Film-Tech Forum ARCHIVE: Airpot in Cat 702 reader not replacable?

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Posted by Joe Redifer (Member # 3) on 10-10-2010, 10:41 AM:

We don't have the parts manual for the Dolby Cat 702 reader here but we do have one for the 701. I need the airpot (or dash pot as Dolby refers to it). The 701 manual gives a number for the cylinder but says it is not user replaceable. WTF?

Anyway, I need an air pot. There is too much vibration without it. Replace/repair the ENTIRE reader?

Posted by Louis Bornwasser (Member # 3063) on 10-10-2010, 12:03 PM:

Almost all the parts are the same; 700,701, 702..

The airpot is available. I stock them. I will look up the number tomorrow.

You will find that the threads are not quite a match and are quite fragile. Louis

Posted by Steve Guttag (Member # 268) on 10-10-2010, 02:43 PM:

Adjusting the airpot can be tricky. You really just want the minimal amount of damping that allows it to dampen. People over-damp way more than under damp. Remember, most of the damping occurs with the flywheel. The airpot augments that by minimizing outside influences, like out-of-round transport rollers or uneven clutches.

90% of the time, the airpot fails due to the shaft that connects to the plunger becomes disengaged. An appropriate spot of epoxy where the shaft connects to the plunger will normally permanently fix it.

Posted by Joe Redifer (Member # 3) on 10-10-2010, 02:55 PM:

I would, but the airpot appears to be completely missing. Only the cylinder is present.

Posted by Christos Mitsakis (Member # 143) on 10-11-2010, 02:49 AM:

Joe,
You're missing the whole piston, or plunger as Steve calls it.
There is a replacement kit (part 83159) that includes everything that is needed. I don't know if the piston is included in the airpot, (ie cylinder part 65163) or attached to the airpot arm (part 67176)if you want them separately.

Setting correctly the damping amount (per Dolby instructions) is a pain, as Steve described. Too little space to adjust the airpot screw with ease, plus you have to be extra careful.

C,

Posted by Joe Redifer (Member # 3) on 10-11-2010, 03:43 AM:

Thanks for that, Christos. I will be prepared for a frustrating ordeal.

Posted by Joshua Waaland (Member # 287) on 10-11-2010, 02:39 PM:

The airpot in my 702 is broken also and I have been putting off getting it fixed. Nice to have this info though when I do get around to it.

Posted by Louis Bornwasser (Member # 3063) on 10-11-2010, 02:54 PM:

The complete dashpot assembly is # 6502500.

Adjustment is critical but easily done. You want a faster response, not a slow one. Looking at the scope, you are adjusting the dashpot for minimum "flagging." If in doubt, look at a correctly functioning reader and mimic the "recovery" time.

btw: the main reason these fail is "overrotation" or something stops the film and the film snaps the 2 arms open. It is possible to adjust the arm-angle so that the arm hits a stop before it breaks the dashpot. None from the factory are correct. Louis

Posted by Richard Hamilton (Member # 321) on 10-11-2010, 03:38 PM:

Joe,
I sent you a PDF file from Dolby with step by step instructions on replacing the airpot. I sent the PDF to Brad as well to post here on this thread, but haven't got it back yet.
Rick

Posted by Joe Redifer (Member # 3) on 10-11-2010, 04:10 PM:

Thanks Rick, I got it. Brad also forwarded me your e-mail so now I have two to choose from. [Smile]

And yes, I have another 702 with the airpot intact so I will mimic that one.