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Posted by Richard May (Member # 2627) on 06-28-2005, 08:17 PM:
 
We may have gone through this before, but does the LED go dim over time to the point where it needs to be changed. I have one at one theater that has been in use for six years. It is always kept on. Now all the movies that run, even the new prints, will not hold better than 7 or 8 on the error readout. Also bounces back to F to the point where it will not play digital. It does the same thing with brand new test film. I did not have the scope with me at the time to check it out.
 

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Posted by Louis Bornwasser (Member # 3063) on 06-28-2005, 08:28 PM:
 
1. Yes, the LED slowly fades out.
2. Dirt, smudges on lens and LED may be a factor.
3. Anything mechanical that causes wow/flutter, bad sprocket will cause faults.

LED most likely due to time involved. (If possible, power the 701 off of the motor circuit so it does not run except during the actual show.)
Louis
 

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Posted by Richard May (Member # 2627) on 06-28-2005, 09:07 PM:
 
Thanks Louis,
I did clean the lens and led. I ran new film to test with. Everything ran smoothly.
 

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Posted by Mark Gulbrandsen (Member # 72) on 06-29-2005, 07:40 PM:
 
Richard,

The LED current can be adjusted inside of the 701 to compensate for LED fade. If this has been running a long time then having it tweeked for correct video level is a good idea. I can guarantee you that video level will be low! Cleaning the lens and optics may get you by and gain you just enough extra video level to be able to decode, but not for long. I had a customer that had turned his voltage level up too high for what ever dum reason and this also caused the input opf the Video card to bury the datalevel into the pedestal causing a constant F reading. The adjustment is simple but a scope is necessary for this!!

Mark
 

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Posted by Richard May (Member # 2627) on 06-29-2005, 09:11 PM:
 
Thanks Mark. I thought there might be voltage adjustment. I'll bring the scope and try it.
 

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Posted by Ken Jacquart (Member # 369) on 06-30-2005, 11:56 AM:
 
Additionally, if you ever replace the LED, remember to turn the current back down in order to preserve it's life expectancy. Incidentally, you can RXO the LED / heat sink assembly. It is Dolby part number 83308. If it has been in service for six years, you are fortunate that it's still produce enough video amplitude.
 

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Posted by Richard May (Member # 2627) on 07-11-2005, 07:00 AM:
 
Just a quick note. I raised the LED output level slightly and the error rate dropped from 7 to 3. It plays perfectly now. I will just have to lower the LED level whenever I change the LED. Thanks again everyone.
 

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Posted by Brad Miller (Member # 2) on 07-11-2005, 02:43 PM:
 
Just an FYI in the simplest terminology that I can explain here...

Although you probably greatly improved the calibration of that reader by upping the led output to the point where a "7" print is now tracking at a "3", you could've also been running a bit of a "dark" SRD track at the time and as such "lighter" tracks will now F due to having too much light shining through the track. Make sense?

Of course if it's been running for 6 years, maxing it out is honestly probably what needs to happen to achieve level as close as possible to ideal.
 

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Posted by Richard May (Member # 2627) on 07-11-2005, 03:16 PM:
 
It does make sense, Brad. This has been happening over the last few months with many prints. They just don't tell me things that are going wrong until much later than they should. I did not have to max out the adjustment, either. Just a little bit of gain did the trick.
 

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Posted by David Graham Rose (Member # 1450) on 07-12-2005, 03:14 PM:
 
Greetings to you all

Louis is indeed correct. Hello Louis - good to hear from you and hope you are well. We met many years ago at ShoWest! Hope you still have your aeroplane for emergency call outs!!

All the projectors that I have ever researched here in Cambridge have been modified to switch on the LED array with the commencement of the motor. I have calculated that one will obtain many additional months life from an LED switched in this manner, unless of course the theatre is running continuos performances, as occurred here in the UK in the '40's and 50's.

From Cambridge,

Goodnight
 

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Posted by Mark Gulbrandsen (Member # 72) on 07-12-2005, 05:43 PM:
 

quote: Brad Miller

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Although you probably greatly improved the calibration of that reader by upping the led output to the point where a "7" print is now tracking at a "3", you could've also been running a bit of a "dark" SRD track at the time and as such "lighter" tracks will now F due to having too much light shining through the track. Make sense?

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