Film-Tech Forum ARCHIVE: Strange Red Reader problem

This is topic Strange Red Reader problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Matthew Taylor (Member # 2310) on 11-14-2006, 10:31 AM:

A friend of mine does special mobile screenings for events. He recently converted his Philips FP23 to a philips red (laser) reader (not reverse scan). The event was setup and the A and B chains done by a dolby technician and then they ran a test screening of the whole feature film which was all fine.

With the conference hall full with the audience, the film was started but the red reader was 'pulsing' causing the sound to 'pulse' too. The power supply to the laser was swapped out but the problem persisted. The show was cancelled. The strange thing is, the moment everyone was gone, my friend tested the rig again for over and hour and the laser was rock steady.

What could be the cause (and solution)?

Posted by Monte L Fullmer (Member # 2797) on 11-14-2006, 01:03 PM:

"pulsing" - was this a 50Hz pulse ..or some other frequency pulse..like sprockethole "motorboat" pulse?

Just need the specifies on what kind of pulse occured..to help you out...

Posted by Louis Bornwasser (Member # 3063) on 11-15-2006, 05:11 AM:

Must suffer from BLS: bashful laser syndrome. Louis

Posted by Matthew Taylor (Member # 2310) on 11-15-2006, 10:08 AM:

Well, I just spoke to my friend and asked him to describe more fully the type of pulsing. Perhaps pulsing is the wrong word because apparently it's a regular but intermittent (ie with no pattern) kind of interference where the sound will drop out either partially or completely, a bit like there's a loose connection. Within a space of a minute or so, it would happen lots of times and yet before and after the screening it ran with no problems whatsoever.

Posted by Richard Fowler (Member # 893) on 11-15-2006, 11:27 AM:

Some lasers are sensitive to RF from xenon lamp ignitors and emissions from motor invertors. Proper power supplies, shielding and possible use of ferrite beads are items to consider.

Posted by Matthew Taylor (Member # 2310) on 11-15-2006, 11:46 AM:

Would it be possible that the laser could be affected by the RF emissions from mobile phones or bluetooth devices? That would explain why it was fine when there was no audience.

Posted by Demetris Thoupis (Member # 833) on 11-15-2006, 03:22 PM:

Had an approximate same issue with a V4 projector where the exciter / later reader switch was not making a clean contact and the volume was increasing and decreasing irregularly. Is the laser's power supply connected directly on the unit or is there a switch in between. If so try and connect the power supply directly and see if there is no problem. Was there any A/C units on when they tried it? Did they switch the A/C's on when the people where in? What is changing between the time he does the test and the time the people are in the theater. Some queries to help you sort it out.
Best Regards

Demetris

Posted by Peter Hall (Member # 695) on 11-18-2006, 05:01 AM:

HI

It is worth checking the power supply to the laser - sounds like the mains may be dropping (as I believe there was a pile of adjacent kit powered up only due the actual performance). Voltage to the laser itself should be 3.7v, or before the diodes 5v. The laser is OK for + or - 10%.

Where is the mains for the laser PSU derived from ? Might also hbe worth checking that the laser is isolated from the projector chassis, lest the xenon strike upsets it