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Author Topic: Reverse Scan Reader Gain Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 11-17-2009 03:55 PM                     Do all reverse scan readers have an adjustable high/low gain setting?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-17-2009 04:22 PM                     Most have a jumper you cut to increase the gain of each channel  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 11-17-2009 04:40 PM                     and the reason for wanting this?  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 11-17-2009 05:11 PM                     We are going through LED's too quickly at one place.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 11-17-2009 05:57 PM                     It would help to write the model of the reader and projector head or soundhead. Also a brief description of the set-up. Average life-span of LED is good well 5 years.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 11-17-2009 07:30 PM                     You may also have a bad reader board or solar cell....a lens problem...or power issues to the LED.  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 11-17-2009 07:36 PM                     My experience is they last less; about 3 years. If the LED power supplies could be wired to the motor power, they might (depending on usage) last longer since they would not be on all the time. If the heat sink compound is not applied when replacing an LED, it might overheat, reducing it's life.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-17-2009 09:48 PM                     I typically get 5 to 7 years out of LEDs and here's why... What Dolby reccomended a number of years ago to prolong LED life is to turn the preamp gain almost all the way up and set the LED current(or voltage depending on make of supply) down to get to Dolby Level then slightly balance out one or both channels as needed to get exact Dolby level. I've done this for years with systems that don't have excess noise in the preamp and it greatly prolongs LED life span. Also make sure that your power supply has been modified if needed. Some older Component Engineering and Kelmar units that were made for IR leds can not be turned down low enough and you'll have extremely short LED life span as a result. I reccomend checking the current through the LED to make sure it's at a reasonable level and the power supply is functioning properly. Also consider switching on and off all reverse scam power supplies in any complex. Since there is typically a delay before going to analog this is generally not a problem. You can sometimes use the generally unused exciter contacts in the automation to do this. The power supply can also be wired across the motor circuit. What ever is easier and meets local codes. Hope some of this helps.... Mark  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-17-2009 10:14 PM                     Sadly, BACP units don't have this availability with adjustable LED current (there must be a reason why of this against other units that do have this..). I just did a BACP LED replacement and reconnected the gain jumpers on the preamp card so I can have more headroom with the preamps levels since they were wide open and I couldn't get Dolby level prior to the install .. and I was getting some decent noise from the wide open preamp card on the CP55 unit. But the original LED has to be a good 6 yrs old before starting to fade..which I think is a good enough life span. Now, just need to figure out to be able to switch off the LED while machine is at rest and comes on when power to motor is enacted. This will buy tonnage on LED duration. -Monte  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 11-18-2009 12:04 AM                       One reason BACP did not make the LED current adjustable is due the tendency of many techs to reach for the adjustment pot instead of looking at mechanical alignment to make sure you have max light before looking elsewhere. So say you have an LED way out of alignment. You run the current all the way up to make Dolby level and exacerbate the LED wear issue by running the LED at 300 mA instead of the 150 mA we decided was the best compromise. Mind you, we made sure there was 8 dB over Dolby level on a properly aligned reader with a new LED. This was intended to make the LED last 5 years more or less after cutting the gain jumpers at about 3 years. It has proven to be about right after 11 years out there in the field.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-18-2009 12:48 AM                     quote: Sam D. Chavez looking at mechanical alignment to make sure you have max light before looking elsewhere. .. like loose holding screws, azimuth adjustments, oil-filled lens tubes, et.al. quote: Sam D. Chavez we made sure there was 8 dB over Dolby level on a properly aligned reader with a new LED Fully agree here. After what I did with the reinstall and got everything back to square with the 'o-scope', I had to really turn down the trimpots on the preamp card just to get the proper dolby tone levels. thx-Monte  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 11-18-2009 01:26 AM                     I've never had any problems with the gain on the BACP. And been running for years now with no problems. Demetris  |  IP: Logged

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