Film-Tech Forum ARCHIVE: Calibrate analog LED

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Posted by Antonio Marcheselli (Member # 373) on 08-16-2002, 04:14 PM:

Hi everyone.

I've just read the Dolby procedure about calibrating the analog's LED.

It speak about "gain adjustment on the cinema processor optical preamp board".

On CP500 is this gain control the gain I can found on the "dolby level" page? Or is there another gain control on CP?

Thanks!

Bye

------------------
Antonio Marcheselli
Florence, Italy

Posted by Manny Knowles (Member # 1171) on 08-16-2002, 05:17 PM:

Antonio:

I'm just trying to clarify what it is you want to do...are you interested in setting Dolby Tone level using Cat. 69T film?

~Manny (The best tobacco money can buy!)

Posted by Gordon McLeod (Member # 33) on 08-16-2002, 06:04 PM:

Antonio the gain adjustment on the optical preamp is set in the Achain alignment menu as dolby level

Posted by Jean-Michel Grin (Member # 1360) on 08-16-2002, 06:10 PM:

Antonio,

The only gain on the CP 500 is the one that control the dolby level.
Raise this level to the max, and reduce de current inside the red LED. (a trimpot is located in is power supply) to obtain just a little more bit than the dolby Level (Of course you must have a loop of CAT 69t running in the projector)
At final reduce the dolby level of the cp 500 to obtain the right level.
Please pay attention tha your reader must be alignated perfectly and clean !
For more information, consult the service bulletin No SB-0011 and SB-0012 at www.strong-cinema.com
Component Engineering website can be helpfull too

Good Luck, and I beg your pardon for my weak english !

------------------
Jean-Michel Grin - Europlex Cinemas (Switzerland)

Posted by Brad Miller (Member # 2) on 08-16-2002, 06:31 PM:

I'm going to chime in with one very important and often overlooked tip. Check the alignment of the led bracket!

On pretty much all of the led/reverse scanning systems I have used there is a small amount of play in the mounting of the led bracket. That play will make a world of difference in the life of your leds. As an example, I have converted a lot of soundheads with the Kelmar kit. Once I have a rough alignment I run a cat69T loop and slightly loosen the screws just enough to move it around. Listening through the port window or monitor will show just how much of a difference this can make. I have one complex with 3+ year old Kelmar red led upgrade kits installed in them and the power supplies for the leds are STILL all set at minimum output, and reaching Dolby tone is effortless with extra headroom. When that range finally starts to die then, and only then will I start increasing the power to the led.

Posted by Antonio Marcheselli (Member # 373) on 08-16-2002, 07:08 PM:

Manny,

No, I would like to set the LED's power!

I didn't know that there was an "official" way to set the power level of that LED.

I don't have instruments to perform an A-chain adjustment (and I'm not able do do it!) our projector just need a check of the level.

Jean-Michel,

Thanks for the links and no problem with your english, what should I say of mine...

Bye
Antonio

Posted by Michael Schaffer (Member # 1204) on 08-16-2002, 07:37 PM:

Also read the Dolby field bulletin No.218 available here. Which projector do you have?
Michael

Posted by Antonio Marcheselli (Member # 373) on 08-17-2002, 04:39 AM:

Michael,

I've that Dolby bulletin. Unfortunately my analog reader doesn not have the gain jumper, only my digital one have it.
Analog one is cinemeccanica labeled...

Projector is Victoria 5 consolle.

Bye
Antonio

Posted by Antonio Marcheselli (Member # 373) on 08-17-2002, 11:36 AM:

Today morning I've cheked the LED power. Following the Dolby procedure I've drop the LED current of approx 250mV.

Now the Dolby analog Gain is almost at maximum. Is it as it should be?
I thought that Dolby gain should stayed at 50%.

Bye
Antonio