Film-Tech Forum ARCHIVE: Xenon flicker /Reflector looks like liquid mercury

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Posted by Frank Angel (Member # 248) on 06-15-2004, 11:13 AM:

A very strange thing is happening in one of the Strong Super LumeX lamphouses. We are running 1600W bulbs (Osram I believe), and both bulbs are not even up to their rated life, yet one has exhibited a flickering, unstable arc that started almost unnoticeably but has grown to the point where the bulb has to be replaced. One flickering xenon wouldn't raise an eyebrow, but the replacement exhibited the same anomaly after about 500 hours.

The projectionist who replaced the bulb claims that the lamphouse is not venting properly and thus causing bulb failure. However, the exhaust stacks are pulling a goodly amount of air, with the large diameter lamphouse exit flu into ducting which does not reduce in size anywhere along the route. The exhaust is pulling so much air that it can hold a heavy piece of cardboard up against the vent. The vents are equidistant between the two machines which are only perhaps 30 or so inches apart. In other words, the air suction is identical to both lamphouses. AND this system has been working for 10 years with no heat problems with either machine. I mean its 1600w! How much air flow do you need? I would think the lamphouse fan alone would be adequate (which is operating normally, no dirt buildup, etc).

So I was quite skeptical about the cause of the bulbs early failures as being excessive heat. Both machines are cool to the touch; in fact, there was no particular difference between the "hot" house and the good one, either the lamphouse body or the projector gate itself. I didn't think heat could be the cause until I looked into the lamphouse at the mirror, only to find that a band, about four inches in width, approximately in the middle of the reflector circled it. This band looked like it was a dappled, rough surface rather than mirror smooth like the rest of the reflector. This banded part looked like what a piece of aluminum foil looks like if you were to crumple it up really tight and then unraveled it and try to make it flat again. That's what it looked like with the lamp cold. However, when the machine was running, I looked into the view window and could see that band of what has to be a damaged area of the reflector, was now shimmering, as if it were liquefied -- mercurial if you will. It no longer looked solid. Again, the lamphouse remained cold to the touch, the lamp electrodes didn't seem overly red and there didn't seem to be any visible bulb damage (like misshapen quartz bubbling at the metal/glass junctures). This sure looks like some kind of melting of the mirror surface, but nothing else seems amiss. In fact, even the picture, aside from the arc flickering, is as bright as the other machine.

Has anyone seen this kind of thing happen to a reflector? Now mind you, I have not seen it close up, only through the view window and then with the door only slightly opened because they didn't have protective gear and I was just peeking in threw a small slit of the slightly opened lamphouse door. Plus, I am not even sure if it is a cold reflector or not, although it doesn't seem to have that look, so my guess is that it isn't. I will know more when I can remove the bulb and inspect the reflector more closely.

Anyone have any ideas how it could be lack of heat removal when a robust exhaust system is going to both stacks literally inches away?

Power supplies are Strong switching rectifiers, 628000. One of them isn't exactly healthy -- the adjustment pot cannot bring the amperage up to more than 60 amps. And although that needs to be addressed, it isn't the pressing issue because that's the machine where everything has been working well since its installation.

Posted by Richard Fowler (Member # 893) on 06-15-2004, 11:41 AM:

Frank you have coating failure usually due to age, incorrect bulb placement, heat issues. Generally this appears as a band or streak. This will happen also to glass dichoric reflectors.

Posted by John Anastasio (Member # 607) on 06-15-2004, 05:53 PM:

The coating has actually lost its bond with the reflector and is sitting loose on it. When the lamp is off, static makes it cling to the glass. When it's hot and running, the coating is acting just like a really thin piece of foil...it expands and loses its grip a bit, then gets blown around by the air currents in the lamphouse. I saw this problem in a lamphouse I rebuilt once that had been heat damaged. When I touched the cool mirror surface with a piece of cloth, the silvering flaked right off and floated around the room like pixie dust.

Posted by Rick Long Jr (Member # 541) on 06-15-2004, 08:23 PM:

Not to be a goof, but have you cleaned the intake fans lately? the squirrel cage needs to be free of crud to effectively cool the reflector. It is unusual for this to happen with only 1600 watts, but if the reflectors are old...
I've had to replace a number of Super Lume-X reflectors that were running with 2500 watt bulbs, as after a couple of years, the coating flakes right off. Be carefull not to breathe the stuff in. It can't be good for you.

Posted by Paul G. Thompson (Member # 655) on 06-15-2004, 09:08 PM:

Rick is abslutely correct. Inspect those tumblers frequenty and clean them as needed.

Stuff a meat thermometer in the stack. If you read more than 120 degrees, you have a cooling problem.

Posted by Will Kutler (Member # 770) on 06-15-2004, 10:26 PM:

Definately clean the squirrel cages, and other areas, including the interiors of the duct-works!

Refering to the Christie lamphouses, there are also some lubrication points for various mechanical areas.

If you go to clean the Christie duct work, be careful, as the removal and installation can be a real pain!!

I always wondered...on the Christies...if it would be possible to cover the inlet duct with a home-made filter made out of a womans stocking or something, and compensating the loss of inlet air by adjusting the performance of the squirrel cage motor? An advantage might be improved dust collection and less dust in the lamphouse. A down side would be the constant checking and cleaning of the filter to prevent clogging and loss of inlet air, resulting in the lamp-house shutting down by lack of amount of available exhaust air causing the exhaust micro-switch to fall down...

Sorry about my illegible yap-yap...kinda tired and should have posted this later! [Big Grin]

Posted by Gordon McLeod (Member # 33) on 06-16-2004, 02:51 PM:

Often the mirror will flake in rings if the lamp was too far back in the reflector

Posted by Frank Angel (Member # 248) on 06-18-2004, 03:16 PM:

Thanks guys, I will be back in the booth tomorrow (SILENT RUNNING, again) and will check everything out thoroughly. I do clean the fans and the cages quite frequently and also always check the suction by putt my hand over the cage to be sure the thing is pulling air the way it should. Definately will do that thermometer test, Paul.

Thing is, from what you guys are saying, the flickering bulb and the reflector flaking could be totally unrelated. Or not heat related.

Will report back.

Posted by Frank Angel (Member # 248) on 06-23-2004, 05:42 PM:

OK, heat is ruled out. Both lamphouses are running cool -- no thermometer test yet, but unless there is some sort of weird heat inversions keeping a high temp around the reflector and yet allowing air flow to keep the rest of the lamphouse cool, then I am ruling out heat as the cause of the reflector surface failure.

As for the lamp flicker, again, I am ruling out overheating and will look to the rectifier as the possible source to see if the ripple is within tolerances. I was figuring the best way to determine if ripple is the problem would be to look at the DC on the "good" rectifier on an oscilliscope and see if the suspect unit shows anything different. Any suggestions for how to directly read a real ripple value and what would the acceptable level of ripple be?

Any idea what would be the cost of the reflector? Since the light output hasn't been affected so far, I am thinking of leaving the unit in until it fails (I learned that from Lt. Poole in 2001). If the flakey mercury stuff eventually comes off, I'll replace it. Then that would pretty much be it for the HAL-9000, wouldn't it? [Smile]