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Topic: Christie P35C sound warble

Jim Bedford
Jedi Master Film Handler

Posts: 597
From: Telluride, CO, USA (733 mi. WNW of Rockwall, TX but it seems much, much longer)
Registered: Jun 99

posted 01-18-2000 11:01 AM

I have two Christie P35C projectors in my booth. One works just fine, but the other has developed an intermittent sound warble. You can’t hear the problem during dialog, but when there is symphonic music, it is often very apparent. It's just a second or so of warble out of a minute or two. It happens at various times in the takeup, without being consistent. It might happen 3 or maybe 18 times in a reel on just the one projector.

I’ve had a few suggestions on how to cure the ill, but nothing has worked so far. I’m here for more ideas.

I have taken apart the takeup assembly and completely cleaned and reinstalled it and run it at different tensions. Nada improvement.

I have tried threading at different tensions around the sound head and that makes no difference.

Ideas?

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 01-18-2000 12:18 PM

Try this. Thread the soundhead with absolutely no tension. In fact, make sure there is 1 sprocket hole past zero tension. Now watch the "bulge" of film between the lower constant feed sprocket and the sound drum. Does it bounce loose and tight and loose and tight? If so, change the sound drum bearings. Make sure to order them direct from Christie and not to use any "generics", as I've tried the generics and they did not last 3 months in a regular booth environment.

I'm not sure if this will help your very intermittent problem, but you should check it out anyway. What makes you think the takeup is causing the problem? Also, what were the other suggestions given to you previously?

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Ian Price
Phenomenal Film Handler

Posts: 1714
From: Denver, CO
Registered: Jun 99

posted 01-18-2000 01:23 PM

Hey Brad, Joe.

What about the air-pot damper?

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 01-18-2000 03:46 PM

I completely forgot about that Ian. Odds are he's already check it, but if that little rod is bent or broken, it must be replaced.

The trick I've found is to snip the end of the rod off with a pair of wire cutters just a touch. This way, even when the lower guide roller is completely down, the air pot won't "quite" hit the bottom and will never break again. Apparently Christie's already though of this though, as the last replacement assembly I got had a stopper bracket for the arm.

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Jim Bedford
Jedi Master Film Handler

Posts: 597
From: Telluride, CO, USA (733 mi. WNW of Rockwall, TX but it seems much, much longer)
Registered: Jun 99

posted 01-19-2000 06:04 PM

I think Ian has identified the problem. The air-pot on my #2 projector does not behave like the one on #1. On #1 it is clearly damped and moves slowly when depressed; the one on #2 shows no such dampening. Nothing is obviously broken, but I suspect it is bad. Anyone know where can I get a replacement or even a used one?

Brad, there's a guy on HIAC 35mm forum looking for a manual on the P35C. You have a P35 listed in your Adobe Downloads. Is that almost the same head? He's looking for a parts list.

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Ian Price
Phenomenal Film Handler

Posts: 1714
From: Denver, CO
Registered: Jun 99

posted 01-21-2000 01:40 AM

Joe,

Do you have any air-pots that you may spare? Do you have any that may not live up to your 72 shows a day, standard? Perhaps you could send one jim's way?

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Stephen Jones 1
Film Handler

Posts: 62
From: Tulsa, OK, USA
Registered: Aug 1999

posted 01-22-2000 06:01 AM

The sound warble, unfortunately, is an all to familiar problem with me. Here is what I have found causes it:
The airpot breaks or isn't set correctly. There's a screw on the bottom on the airpot that controls how fast or slow the airpot bobs. If you don't have a replacement, you need to talk out the rod so the tension arm can move freely and thread as you normally would. On some, I've found that no tension eliminates much of the warble.
The other cause I've found is when the bottom loop is too small. Right before the next intermittent cycle, it tugs against the pad roller and cause a very bad vibration on the top tension arm. It will warble very badly in this case.
The bearings in the sound drum could also be going bad. Try spinning the drum and see how easily it spins. The warble is caused because the speed of the drum isn't matching the speed at which the film travels.
And last but not least, the way the soundhead is threaded. One sprocket tighter than loose is perfect.
You can order the airpot assembly from Christie for about 32.50, I think. I always have alot on hand.

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Jim Bedford
Jedi Master Film Handler

Posts: 597
From: Telluride, CO, USA (733 mi. WNW of Rockwall, TX but it seems much, much longer)
Registered: Jun 99

posted 01-22-2000 12:53 PM

Thanks for all the input.

It's not the loops as I thread both projectors identically and the warble only happens on #2.

It's likely not the sound drum bearings as both drums seem to move similarly.

The airpots do not behave the same and the one on #2 does not appear to be dampted as it moves with very little resistance.

I plan to take it apart and clean it and reinstall it. As in most of the mechanical world, this seems to solve 96.3% of the problem.

Does anyone out there have an airpot for a Christie P35 series for sale. Please post me directly if so.

And those of you on the left coast, thanks for sending us the 9" of snow overnight. See you later, I'm going skiing.....

More later.

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Jim Bedford
Jedi Master Film Handler

Posts: 597
From: Telluride, CO, USA (733 mi. WNW of Rockwall, TX but it seems much, much longer)
Registered: Jun 99

posted 02-12-2000 10:34 AM

Airpot update:

My P35C's have no airpots. They are oil dampted pots. Just little graphite 1 1/2 inch high cups filled with damping oil with a graphite piston attached to the lower sound drum roller that fits into the cup. Both are filled to the same level. One damps just fine and the other don't damp.

Why? Is the graphite worn on the piston or along the side of the cup not allowing for hydraulic damping? Any other ideas?

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 02-13-2000 02:00 AM

Where's Bevan?

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