Film-Tech Forum ARCHIVE: Cp-55 sound issue

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Posted by Tom Wienholt (Member # 1510) on 01-06-2010, 03:36 PM:

Recently I have noticed in one of my auditoriums that the voices were coming of the left screen channel and the center channel. I realize that simply running Dolby tone and balancing the system would solve the problem and it did. However after a few days the same problem occurs and I have to balance again. This is quite unusual and when balancing the Dolby level it is only very slightly off. Is this a problem with the cat150?

Posted by Gordon McLeod (Member # 33) on 01-06-2010, 03:45 PM:

when you say slightly off does that mean the led on the 222 were close
if so i would suspect either the 222 card or the 150 try swapping one at a time
is there an external SR unit

Posted by Tom Wienholt (Member # 1510) on 01-06-2010, 04:19 PM:

Yes the LEDs on the 222 are close. No external sr. Will try swapping cards. Thanks.

Posted by Demetris Thoupis (Member # 833) on 01-06-2010, 05:53 PM:

When doing Dolby Tone use Mono format.
Demetris

Posted by Monte L Fullmer (Member # 2797) on 01-06-2010, 07:42 PM:

Did you run pink noise with a scope attached to the pre-amp card to check X-Y displays to see if the pickup camera is square with the soundtrack on the film?

Sounds like you got a very light case of an out-of-phase issue with azmiuth adjustment - why you got the bleedover in the left channel.

If your optics were dead on square, with those upper four green LED lights on the CAT 242 card, the center channel LED should only be lit when running Dolby Tone. If the left LED is also lit when running Dolby Tone, then you got an azmiuth issue in store with things not being square.

More like an "A-chain" alignment issue more than anything. ..

-Monte

Posted by Gordon McLeod (Member # 33) on 01-06-2010, 10:36 PM:

azimuth errors will steer it to the surrounds not just the left channel
if it can't track the centre or surround it would be left and right lit up not just left as the phase angle changes

Posted by Cameron Glendinning (Member # 3516) on 01-06-2010, 10:57 PM:

Is the sound optics/ solar cell clean?

Posted by Monte L Fullmer (Member # 2797) on 01-07-2010, 01:53 AM:

Could have some elements burnt out in the LED array that could cause some of this issues...

(True Gord - azmuith errors would drift it towards surrounds .. my goof on that call..thx for the correction)

-Monte

Posted by Tom Wienholt (Member # 1510) on 01-07-2010, 01:35 PM:

Ran Dolby tone and the levels needed no adjustment. Replaced the cat150d and the problem was solved. Thanks for the help.