Film-Tech Forum ARCHIVE: Transformer's dying...HELP!!! SOS!!!

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Posted by Zach McQuaid (Member # 613) on 09-13-2000, 11:58 PM:

In our largest Aud. our projectors X-former is "tuna-factorying" itself (adj. To can, or to die out unexpectedly.) Why it does hum so bad? And flicker too real bad? What if I said fix it / or replace it? Which one?

Posted by Russ Kress (Member # 461) on 09-14-2000, 12:16 AM:

I'm assuming here that you are refering to the xenon power supply.

Call your tech.

We wire all of our power supplies with identical control connectors and welding connectors for the DC output.

Suggest this to him (or her) when they get there.

It changes a semi-complicated replacement into a quick swap.

Russ

Posted by Nick Perry (Member # 361) on 09-14-2000, 12:52 AM:

Could be diodes on the way out and/or need a tune.

Nick

Posted by John Pytlak (Member # 331) on 09-14-2000, 06:20 AM:

Hard to tell without more information. But if it is a 3-phase line into a "brute force" power supply, be sure all three legs are live and balanced (equal voltage readings relative to ground or between legs, while under load).

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

Posted by Mark Gulbrandsen (Member # 72) on 09-14-2000, 06:42 AM:

Would need to know what type it is but a couple off things that come to mind are loose windings on the iron core. Older Strong and Kneisley units do this sometimes. This can usually be eliminated by hammering thin oak wedges in between one side of the windings and the iron core. This sometimes requires disassembley of the entire rectifier though as in a 2kw unit. If it is an Irem unit there are adjustments via brass screws for the clearance of the variable core....to keep it from vibrating. Another thing possible is a shorted diode and a main breaker thats not sized correctly. The main transformer will just sit and and buzz, and bake(a dangerous situation!). Hope some of this helps out.
Mark

Posted by Mark Huff (Member # 480) on 09-14-2000, 08:36 AM:

Zach,

Looking at the location of Erie you must work for Cinemark. If this is so you have a Rentec piece of junk. We have a Rentec lamphouse doing the same thing. My engineer told me that they sometimes buzz like that but will last for a long time. When I requested what to do to fix it, he replied you have to get a new one and that would only happen if the one you have goes out. Maybe you have a different problem but I believe its the same thing. Call you engineer and let them know what the problem is. But before you do that like the others said check the diodes first.

Posted by Gordon McLeod (Member # 33) on 09-14-2000, 10:02 AM:

Probably a DIODE shorted and that is why it a flickers as one pahse is missing
and the niose is the transformer for that phase shorted out

Posted by John Walsh (Member # 168) on 09-14-2000, 10:41 AM:

I would agree; we need a little more information here...

At one theater, we had a IREM rectifer that hummed like crazy. But, nothing ever went wrong with it. Patrons could hear it out in the theater. We tried adjusting the laminations, but no-go. Finally, we just got rid of it.

At another theater, (again, an IREM rectifer) a diode shorted and caused a flicker on screen. It looked exactly on screen as if you slowed the projector to 12fps or so. The funny thing was, if you looked at the lamp itself, the light looked fine. You could not see any flicker at all. I'm guessing that the diode being shorted (rather than going "open") kept the caps from having any storage effect, and the light would only come on when the other phases were on.

I had thought that if the current to the bulb was shut off, however breifly, it had to be ignited to come on again. But it turns out that if the current is cycled quick enough, (only one phase missing) it will just come back on.

Posted by John Pytlak (Member # 331) on 09-14-2000, 12:49 PM:

The AC ripple that occurs when running with one phase out will dramatically shorten the life of the xenon lamp electrodes.

The "flicker" usually cannot be seen on the light output of the lamp directly, as it is still 60 Hz. (in Erie PA). But that 60 Hz current ripple "beats" with the 48 Hz. shutter frequency to produce a very noticable 12 Hz. flicker (60 - 48 = 12)on the screen.

Posted by Zach McQuaid (Member # 613) on 09-14-2000, 02:28 PM:

MARK: Correct, I do in fact work for C---m--- Movies 17 in Erie. I have indeed checked the diodes, they have even been all replaced. We must have the same tech if you also work for C---m---, because he told me the same damn thing. We have also adjusted all the tap settings on the stupid thing and yet it still hums like someone just fell into a tumbler.

The bulb is on it's way out with only 500 hours.

Posted by Aaron Sisemore (Member # 145) on 09-14-2000, 03:25 PM:

Check the current while the lamp is lit, if it is a dead phase or one shorted diode not only will you get the 12hz flickering, the current should drop to 2/3 the normal current, and may or may not fluctuate with any arc unsteadiness.

Usually a shorted diode will not allow the lamp to even operate (loud buzz and the transformers will start smoking if left on and the breaker doesn't trip), but sometimes an open diode will cause the 12hz flickering and allow the lamp to run at reduced current.

Aaron

Posted by Nick Perry (Member # 361) on 09-16-2000, 02:05 AM:

What color are the coils? Are they a dark brown or a light copper color? Have you been running the rectifier slightly over it's rated maximum current?

Nick.

Posted by Don Olson (Member # 90) on 09-22-2000, 12:21 PM:

Can't comment on the flickering. Not enough info. But....driving wooden wedges into transformers is dangerous. When working as an independent tech you may end up buying a transformer for the customer. I am no longer a "master of disaster" ( chain tech ) but in the past I have fixed noisy transformers by spraying motor winding insulating varnish into the cracks and gaps. Many applications. Let it dry and re-apply. A couple cans. Mask off what you don't want to get it on. Lay the rectifier on its side to get it to flow into the cracks if necessary. Grainger carries the stuff. Good luck and use good judgement.

Don Olson Component Engineering.