Film-Tech Forum ARCHIVE: Picture flicker on Christies

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Posted by Frank Dubrois (Member # 3042) on 03-28-2007, 11:07 PM:

Our picture flickers. It almost looks like the shutter is slightly out of time, however, it is not. I not only replaced the entire assemblie, but retimed it as well. A brand new bulb was put in, however, nothing has changed. There was a somewhat large amount of dirt (belt dust, leaking bearings = mess) on the inside of the projector, but nothing really seemed out of place. The shutter belt was worn down a bit and replaced. So why is this still flickering? Could it possibly be a diode? Usually if its a diode, the flicker is much more pronounced, this is bad, but not horrible. Bright white scenes are intolerable for ME to watch, however, we have not received any complaints.

Posted by Monte L Fullmer (Member # 2797) on 03-29-2007, 12:42 AM:

Bulb is focued in too close to the trap and gate. Back the bulb off a bit.

quote: Frank Dubrois
Bright white scenes are intolerable for ME to watch

..this was the first clue that tipped this off.

Posted by Dustin Mitchell (Member # 372) on 03-29-2007, 01:13 AM:

Actually it sounds like a diode problem.

Posted by Brad Miller (Member # 2) on 03-29-2007, 02:21 AM:

If it is a diode, the picture will be fairly dim and the flicker to a ridiculous level.

I'm with Monte on this one, the bulb is probably not focused properly. Are the bright scenes REALLY BRIGHT? If so, that's your problem. The bulb needs to be focused properly.

Of course those Christie lamphouses DO put off one hell of a lot of light, so maybe you will want to swap that out with a Strong or something. [Razz]

Posted by Alex Grueneberg (Member # 2652) on 03-29-2007, 03:47 AM:

I've noticed a few houses like that here and the bulbs are focused properly (trust me). How common is it for the diodes on these to fail, and do they ware down over time? Or is it simply, it lights or it doesn't. As an example lets say i have a 7 year old SLC with more then likely original diodes with 2k in a 100 seat house. The shutter is correctly timed as well. Any light (white) looks like a slight subtle strobe effect in the light output and really bothers me but since customers don't complain no one else cares.

Posted by Frank Dubrois (Member # 3042) on 03-29-2007, 06:43 AM:

Alex, that sounds like the issue I have. I've had a SLC lamphouse that had a bad diode where the lamp lit, but the flicker was ridiculously obvious. It was almost like a blinking rather than a stobe. I will check on the bulb issue and see if that solves it, if not, then back to the drawing board.

Posted by Ian Woloschin (Member # 3709) on 03-29-2007, 06:44 AM:

I've noticed similar problems with my two DP-70s with Christie lamphouses (with 3K bulbs). I kept noticing a strange flicker, but no one ever complained, and other people in the booth seemed to not notice it until I pointed it out.

I had a technician come in to fix some other problems we were having and asked him to look at the flicker. Unfortunately, someone else was covering for me in the booth when they checked out the flicker problem, and neither of them were able to really see the flicker or notice any problems.

Posted by Louis Bornwasser (Member # 3063) on 03-29-2007, 09:05 AM:

Electrical problems aside, there are 2 other possibilities: 1. Slight mis alignment will yield a "shimmer" when light is very bright 22 ft/lm or more. 2. I assume you have the Christie (no gears/but fears) projector. One of the design errors of that macine is that the shutter is small and close to the film. When very bright the "sharp, optically" edge will be in focus and will be more visible. Louis

Posted by Mark Gulbrandsen (Member # 72) on 03-29-2007, 09:32 AM:

quote: Louis Bornwasser
One of the design errors of that macine is that the shutter is small and close to the film. When very bright the "sharp, optically" edge will be in focus and will be more visible.

Actually you need to check and see if you have double or single blade shutters on your P35GP's. The single blade P-35 does not suffer from the flicker that plagued all double blade P-35's. Any double blade P35GP is convertable to single blade and the conversion takes about 20 min. per machine. Aside fomr elimination of all flicker there is also an increase of about 5% of light output.

Re the DP-70 guy: Check your filter caps in your rectifiers... the ripple may be too high. Not many techs can properly check this. Also, running with a high leg on three phase AC can cause flicker on some rectifiers. Also, make sure your on screen light level is not too high... this is easy to do with a DP-70 although the double speed shutter cuts off very fast allowing higher than nor al light levels. We have run them as high as 22fl with out any visible flicker..

Mark

Posted by Demetris Thoupis (Member # 833) on 03-29-2007, 01:58 PM:

We had an issue with a rectifier and it proved that it had a couple of bad diodes. What I always do is change the whole lot with new ones which are exactly the same. Even though they might have the same specs, an old bunch has some deterioration. What did happen to this house was that when the projector was not running, the lamp performed perfectly. When the projector did run, the lamp had something like a dimming up and down a very low one but really disturbing. It took me a while to figure out that it was NOT the projectors' problem but actually the rectifier. Changed the whole lot of diodes and the problem solved.
Demetris

Sorry for the edit. What you should check, is check the lamp without any film running. That will tell you what is going on.

Posted by Louis Bornwasser (Member # 3063) on 03-29-2007, 03:14 PM:

This problem is more pronounced in 60Hz countries. (12 Hz beat vs 2 Hz beat.) Louis

Posted by Frank Dubrois (Member # 3042) on 03-29-2007, 05:11 PM:

Wasnt lamp focus....I suspect diodes. This isnt the type of problem you can test the diodes for is it? If I'm not mistaken, the diode tests ok until a load is put on it, then I get this flicker Why do some diodes read differently then others? Is a higher number better or worse?

Posted by Mark Gulbrandsen (Member # 72) on 03-29-2007, 06:25 PM:

Remember to ALWAYS replace all the diodes at the same time. I reccomend the Semikron 160 amp diodes in the same size package as the 85 amp jobs that are in there. All you need do is drill the loke a bit larger for the metric thread. Irem uses the Semikrons in all their products.

Mark

Posted by Alex Grueneberg (Member # 2652) on 03-29-2007, 07:23 PM:

Thanks for the input ya'll! I found a brand new diode rack with the plates, slightly higher gage wires with better connection points with slightly larger diodes barried in our supply area. After speaking with my tech I got the ok to swap it out.

#7 now looks beautiful! [Smile]

A shame Dead Silence is playing in it but at least its scope. Now all I need to do is get these couple of spit balls off the screen that I noticed while doing all of this.. [Mad]

Typical.

Posted by Demetris Thoupis (Member # 833) on 03-30-2007, 02:31 AM:

Important tip! The best way to check whether its your projector timing is just throw straight light with no film. If the flicker is visible go straight on the lamphouse/rectifier. If not then there you go on the projector shutter timing.
Demetris

Posted by Eric Robinson (Member # 2966) on 03-30-2007, 10:58 AM:

I was going to suggest rotating the shutter blade out of the light path manually. Shine the light on the screen without the motor running for a brief period of time so that you don't burn the lens. If you see flicker, its from your light source.

Also, since you removed the diode assembly, this would be a perfect time to order new diodes and rebuild it for future use. I keep 2 or 3 spares sitting around for quick swap outs.

Posted by Frank Dubrois (Member # 3042) on 03-30-2007, 11:04 AM:

quote: Demetris Thoupis
If the flicker is visible go straight on the lamphouse/rectifier.

What does that mean?

The flicker is visible without film running.

Posted by Sean McKinnon (Member # 612) on 03-30-2007, 08:33 PM:

I believe that if you had a shorted diode and looked at the light through an open shutter you would not see and "flicker". The "Flicker" comes from the 60 cycle A/C that the shorted diode is allowing across the bulb interacting with the 48 cycle shutter blade. Looking at it through an open shutter would be no different than looking at the light from an incandessant lamp, no visible flicker. You need the 48 cycle shutter to see the effect.

Posted by Frank Dubrois (Member # 3042) on 03-30-2007, 09:30 PM:

So other than swapping out the diodes...I have no clue as to what this could be.

Posted by Alex Grueneberg (Member # 2652) on 03-31-2007, 12:27 AM:

Frank, as I believe we seem to be having similar issues I'd go with diodes for sure. I swapped out another larger flickering house (4k) yesterday night and Meet the Robinsons just for regular old 35 looks pretty darn spiffy. And now I don't get headaches from #4!

Hell, your only in Ohio. Mind if I stop by to catch a flick? [Wink]

Posted by Frank Dubrois (Member # 3042) on 03-31-2007, 01:29 AM:

Sure come on by...replace my diodes and stay for a flick

Posted by Demetris Thoupis (Member # 833) on 03-31-2007, 03:20 AM:

quote:

quote: Demetris Thoupis

If the flicker is visible go straight on the lamphouse/rectifier.
What does that mean?

The flicker is visible without film running.

Start The Projector With NO FILM.
Shine the lamphouse
If flickering then probably is lamphouse

[ 03-31-2007, 12:20 PM: Message edited by: Adam Martin ]

Posted by Frank Dubrois (Member # 3042) on 04-02-2007, 12:08 AM:

When people say they have a spare diode rack sitting around to pop in in case of emergencies, how long does it take you? Where do you disconnect the wires? at the diode? Do you have to then label your wires to reconnect?

curious.....cuz it sounds like a very easy way to replace all 6 diodes..in the light...at my leisure.

Posted by Monte L Fullmer (Member # 2797) on 04-02-2007, 02:24 AM:

If you got a CHR-SLC manual (or have these consoles..), look at pg A-15 in the parts section and you can see the bank that holds these diodes.

They're not too hard to work on (if you know what you're doing), just to ensure that you make sure that you have the correct polarity diodes per each side of the bank and ensure that connections are very tight.

(I still think the bulb is too far into the mirror causing a very slendor cone of light - why of your original complaint on the flicker...)

Posted by Frank Dubrois (Member # 3042) on 04-02-2007, 02:37 AM:

Nope..I checked that. The only thing left is diodes (that I know of). Thats why having a spare rack would be nice. When one goes out, simply replacing the rack instead of on my knees digging around inside the lamphouse and busting knuckles. I like the rack swap idea very much. Any idea on what a bare rack without diodes runs?

Posted by Alex Grueneberg (Member # 2652) on 04-02-2007, 03:22 AM:

I had to replace them individually on one unit. Personally, I disconnected the wires from the junction (where they each meet) and removed the entire heat sink with diodes and all. It's MUCH easier to work on. I'm a much more visual person so maybe I'll snap a pic tomorrow for a better explanation. And as Monte said, the manual does help.

Posted by Frank Dubrois (Member # 3042) on 04-02-2007, 03:10 PM:

I've got a manual, but I was just wondering where you disconnected the rack at...at the diodes or at the other end. A picture would be great. Thanks!

Posted by Phil Ranucci (Member # 3820) on 04-02-2007, 03:26 PM:

Disconnect at the other end, leave the tails on the diodes. This will make it easier to find the bad one(s).Undo the leads to the lamphouse and pull the entire rack out. Then you can work on a bench with plenty of light.Don't forget the heatsink compound.We have spare racks, it makes life much easier. However,if you get one, make sure that it will fit all of your machines, as they differ due to era and capacity.

Posted by Monte L Fullmer (Member # 2797) on 04-02-2007, 10:35 PM:

..and on a small side note while you have your head buried in that console pulling that diode bank out:

On the three-phase, 18 position rotary tap switch, look behind that switch and take a small socket wrench and double chek those nuts that are holding down the wires to that rotor switch plate, for if you have a couple of loose wirenuts there, that rotor switch will go 'kapooie' on you without you knowing about it..(and you wonder why your light output goes real dark all of a sudden..HMMMMM....have you checked this area out some per chance on this flickering issue, per any chance? You could have a winding leg not making the best contact in the world back there....)

good luck, once again - MONTE

Posted by Phil Ranucci (Member # 3820) on 04-02-2007, 11:55 PM:

.and on a small side note while you have your head buried in that console pulling that diode bank out:

On the three-phase, 18 position rotary tap switch, look behind that switch and take a small socket wrench and double chek those nuts that are holding down the wires to that rotor switch plate, for if you have a couple of loose wirenuts there, that rotor switch will go 'kapooie' on you without you knowing about it..(and you wonder why your light output goes real dark all of a sudden..HMMMMM....have you checked this area out some per chance on this flickering issue, per any chance? You could have a winding leg not making the best contact in the world back there....)

good luck, once again - MONTE

OH YEAH, forgot about that. We had that happen on a Sunday evening, the other tech changed diodes but never saw the 1" hole burned through the tap switch. Be aware that the ones you get from Christie now have much larger posts on them, which is good from a reliability standpoint, but bad from a service standpoint since none of the wires will fit and you'll have to put new terminals on all the wiring. We had some old ones that we swapped in. You might get lucky and go to a different tap setting that will give acceptable light until you can get a new switch.

When people say they have a spare diode rack sitting around to pop in in case of emergencies, how long does it take you? Where do you disconnect the wires? at the diode? Do you have to then label your wires to reconnect?

curious.....cuz it sounds like a very easy way to replace all 6 diodes..in the light...at my leisure.

You disconnect the wires where they attach to the terminal board above the diode stack, undo the output leads, unbolt the stack and put the new one in.Takes about 20min. You can label the wires but they really just fall into place and it's easier than it sounds. The stacks are different,or at least ours are, in different models. We have 2K&3K stacks with wire leads off the diodes and a 4K with copper buss bars.

Posted by Frank Dubrois (Member # 3042) on 04-03-2007, 01:02 AM:

quote: Phil Ranucci was the last to post
On the three-phase, 18 position rotary tap switch, look behind that switch and take a small socket wrench and double chek those nuts that are holding down the wires to that rotor switch plate, for if you have a couple of loose wirenuts there, that rotor switch will go 'kapooie' on you without you knowing about it..(and you wonder why your light output goes real dark all of a sudden..HMMMMM....have you checked this area out some per chance on this flickering issue, per any chance?

I had no idea that could even be a problem or how to even locate that. I will look at the SLC manual..I assume that rotor switch plate is listed there?

Posted by Monte L Fullmer (Member # 2797) on 04-03-2007, 02:09 AM:

quote: Phil Ranucci
Be aware that the ones you get from Christie now have much larger posts on them, which is good from a reliability standpoint, but bad from a service standpoint since none of the wires will fit and you'll have to put new terminals on all the wiring. We had some old ones that we swapped in. You might get lucky and go to a different tap setting that will give acceptable light until you can get a new switch.

Yep..been there and done that as well - had a plate burn a good sized hole (got a call from one of my guys saying that one house suddenly went dim and I knew that I changed a bulb recently. Made the dash to the cinema and I went to that switching area and immediately notices position '3' was burnt to no end, but it didn't harm '4' position. Thus, ran the bulb a little on the hot side until the end of the night when I changed a plate out) and had to use the larger style that we had in store..and had to spend two extra hrs changing out the ring tongue connectors to the larger ones on all 18 leads.

Another joy is to drive out that taper pin that holds the selector knob in place on the rotor plate shaft before I could take the defective assembly out.

Also, dbl check all of the 6 leads that goes on both ends of that contactor assembly bolted to the back of that selector baffle plate as well - had to replace a couple of contactors as well due to one leg likes to work loose and smoke up things a bit down there (and if you do smoke one up and have no spare contactor, get a nut type wiresplice and splice the two leg ends together for a good temp fix and wrap with electrical tape until a replacement contactor comes in for replacement).

some fun working with SLC consoles... - Monte

Posted by Frank Dubrois (Member # 3042) on 04-03-2007, 02:16 AM:

Well now were getting involved here. Before jumping into those items, I'm going to switch out the diodes first. I dont remember if I asked, but does anyone know what an empty rack would run? Or do they come packed with diodes? Just a ballpark figure would be cool so I could let them know what to expect.

Thanks again