Film-Tech Forum ARCHIVE: Floating bulb focal point

This is topic Floating bulb focal point in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Dan Chilton (Member # 2288) on 11-18-2006, 05:05 PM:

This is a tough problem to explain, but here goes: About a week ago, I noticed that the top right portion of the screen was going from bright to a little dim in a pulsating fashion... yet with no apparent pattern or frequency. I told my tech about it, and he had me switch the voltage (or something to that degree) in the rectifier. Didn't fix it. When I tried refocusing the bulb, I noticed something odd.

Imagine the bulb being focused so tightly that you have a nice sharp circle of light, with a less bright halo around the perimeter. When I focused the bulb to this degree, I noticed that the sharp circle of light was floating around, almost like the light produced from a candle flame. That's the best way to describe it. There's no rhyme or reason the movement. It's not effected by motor vibration, or ventilation... it just kind of moves around at will.

Any idea what would cause this? The lamphouse is properly ventilated, the bulb has less than 300 hours on it... ??? [Confused]

Posted by Dennis Benjamin (Member # 1137) on 11-18-2006, 05:11 PM:

...change the bulb.....

Seriously. If you have to - switch it with another projector's bulb (if they are the same size). Find out whether it is the bulb thats the problem - or something else. If you discover that the bulb is the problem (and not something else). You can send it back, most bulbs are under warranty way past 300 hours.

The problem is: it could be one of numerous things. You have to identify what the problem is by process of elimination.

Good Luck.

Posted by Dan Chilton (Member # 2288) on 11-18-2006, 05:35 PM:

I checked out the report on bulb failure under the tips section, and I think it might be that the rectifier isn't filtering out the electrical ripple. My tech says the capacitors might be dried up, which would cause that. If it worsens, I'll switch out rectifiers and see if that changes anything.

BTW, I already switched bulbs and the problem persists.

Posted by Louis Bornwasser (Member # 3063) on 11-18-2006, 10:26 PM:

Is there a magnet located under the reflector? On Super Lumex these are OPTIONS. What bulb are you using? Osram 2000 watt require magnetic stabilization; weird foreign bulb flicker normally. Louis

Posted by Richard May (Member # 2627) on 11-20-2006, 04:13 PM:

What rectifier and lamphouse are you using?

Posted by Bernie Anderson Jr (Member # 410) on 11-25-2006, 10:03 PM:

If you're getting a flicker that is random, its an unsteady arch. If the flicker is strobing, that is AC leaking into the bulb. That would be either a diode that is open for starting to fail, maybe a bad filter cap. To be honest, I've never seen a filter cap go in a projector that is used every day. I've seen it in rectifiers that have been sitting unused for years. Change the bulb if there are high hours on it. If the bulb is around 1000 hours, rotate it 180 degrees and raise the amps up 5 more amps. Multiple the voltage and the amperage which equals the wattage. Never go past 110% the rated wattage.