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Author
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Topic: Xenon flicker /Reflector looks like liquid mercury
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Frank Angel
Film God
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Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 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.
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