Film-Tech Forum ARCHIVE: Flickering Image On Screen Once Motor Is Turned On

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Posted by Aaron Mehocic (Member # 15) on 04-20-2004, 07:11 PM:

This problem might be a simple overlook on my part but I need help in the diagnosis. I'm running a Kneisley Xenex II 3000 watt lamphouse with a Kni-Tron rectifier which by themselves are working normal. However, once the projector motor is turned on I've got a bad flicker in the image on the screen. Saturday night, the threephase breaker was tripped about four times, but has since settled down and cooperated. Since then the bulb is functioning on 85 amps instead of the rated 95. The rectifier was checked and compared with a perfectly functioning model of the same type and found to be just fine. The shutter was even checked for damage and realigned, though I did not think that would stop the flickering problem. Is it possible the motor to soundhead belt is worn out and needing replaced? (Simplex models) Any help would be appreciated thanks.

Posted by Mark Gulbrandsen (Member # 72) on 04-20-2004, 07:38 PM:

I have literally worked with hundreds of Kneisley rectifiers and lamphouses...actually even today at a Drive Inn in north central Wyoming which had a 4K conversion inside an old Strong Excellite 135! IN this case the threaded negative CXL adaptor had welded itself onto the bulb. I feel that you have a low phase in the rectifier so check CARFULLY the contactor and related AC wiring for burnt up stuff. This is fairly common in Kneisley stuff. If you find the rectifiers AC components o be ok then go back to the panel, or sub panel and carefully check there, but the best place to start in a Kneisley is at the contactor...measure the in and out sides to be sure the contacts inside have not burn't up. The low phase is causing some excess ripple on the DC which cannot be filtered out easily.
The other possibility is that a diode has failed(open) and the ripple has gotten very high.... a good clue there is that your breaker now stays set. Disconnect all of the braided lead ends of the diodes and check them thet way.
Mark

Posted by Brad Miller (Member # 2) on 04-21-2004, 03:07 AM:

Since you lost amperage and said the flicker is only present when the projector is running, my money goes on one open diode in the set.

Posted by Aaron Mehocic (Member # 15) on 04-24-2004, 01:49 PM:

Thanks for your advice...it was a diode. The Kni-tron rectifier is, in my opinion, one of the better pieces of equipment out there and from what I've been told, diode problems are something that is more the exception than the rule. Once again you guys came through!

Posted by Mark Gulbrandsen (Member # 72) on 04-24-2004, 02:54 PM:

The Kneisleys are ok rectifiers and provide VERY clean DC, especially the single phase units. There are downsides to them though.... because of the design of the transformer they draw huge amounts of current per phase compared to most other rectifiers, the fibre board that all the connections mount to can be a problem as the material used has a tendency to suffer from compression set causing connections to loosen up and then burn up. Transformer windings can also fail and catch fire... I've seen this happen.

Mark

Posted by Aaron Sisemore (Member # 145) on 04-25-2004, 09:53 PM:

quote: Mark Gulbrandsen
the fibre board that all the connections mount to can be a problem as the material used has a tendency to suffer from compression set causing connections to loosen up and then burn up. Transformer windings can also fail and catch fire... I've seen this happen.

Odd, I have only seen those things happen to older Christie power supplies. [Roll Eyes]

-Aaron

Posted by Mark Gulbrandsen (Member # 72) on 04-26-2004, 10:01 AM:

Yea, have seen that in Christies too. On normal scheduled service I always check this stuff but many theatres don't have norlmal scheduled service.......
Mark