Film-Tech Forum ARCHIVE: Testing Cat 701's without test film

This is topic Testing Cat 701's without test film in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jeremy Weigel (Member # 4208) on 12-29-2013, 10:05 AM:

I have a few Dolby 701's and DA20's that have been out of service for a couple years and have a few potential buyers. Is there a way to test the strength of the LEDs without running 69T film?

Posted by Steve Guttag (Member # 268) on 12-29-2013, 12:45 PM:

The strength? Yeah, pretty easy with an O-Scope...run any DD film (Trailers...etc) and look at the whiter-than-white burst (when it is reading the perfs)...it should be 4.0 Vp-p, ideally...By 2V p-p things get dicey.

I wouldn't base any alignment on non-measured film but just LED level...nothing fancy is required.

Now, if you have a CP650 laying about...use it. Either on the CP650 software or via the front panel (need to put it in tech mode)...the CP650 will read out the output level in volts with 1/10V accuracy.

Posted by Sam D. Chavez (Member # 1841) on 12-29-2013, 12:52 PM:

I think maybe Jeremy doesn't have a convenient way to roll film.

Posted by Jeremy Weigel (Member # 4208) on 12-29-2013, 03:40 PM:

Thanks Sam. Guess I should have been clear.

Posted by Louis Bornwasser (Member # 3063) on 12-29-2013, 05:46 PM:

You could just turn it on and check video level. The perf is a hole so even with no film that part would read correctly.

With basement readers, we could set up with no film and get good usable results. Then, with film, we then tweaked it to spec. 90% of the way there with no film or motor. Louis