Film-Tech Forum ARCHIVE: Peculiar Dolby Digital problem

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Posted by Peter Castle (Member # 1997) on 10-10-2004, 04:43 AM:

We have a Kinoton FP25E with a basement Dolby Digital reader.
A few months ago, we encountered a problem where our CP500 would
report a jumping error rate, skipping from say 4 to F back and forth. Having read through the items on this forum, I noticed an item about O-rings and called our service people. Without prompting they suggested it might be the o-rings, so they were replaced several weeks ago. Our Dolby Digital has been very very stable since - it will even sit at 7 on some older prints without ever going to F.

Unfortunately a very strange thing happened on our last screening. We were running a very good print of "Fahrenheit 9/11" with the CP500 reporting a stable 4. However we were actually using the SDDS track (I prefer it - don't open another discussion as to why). In the last reel I noted that the SDDS reader was intermittently dropping a side of the film, so I decided to put the SDDS unit into bypass, as the Dolby was so stable. Immediately, the CP500 went into the oscillating mode again! So back to the (only slightly) unstable SDDS.

Before our next screening (of the director's cut of Donnie Darko), I power cycled the CP500. However the Dolby continued to oscillate until the last reel of Donnie Darko when it stabilised again.

Any ideas?

Posted by Leo Enticknap (Member # 534) on 10-10-2004, 05:04 AM:

Fluctuating power supply to the LED?

Posted by Stephen Jones (Member # 16) on 10-10-2004, 09:02 PM:

Hi Peter,
Have had the same problem off and on with our FP50D's.You could try replacing the o rings with the newer green ones which are made from a different compound than the black ones.Or another problem is the pressure on the layon roller this is what our prob was with the same symptoms you are discribing.But be warned when adjusting the pressure it is very critical.I had a tech show me how to do it might be best if you get someone out to show you how to set it as to much will force out the film out not enough and you have the prob you have been discribing.

Steve

Posted by Chris Byrne (Member # 1563) on 10-11-2004, 06:02 AM:

O-Rings only need to be replaced if they are cracking or have uneven wear.

To avoid getting a twist when applying a new set, start them at opposites ends of the lay-on roller and roll towards the furthest slot.

Shoddy bearings in either the lay-on or stabilizer will also give intermittent error rates.

Posted by Steve Guttag (Member # 268) on 10-11-2004, 08:06 AM:

Chris,

Not necessarily. Kinoton had a bad batch of the black O-rings. They would pucker up and no longer fit (ID, OD or even diameter). The Green ones Kinoton currently is supplying is not suffering from this problem so only those are known to be safe of a new batch.

It doesn't take too long for a bad O-ring to show itself so if you have a set on that has been there for a few months...they are probably going to be just fine for quite some time.

Steve