Brightness issues

[Mark Gulbrandsen]

I had to replace a cracked light pipe on an NC-900 a long time ago when lamp explosions were almost a weekly occurrence. The one I had to replace had a chip out of the tip and resulted in the problem you are describing here. Note that I have never found glass shards anywhere but in the lamp compartments in an NC-900. Assuming that both lamps are good, and that one lamp does not have a lot more "ON" hours on it than the other (which can also cause this issue) then run each lamp independently at 350 watts and measure your light output and see what each lamp produces. You can also switch lamp positions and reset each to the same 350 watts and see if the problem follows the lamp or it the problem stays in that lamp position. When setting power give it ten minutes to stabilize!! Also, it your projector 4 is near the popcorn popper then it may be that you have taken in a lot of grease and the optical path needs cleaning, I had that happen on a Christie a number of years back. Also, In this projector, when you install new lamps, it is always best to change both a the same time.

[Steve Guttag]

Don't discount the heat. The lightpipes can/do get VERY hot. The higher you run your lamps, the more clogged your filters are, the hotter that thing gets, the greater the likelihood that you crack on/both pipes. Make sure that projector has adequate cool air as a source and that your filters are clean so that proper air flow can be established. I've had sites that never had to change a lamp before warranty and they are the ones that have the lowest ambient temps and keep their filters changed. Note, when NEC evaluates a warranty claim on a lamp, they always want a 2-year copy of the logs. One of the key things they look at is the inlet temperature.

[Carsten Kurz]

Armand - getting a tech in to analyse this issue across all projectors could become expensive, if they follow their usual approach (e.g. first dismantling the projector to find light-pipe/combiner issues).
These NC900 are the worst to service mechanically, they are crammed.

Basically, you should be able to diagnose it yourself - until the point where it becomes clear that there is an actual defect and a repair would be necessary. You need a wallplug-powermeter, and you mention you have a light meter. That light meter, though, could be the greatest source of misleading measurements, since you need to have a good understanding of what you actually measure. Please describe the type of meter (picture), and tell us how you use it. Switching bulbs between slots/projectors and measuring power consumption and illuminance should give you a good indication what the problem is and which projectors are affected.

[Mark Gulbrandsen]

Don't discount the heat. The lightpipes can/do get VERY hot. The higher you run your lamps, the more clogged your filters are, the hotter that thing gets

Light pipes are designed too get VERY hot. Its the lamp explosions that used to damage them, Temperature monitoring is one of the great features of NEC. Lots of temperature sensing and you can not over heat a projector in almost any aspect, even if you try.. I did when we got the first NC-900 in for Demo quite a few years back. We built a box over it to simulate heat buildup and air intake cut off. The lamps get too hot and the ballasts are shut down by the on board CPU. Same for the .internal operating temp of the projector, as well as the card cage electronics, the ICP has it's own temperature sensing of critical components.. If you covered it as we did, and tried to smother it the projector would merely go into Standby. The NC-1200 and 2000 do exactly the same thing and once it shuts down it requires a reboot and cooling down period before it can be used again. .

BTW, I had a Christie CP-2000 get a cracked light pipe from a 6KW lamp explosion once. It took out the Dolby 3-D filter wheel and the light pipe was shattered internally resulting in splotchy light on screen. Nothing temperature related on that one though.

[Steve Guttag]

Okay Mark...I'm sure your testing was extensive and over a long period of time (months). NC900s and cracked light pipes are not too uncommon and lamp failure due to excessive inlet temps are also common...in fact, it was in an NEC class that it was discussed.

The NC900 is probably the least able to dissipate its heat on the light pipe. If you want to adjust it, you have to do it very fast as it will seize up shortly after the lamps are turned on due to the metal expanding.

[Mark Gulbrandsen]

Okay Mark...I'm sure your testing was extensive and over a long period of time (months). NC900s and cracked light pipes are not too uncommon and lamp failure due to excessive inlet temps are also common...in fact, it was in an NEC class that it was discussed.

On 34 NC-900 that have been installed since early 2103, so years and many projectors in different locations. Those include 4 of the very first ones that came into the country. They are scattered all over too, and only one light pipe has had to be replaced. My biggest beef about the projector is having to send light engines back overseas for cleaning.

[Steve Guttag]

Okay...so about a 3% failure rate on the light pipe then. I'm up to zero light pipes but I have a friend that has changed several. I come back to NEC themselves claiming that it is very important to keep the ambient temperature low enough and the filters clean enough for it to cool itself.

[Mark Gulbrandsen]

I'm up to zero light pipes but I have a friend that has changed several.

Zero out of how many NC-900? The only other issues I had were two lens mount positioning wires shorting (fixed on site) and one failed ballast... also from a lamp explosion. I never blamed NEC for the explosion issue, that was a Ushio problem. They blew up in the Sony projectors too. Overall I would never be able to stay in business if I were to depend on just repairing NEC projectors.

[Marcel Birgelen]

On 34 NC-900 that have been installed since early 2103, so years and many projectors in different locations.

Hey, Doc., before you jump into that flying Delorean, can you give us a hint how long we'll have to cope with this corona thing you may have read about in history books?

[Leo Enticknap]

Another vote for one of the light pipe components (either the integrator rod itself, or a mirror or lens element within the pipe).

I once had an NC2500 that was reported as suddenly losing light for no apparent reason. The end user reported that until about 18 months prior, they had been using 4kW bulbs. Then they had to go up to a 6 to maintain acceptable light on the screen, then 7. Finally, even 7 wasn't enough. After exhausting everything else in the light path, it turned out that the integrator rod had, err, disintegrated.

[Armand Daiguillon]

After hours and hours of testing there is only one projector that may have the pipe issue (its dim no matter what bulbs I put in) - the rest of the projectors seem to be pretty consistent in the results.

Since I took over this theater we replaced 3 bulbs, and of the 10 bulbs we tested, 3 produced light levels significantly better than the others. Older bulbs with god knows how many hours were outputting 15-20 lux. The newer bulbs were outputting 50-60 lux. Since I know that we replaced three, and three of ten are showing similar results - I think its safe to say that the dim bulbs have been run way too long. I just never expected performance to deteriorate that much at end of life.

Thank you all for your input !!!

[Carsten Kurz]

Armand - are you able to set light levels on these units yourself, do you know how to do it?

Lux is not a dependable number - admittedly, if you 'feel' that an image is much too dim, it may still be an indicator.
That's why I asked what type of light meter you are using and how. Before you can compare measurements with an illuminance meter like this, you need to under stand what you measure. Simply holding such a meter into the light path will not give you a useful reading.

[Marcel Birgelen]

If every projector has the same lens and every room has exactly the same screen and every projector is zoomed to the same level and you measure it at the exact same distance in every room, the reading will give you a somewhat useful comparison between the rooms.

Another vote for one of the light pipe components (either the integrator rod itself, or a mirror or lens element within the pipe).

I once had an NC2500 that was reported as suddenly losing light for no apparent reason. The end user reported that until about 18 months prior, they had been using 4kW bulbs. Then they had to go up to a 6 to maintain acceptable light on the screen, then 7. Finally, even 7 wasn't enough. After exhausting everything else in the light path, it turned out that the integrator rod had, err, disintegrated.

I'm still looking for the perfect English translation for the German word "Sollbruchstelle", "disintegrator rod" is a close, but somewhat too specific candidate.

[Mark Gulbrandsen]

Hey, Doc., before you jump into that flying Delorean, can you give us a hint how long we'll have to cope with this corona thing you may have read about in history books?

Watched 60 minutes last night and they interviewed an Air Force General about exactly that. He suggested that things will never get back to the normal we once knew. Makes me glad that I am 89% retired!! Enjoy the fun and chaos! My personal feeling is it's going to take a minimum of around five years. Once they develop a vaccine, it's going to take years to get a sufficient number of the world's population treated against it.Similar to how long it took to eradicate Polio.
The good thing is it makes a HUGE case for Medicare For All.

I think its safe to say that the dim bulbs have been run way too long. I just never expected performance to deteriorate that much at end of life.

Again, we really don't know what size your screens are or what gain the screen surface is and condition... 1.0, 1.2, 1.4, gain, etc. NEC specifies their light levels on a 1.4 gain white screen. It has been my experience that you don't want to spec the NC-900 on a screen where the lamps start out at more than 66 to 65 percent of maximum. When the lamps reach about 2000 hours (They have 3000 hours warranty) you will see a 15 to 20 percent drop in brightness if all is normal. So you need some head room to turn the lamp power up a bit to keep it as close to spec as you can till the lamp life goes ding. Also, when you remove a lamp, label the box as to how many hours it has on it at removal. If you make it to 3000 hours and have the power near 100% and the image is still too dim then the projector was not properly sized to the room and screen.

[Carsten Kurz]

disintegrator notch comes even closer