare projector up pretty fast...set up the lens files or just rob the part you need (whichever gets you up and going faster).

Posted by Frank Angel (Member # 248) on 05-10-2014, 08:40 PM:

Brad needs to invent the digital equivalent of FilmGuard that you can pour on the DMD and clean away stuck pixels. They are just mirrors after all. The DMDGuard would even lubricate the little micro hinges so lagtime will decrease; it might even make them less brittle...which can't be a bad thing!

They are lucky that stuck pixel was not somewhere in the center of the screen.

My fear is, that if history has shown us anything, it's that exhibitors are less that forthcoming when it comes to shelling out bucks to replace worn or defective parts. If you think a theatre owner who was reluctant to spend $800 to replace a xenon bulb that underlit his screen because it was way past its prime, imagine his reluctance in shelling out $20K just to shut off a single red dot somewhere on his screen.

And to follow Geoff's thought, dust and scratches go way with the next print, they are also very fluid and intermittent -- they are there one 1/24th of a second, gone the next. But my friends, that stuck red dot, no matter how minute, will stay in that picture throughout the ENTIRE film. Try as you might, you will NOT be able to ignore it and after awhile, it will start to look like a buring xenon headlight aimed right for your eyeballs. You think scratches are annoying? Just wait till this stuff ages and these things start popping up in theatres all over the place.

Luckily for patrons in ancient times (before digital), at least back then xenons past their lifespan eventually just wouldn't strike and they HAD to be replaced. But that chip is going to work on and on and on with its stuck pixel and it may never be replaced. [Eek!]

It's not a happy digital future I see.

Posted by Brad Miller (Member # 2) on 05-10-2014, 10:33 PM:

So if the red dot danced around all over the picture, sometimes dozens of red dots on EACH frame (but always in a different spot from frame to frame), then that would make it ok?

After all that's what people running film without FilmGuard had...constant little dots flashing to a minor or extreme amount (depending on the quality of the operator). Let's also not forget the CAP code too.

So just to make sure I'm understanding this, it's ok to have BLACK dots, but not a RED dot...or is it that IF the red dots danced around, then THAT would be acceptable?

[Razz]

One thing I will agree with, the "cheaper" theater owners out there are bound to just keep running with dead pixels, just like how they wouldn't shell out any money to change that bulb when it started to get dark, or for film cleaning supplies, or to pay for a competent projectionist, or for that matter...quality film equipment. It's all the same.

At least with digital when someone screws up the building of a playlist, every single show for the rest of that movie's performances at that location doesn't have various colored lines running through it. It only affects that ONE show. [Big Grin]

Posted by Monte L Fullmer (Member # 2797) on 05-11-2014, 12:37 AM:

On the BARCO: One of my 32B units decided to lose a rectifier this evening.

Got an error mentioning that lamp is lit, but one power supply is turned off.

Had to switch off CLO and go to Standard light output, then move the slider to not tax the other two rectifiers in the unit. Odd seeing a 65BA2 bulb only running 4100w due to the loss of that one rectifier.

Image on the screen looks okey, but a little bit dimmer, but to a layman, it was still watchable and like nothing occurred.

Called our tech department on this issue. Should get a PS sometime this week.

Fun things to look for.

-Monte

Posted by Carsten Kurz (Member # 5396) on 05-11-2014, 07:46 AM:

quote: Monte L Fullmer
Had to switch off CLO and go to Standard light output, then move the slider to not tax the other two rectifiers in the unit. Odd seeing a 65BA2 bulb only running 4100w due to the loss of that one rectifier.

Ooops. Didn't even know that operation mode was possible?

As to stuck pixel - TI has a pretty good history of long-term testing for their DMDs. While these are micromechanical devices, they have a surprising track record of NOT failing. So, while it does occur, it seems it is safe to assume it will not simply increase over time with equipment aging. It would indeed be a nightmare for the future of digital cinema if stuck pixel were a natural incidence of wear or aging of the machines. Stuck pixel also barely exist on home cinema or presentation dlp projectors. Just try to imagine how many of these individual mirrors TI produced to date... 100.000*3 DMDs in cinema machines alone, multiply by 2.000.000 to 3.000.000 micromirrors... per DMD.

I have seen red dot clusters on a fairly new machine. It was extremely annoying. It seems they typically occur more often on new installations and thus are covered by warranty most of the time. But they are not always a matter of a defect DMD, can also be bad contacts/signaling/memory defects.

Problem is that stuck pixels wil usually occur only on one of the three primary colours, and always 'full on'. Fully saturated Red, Green or Blue is naturally more visible than most typical film/wear artifacts.

- Carsten

Posted by Lyle Romer (Member # 1266) on 05-11-2014, 10:28 AM:

quote: Carsten Kurz
Stuck pixel also barely exist on home cinema or presentation dlp projectors.

I'm not sure how rare this phenomenon is. I had quite the star field on my DLP rear projection TV. There were dozens of stuck pixels. The website that I bought the replacement DMD chip from seemed to sell plenty of them. One day I'll get around to photographing the old DMD. At the correct angle, you can easily see the stuck pixels with the naked eye.

Posted by Steve Guttag (Member # 268) on 05-11-2014, 10:48 AM:

If the pixels could be stuck off...then I suspect they would be FAR less of an issue...that it is right for one to have an image with 2/3rds of the color on a pixel or completely black at all times but stuck on...becomes VERY hard to ignore over time.

I think there will be a market for those that can change out the DMDs AND get them aligned again. I've been around it being done and it isn't all that easy. To get everything aligned again, one has to work in 3 dimensions to get the height as well as the normal convergence aspects right again and it is best done on a jig but I could be done in the projector with enough trial and error.

Monte...no need to go out of CLO...the projector will NOT kill itself. Those power supplies will only go as high as they can run and stop. Note, ALL barco multi-supply projectors will do this...that is run on what is left to keep the show going. And you'll never have an easier time changing a supply either!

Posted by Jarod Reddig (Member # 6363) on 05-12-2014, 02:32 AM:

I had a stuck pixel on one of the first plasmas Ive owned that developed the 3rd or 4th year I had it. It was white in color. Ive also bought an LED LCD tv and out of the box it had a cluster of 3 stuck pixel so i returned it. Seems to happen across many different imageing technologies.

Posted by Carsten Kurz (Member # 5396) on 05-12-2014, 05:12 AM:

It was quite common on LCD monitors. Manufacturers needed to communicate a special policy on the number of defect pixel that would allow warranty claims.

Then some manufacturers came up with zero-dead-pixel-warranties.

But they still do occur.

- Carsten

Posted by Jarod Reddig (Member # 6363) on 05-12-2014, 02:18 PM:

Yes your right. I believe Vizio is one of the brands with the zero dead pixel warranty

Posted by Steve Kraus (Member # 476) on 05-12-2014, 02:45 PM:

Don't any of them offer a repair / exchange service where a functional light engine (or whatever component) goes out immediately and you pay for repairs to yours which then goes on the shelf for the next one.

OR you can get your own back but you have double the service labor to swap it back and have to pay for the loan.

Steve