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Author Topic: Cell wiring Fredrik Sandstrom Film Handler Posts: 63 From: Turku, Varsinais-Suomi, FINLAND Registered: Mar 2014 posted 03-01-2016 07:48 AM                     The 9-pin D connector used on the CP500 and CP45 for optical sound inputs has pins 6 and 9 intended for the "signal ground" connection from reverse scan solar cell circuit boards. Am I correct in my reading of Dolby manuals, that this is the only intended use for these pins, and that they should be unused in forward scan installs using traditional solar cells? I ask because I discovered that in our CP500 install, with FP20 projectors, ACL lasers and normal stereo solar cells, the shield of the signal cable is connected to pin 6. Is this incorrect? Should I disconnect it and solder the shield wire to the metal body of the connector, as per Dolby's instructions? There are no particular problems with this setup, except that the signal is so low that I need to turn the gain up almost to maximum to reach Dolby level. If this is in fact incorrect, what problems should I be witnessing?  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 03-01-2016 09:25 AM                       Using the signal ground pin for front scan solar cells is fine. A lot of the CP500 grounding to the shell and bonding the shell to chassis ground has mostly to do with the arcane difference in codes in UK and USA.  |  IP: Logged Fredrik Sandstrom Film Handler Posts: 63 From: Turku, Varsinais-Suomi, FINLAND Registered: Mar 2014 posted 03-01-2016 10:09 AM                     Thanks, Sam. It is confusing because Dolby only mentions these pins when talking about connecting reverse scan readers, and in field bulletin 206 we can read: "This connection must not use the shield of the optical input cable, otherwise RF energy can be imposed on the Cinema Processor ground system." and further "The wire [...] should pass inside the same shield as the optical input cables and not connect with the shield at any point." But in this setup, you're saying it's perfectly fine to have this connected to the shield? By contrast, in my home setup, where I have Cinemeccanica's reverse scan reader, I have followed Dolby's instructions, despite the fact that the cable I originally got with the reader was actually wired contrary to these instructions.  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 03-01-2016 10:11 AM                     Regarding the low signal level: Perhaps the LED's in your sound reader have aged to the point where they are no longer able to put out enough light to give a decent signal level. LED's DO age and degrade with age. I've had exactly the same very poor signal level problem you've described several times, and in both cases, replacing the LED light source brought the signal level back up, and them some.... Another thought- Also, you just may want to check the actual cell-to-processor wiring, to make sure you don't have a slight unintentional ground or short somewhere that's pulling your signal level down.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 03-01-2016 01:25 PM                       quote: Fredrik Sandstrom By contrast, in my home setup, where I have Cinemeccanica's reverse scan reader, I have followed Dolby's instructions, despite the fact that the cable I originally got with the reader was actually wired contrary to these instructions. As I implied/inferred, there's some butt covering as regulations vary. Using signal ground is essential for reverse scan but optional for front scan.  |  IP: Logged Fredrik Sandstrom Film Handler Posts: 63 From: Turku, Varsinais-Suomi, FINLAND Registered: Mar 2014 posted 03-01-2016 04:14 PM                     quote: Jim Cassedy Perhaps the LED's in your sound reader have aged to the point where they are no longer able to put out enough light to give a decent signal level. LED's DO age and degrade with age. These are lasers, which I understand should have very long lifetimes compared to LEDs. And it's been like this for as long as I have been involved in this venue, four years now.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 03-01-2016 06:36 PM                       The lasers may need to be mechanically aligned so they peak right into the center of the lens. Basically it's just figuring out how to rotate the bracket holding the laser diode while running test film and observe when you see the peak in audio level. Easier said than done with a laser but it's possible. Maybe the readers were never set up properly as it's difficult. Laser diodes wear out just like all other LEDs. Usually though, they just stop working one day and show is over.  |  IP: Logged

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