Film-Tech Forum ARCHIVE: Projection Light Flicker

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Posted by Geoffrey Rau (Member # 3445) on 11-07-2005, 10:24 AM:

At one of my locations we have been having trouble with the projection light continually flickering on screen. We have changed out the ignitor and the power supply with no success. The bulb life has been cut down to less than 350 hours of "good" light. Any ideas?

Posted by Leo Enticknap (Member # 534) on 11-07-2005, 10:37 AM:

I'm assuming that the problem here is unsteady light output from the bulb, rather than a shutter issue, given your reference to the life of each bulb.

I had a similar problem towards the end of my time as a projectionist. A lamphouse was frying bulbs after around 700-900 hours ish (one of which blew up), and we assumed it had to be a fault in that lamphouse/rectifier combination. The same model of bulb in the same model of lamphouse in other projectors in the same theatre was lasting for well over 2k hours, with regular rotation, before any degradation of the light output became visible.

After much head scratching, it eventually turned out that the ammeter shunt was the wrong sort, thereby causing the ammeter to give the wrong reading. So we thought we were running the bulb at 65 amps or thereabouts, whereas in fact it was probably running at well over 100.

The picture looked nice and bright, though! [evil]

Posted by Monte L Fullmer (Member # 2797) on 11-07-2005, 01:11 PM:

Welcome to Film-Tech! We can help!

Go into your breaker panel that runs the rectifier, and I bet that you're running a 3phase rectifier and one leg has opened up, or you have one breaker that died in that triple, causing the one phase not to run the rectifier evenly, thus flicker due to the bulb is pulsating, but to the naked eye you don't see the flicker.

But with the shutter swinging around causing a pulsing effect in iself, the light pulse from the bulb is going out of sync with the shutter causing this flicker on the screen.

good luck-Monte

Posted by Brad Miller (Member # 2) on 11-07-2005, 03:16 PM:

He said the bulb life has been cut down to 350 hours, which tends to make me think that the quality of the light is ok for the first 350 hours, thus ruling out the loss of a leg of power. It also rules out an open diode or a hole in the shutter.

Sounds to me like the bulb is being overdriven, possibly with low exhaust and he is killing the bulbs. Leo pretty much covered it above.

Geoffrey, We need to know what brand of bulbs, the size of the bulb, the make and model of the lamphouse, and what the meter "says" it is running at on the side of the lamphouse to really be able to troubleshoot much farther. Always try and give as much information about a problem in your initial post It will help save a lot of time chasing around false ideas.

Posted by Steve Guttag (Member # 268) on 11-07-2005, 04:41 PM:

Don't forget to note the projection angle...very steep projection will put a hurting on a xenon lamp...as will improper stabilization magnet.

What is the condition of the lamp when it comes out...is the envelope clear or very dark (a dark evelope is a tell-tale sign of over current, like Leo's...just ran across an ammeter that was off by 22A).

Look at the anode...is is more or less clean or does it look like there are mountains and craters on it...indicating poor electrical power.

Posted by Gordon McLeod (Member # 33) on 11-07-2005, 08:14 PM:

Also has the magnet been misaligned

Posted by Monte L Fullmer (Member # 2797) on 11-07-2005, 11:53 PM:

quote: Steve Guttag
is is more or less clean or does it look like there are mountains and craters on it...indicating poor electrical power.

Steve, could you please define "poor electrical power" - would this be "dirty power" and if so, how can one rectify this problem. I get bulbs (2k) which, I'm sure this is a normal run, with advanced bulb age that have these "mountains and craters" on the face of the anode. But some age quicker than others even everything in my power is good (power, exhaust and tight connections..)in order.

thx-Monte

Posted by Steve Guttag (Member # 268) on 11-08-2005, 05:25 AM:

Any form of AC will cause these problems. If you have large lumpy things on your anode, try changing the main filter capacitor, that normally will solve the problem providing that your AC input is all in order (well balanced legs).

Most people don't seem to realize that electrolytics have a limited shelf life and use life...ever notice the date code on them? If they are 10+ years older, change them on inspection.

Posted by Brad Allen (Member # 470) on 11-11-2005, 06:56 PM:

What is the proper way to check the alignment of a magnetic setup?
Kneisley Xenex 1 lamphouse's.

Posted by Steve Guttag (Member # 268) on 11-11-2005, 07:58 PM:

With a welding mask and gloves...the arc should be centered on the anode...adjust the magnet up to bring the arc down, and vice-versa. Keep as much of your body covered while the lamp is lit to avoid excessive UV radiation giving you one heck of a sun-burn.

Posted by Brad Allen (Member # 470) on 11-14-2005, 12:57 PM:

Thanks,

Another question. What's the purpose of having a "chain" hanging off of a xenon bulb?

Posted by Fabrice Dubourg (Member # 1635) on 11-14-2005, 03:40 PM:

1 phase lost on the line from the breaker to the rectifier.

Posted by Bob Brown (Member # 1205) on 11-14-2005, 08:41 PM:

Interesting topic....We have been battling the vary same thing at my theatre. Is there any special breaker that I could use other than the normal run of the mill, 3-phase breaker. I am experiencing the same short lamp life and flicker. We are using 7k OSRAM lamps. We have checked the exhaust flow, checked out OK. We are also using modified Miller rectifiers. For the ones in the know, you will be able to figure out what kind of system I am talking about. But, any ideas would be most welcome.

Posted by Daryl C. W. O'Shea (Member # 1303) on 11-14-2005, 11:36 PM:

If you're using the breaker as a switch, you'll have better luck with a disconnect box. Of course, it'd take a blind man not to notice an open leg, and even non switch rated breakers should have a decent life span.

Posted by Monte L Fullmer (Member # 2797) on 11-14-2005, 11:56 PM:

quote: Bob Brown
I am experiencing the same short lamp life and flicker. We are using 7k OSRAM lamps

..read Steve's topic above, for your rectifier might be getting tired and need the caps replaced since they can't control the DC voltage ripple very well as if they were new.

Osrams..switch to Christie for better bulb results...

-Monte

Posted by Gordon McLeod (Member # 33) on 11-15-2005, 07:46 AM:

Christie is not to my knowledge on the approved list of lamps for your system

Posted by Daryl C. W. O'Shea (Member # 1303) on 11-15-2005, 11:37 AM:

If I recall correctly, SQP lamps are though.