Kind of long winded but any help would be appreciated.

Tag along question: Its probably here somewhere but what is the absolute best thing to clean the platter discs with to keep down on slickness?

Remove the center brain roller on the platter and look inside it. Remove that spring and then re-install the roller. Your bounce should be gone at that point.

If you are having a tension problem, the reader's green LED light will blink a lot. You need to find out where the tension problem is first. See if it is in front of the reader or after the reader. To do that, run the film and gently press the film with a finger. When the reader's green light comes on solid, that tells you where the tension problem is.

If it is in front of the reader, is usually fixed by swinging (the reader's) auxiliary roller as close as possible to the large center roller. This produces the maximum amount of film wrap and adds tension. Sometimes adding a roller or a cleaning roller helps as well.

If the film is bouncing from the platter, then the fix your tech came up with might work. Be aware, however, that it could cause the problem to worsen. That spring in the center roller (on a Christie platter) is there to add tension. Of course, the spring must be in good working condition.

If the bounce is after the reader, check the projector's film guides, sprockets, and motor belt.

Lastly, it could be a reader that is out of calibration. Try swapping with a known good reader to see if the problem goes away. If it does, then contact us for a repair/exchange.

Good luck and see what works best in your installation. Please contact me if you have any questions.

The way your post is worded is confusing the need to add tension with the need to keep tension even. Removing the center spring from a Christie brain will stop the bouncing, unless one of the rollers is damaged (usually the older black ones are suspect). The dts reader runs very happily with a lot of tension or virtually no tension. It's just those situations where there is a bounce where a problem occurs. Go to a theater with a platter that has virtually zero backtension and watch as the dts reader plays without a hitch and I think you will see what I am trying to clarify.

Now you need to put the spings back in to tension up your SDDS reader

Actually, the springs in the center rollers can be a help or a hendrence. If properly set and maintained, they will offer a smooth, higher tension payout. This can be useful if the platter is separated from the projector a bit and you don't want to add extra rollers to the path. But the key is that the lubrication on the spring has to be kept fresh and the spring should be formed to put just the right amount of tension on. I have never had a problem with them.

I would definately check the other rollers in the film path. I am finding, in a lot of places, that both green and black rollers are now wobbling and essentially turning eccentricly. This will wreck havoc on any digital reader. If you see that the film is jerking as it goes from the platter to the projector then somthing is amiss with your rollers. One of my customers has changed or is changing most or all of his rollers to ones with needle bearings inside (the metal ones for the flangless rollers) like are used on the MUT.

Steve

I don't think it is necessary to re-design the whole shebang when just an additional roller did the trick.

First, I tried more rollers above DTS reader before I wrote the post and it only served to reduce the times the reader fell out of sync. Hence the problem not solved.

I am posting late/early because of multiple build ups and techs for sneaks.
I'm going to go ahead and replace the shafts when thay arrive, but I am gonna give removing the spring a try. It just kills me to have only one out of nine theatres in dolby and it be a print of Harry. Manager doesn't listen when I inform him of these things.

Am sure this will take care of problem and if it doesn't I'll switch out readers and see what happens.

The deal with tension is that (and you are correct) that tension needs to be constant. Most times I have found adding tension is the key. Very seldom have I seen tension needing to be eased. That is why I wrote that you need to find out what works best for your installtion. No two installations are the same and each may need different adjustments.

The finger trick always works to find out where the problem lies. Then, you just have to zero in on the location and make the necessary adjustments (earth ground the projector chassis, add/ease tension, replace a bad sprocket or motor belt, etc).

If anyone needs help resolving timecode reading problems, please send me an email and we'll go over it in detail.

Karen at DTS
khultgren@dtsonline.com

I can't tell you how many times in the past week I have seen Christie rollers (Green or Black) turning out of true and that INCLUDES brand new ones...sure the look fine but when running, the three centerfeed rollers will start to beat off on another and you can see the bobble come and go from very erratic to very smooth. The large diameter of the rollers causes the frequency to be so small it can oscillate since the rollers are semi-massive (with two different masses) the system acts under-damped. The springs in the rollers not only add tension but offer damping via the viscous grease inside the roller. It is kinda like the dash pot inside a penthouse reader...the job being to merely kill any oscillation. Once critically damped, no further tension or damping is needed. The system is certainly crude, in this case but it can be quite effective. IF Christie had perfectly machined rollers with pefectly centered holes, then there shouldn't be any bobbling but my findings are that they don't meet that criteria. Futhermore, the roller's holes open up with time and allow it to move even more. Another trick that might work would be to make the flangeless rollers have an OD smaller than the diameter of the film contact area of the flanged roller...that is, have the flangeless rollers runn at a different (faster) speed. This would have a natural tension that would put some drag on the middle roller.

Steve