Film-Tech Forum ARCHIVE: Bulb Flicker

This is topic Bulb Flicker in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=011213

Posted by Tom Wienholt (Member # 1510) on 04-13-2012, 02:32 PM:

I have an Optimax Theatre Console model CV2000. I recently started to notice that the bulb is flickering. This can clearly be seen through the small "view port" on the console. I decided to replace the bulb (Christie CXL-20R) even though it only had about 900 hours on it, and the new bulb still flickers the same way. After doing some forum searches, the filter capacitors in the rectifier were discussed as a possible cause. So, I replaced the caps with new ones and the problem still persists. What else could be causing the issue? Any help would be greatly appreciated. Thanks.

Posted by Victor Liorentas (Member # 5272) on 04-13-2012, 02:43 PM:

I would think the diodes are causing it? If the light pulses then bad diodes are the culprit.Perhaps... although the bulb may not be getting enough cooling during it's life?
At what point does it start to flicker in hours?

Posted by Monte L Fullmer (Member # 2797) on 04-13-2012, 04:05 PM:

If one bulb does this early flicker, I would call it a defective bulb in itself, but if all bulbs during the lifetime of the lamphouse flickered at an early age, I'd be pointing to cooling, or rectifier filtering.

For flickering is when you basically get the buildup of pointed tungsten on the end of anode, in which I call "Ripple Horns", and this is basically caused by high pulsating ripple in the DC current feed.

What amperage amps is the bulb ran at - between 70 an 80amps? Any higher or lower amp settings taxes the life out the bulb drastically.

Is the rectifier a single phase, or three phase rectifier?

-Monte

Posted by Tom Wienholt (Member # 1510) on 04-13-2012, 05:01 PM:

I am running the bulb at 78amps. It is a 3-phase rectifier. The flickering became noticeable around 700 hours on the first bulb in question. But, after a brand new bulb was installed flickering continued. I then replaced both filter capacitors and the problem persists.

Posted by Monte L Fullmer (Member # 2797) on 04-13-2012, 06:20 PM:

Is it a diode rectifier, or a switcher rectifier?

If diode, wonder if you got a pair of diodes that are not doing their thing, or one transformer isn't getting the correct secondary voltage to its respective pair of diodes.

Posted by Tom Wienholt (Member # 1510) on 04-13-2012, 08:43 PM:

It's a diode rectifier. But, is it even possible that it is a bad diode? My experience with bad diodes is a "strobe" effect, not a flicker.

Posted by Randy Stankey (Member # 64) on 04-13-2012, 08:51 PM:

It's the diodes. One or more of them is leaking.

This problem will eventually get worse and worse until one of those diodes will fail and you will lose a show.

Change them now and save yourself a lot of trouble later on.

Diodes are like light bulbs. Some last longer than others. Some seem to last forever. Others don't last long at all but, eventually, if you use them enough, virtually all of them will fail.

Yes, you can buy better (more expensive) diodes that will last longer. You can do other things to the rectifier to help diodes last longer. Some people say that they never change diodes.

However, the bottom line, no matter how you slice it, diodes are replaceable parts.

You should always have at least one set of spares on hand for each type of diode used in your theater.

Posted by Louis Bornwasser (Member # 3063) on 04-13-2012, 08:58 PM:

All of the above is true. You could also have a bad leg on the 3 phase, either the breaker, the wire, or the contactor. Louis

Posted by Tom Wienholt (Member # 1510) on 04-13-2012, 09:06 PM:

Ok thanks. Does anyone know of an online source and part# where I can buy diodes? I would prefer to "beef" them up.

Posted by James Giesen (Member # 6858) on 04-14-2012, 05:28 AM:

I was just going to say about a Phase problem But Louis beat me to it.
We get this problem regulary with our great town power supply.

Posted by Randy Stankey (Member # 64) on 04-14-2012, 08:51 AM:

I'll agree with that. [Smile]

However, I would say that checking the diodes to see whether they are good or bad would be a lot easier than tearing the contactor apart to see if the contacts are burned.

If the diodes are good and the problem still persists, follow through the rest of the things.

If the contacts are bad, you can take a piece of emery cloth and clean them but this should be seen as only a temporary measure. I think most electrical contacts have a coating on them to prevent corrosion from just this sort of thing. If this coating gets worn away, the contacts will corrode again, this time much faster.

So, you can clean the contacts to get the projector running again but you also need to order a new contactor or a new set of contacts to go in the contactor. Either way, there's replacement needed.

I still think checking the diodes and/or replacing them should be the first step you take. Tearing out a contactor can be a pain in the ass.

Always try the easy things first. [Wink]

Posted by Dave Macaulay (Member # 813) on 04-14-2012, 11:16 AM:

Most contactors have fairly large solid silver contacts. Dressing them with a file or emery cloth will get them back in operation for a long time. Usually replacement contacts are available, some common rectifier contactors are actually 4 pole, with the fourth pole for auxiliary power or unused: these contacts can be swapped with a high current set that's burnt a bit.
Diode or contactor failure usually shows up as slightly visible or unnoticeable flicker with the projector stopped open shutter, and a pronounced slow flicker with the projector running as the 60hz lamp flicker goes through the 48hz shutter. It doesn't usually cause usually what you see as flame movement through the viewing window, until the lamp is damaged from high ripple: this creates odd bumps on the lamp electrodes and the arc jumps around between them.
If you've lost a phase I think the filter capacitor lead wires will have melted from high current, that's pretty normal. One diode doesn't seem to do this but an open diode pair or lost phase does.
Check your lamp current with a different amp meter, clamp on ones are easiest. The console meter may be way off and you're running over or under the rated current for your lamp.

Posted by Randy Stankey (Member # 64) on 04-14-2012, 01:16 PM:

I have no doubt about what you said but I have not seen silver contacts. All of the ones I worked on were gold colored with some kind of hard plating on them. I could dress them but, once that plating is gone, they wore out a lot quicker.

One the few occasions when it happened to me, I dressed them then ordered a new set of contacts or a whole new contactor. Then, on my next visit to that theater, I would replace them.

Silver contacts would have been much nicer.

Posted by Tom Wienholt (Member # 1510) on 04-14-2012, 02:50 PM:

When I replaced the capacitors, I noticed that there is something that bridges the two terminals together on each capacitor. Is this a resistor of some sort? Could this need replacing as well?

Posted by Monte L Fullmer (Member # 2797) on 04-14-2012, 03:17 PM:

Those are bleeder resistors to take the charge out of the caps when the unit is powered down.

If those resistors weren't on there, those caps would keep holding their charge and hate to see you touch something across a charged cap - to hear results of your findings.

Posted by Dominic Espinosa (Member # 2122) on 04-14-2012, 08:11 PM:

quote: Tom Wienholt
Does anyone know of an online source and part# where I can buy diodes? I would prefer to "beef" them up.

I've had moderate success with grainger and mouser lately for a few bits and pieces like this.