Film-Tech Forum ARCHIVE: CE LS-40 LED issue

This is topic CE LS-40 LED issue in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Tom Wienholt (Member # 1510) on 06-28-2015, 01:19 PM:

I am having trouble achieving dolby tone. I have boosted the pre-amp gain controls of my CP65 and the gain control on the LS-40 power supply all the way up. Aside from replacing the LED itself, is there any other way of boosting the gain? Thanks!

Posted by Sam D. Chavez (Member # 1841) on 06-28-2015, 05:48 PM:

I believe I answered this question. Look on the PC board of the reader and there should be gain jumpers either soldered in or with links, one for left and another for right. They were mandated by Dolby Labs. If you can't find them call Component Engineering in Seattle. They will know exactly where they are located.

Posted by Steve Guttag (Member # 268) on 06-28-2015, 06:14 PM:

For the 40 system...the locations are there but no wires were ever put in.

Posted by Tony Bandiera Jr (Member # 2365) on 06-28-2015, 09:12 PM:

EDITED to add: Apologies to Sam, I did not see the previous thread where he pointed out the LED bracket alignment...

Tom, the most important first step is to make sure the LED is physically adjusted to the distance from the film AND most critically, the vertical alignment must be spot-on.

Depending on the soundhead involved (Simplex, Century, RCA and Christie all come to mind), you need to loosen the screw(s) supporting the LED bracket slightly, and while running your Dolby tone loop, SLOWLY work the LED bracket up and down (being careful to NOT allow the LED itself to touch the film) till you get maximum output. After you get max output, turn the gain controls in the processor to get Dolby Level.

You will find there is a "sweet spot" (and it's a VERY narrow one) where you will get enough output to overdrive the processor. Even a slight misalignment will drop the gain a lot or give you no output at all. (I got tripped up by this on a service call once...thought I had a dead reader but in reality in the heat of the moment I neglected to check the LED alignment...which was the real problem. I ended up with a brand new at my expense Kelmar reader and LED set for my spares. [Roll Eyes]

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