Film-Tech Forum ARCHIVE: Question about PRT-Ultra auto-stop switch

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Posted by Jon P. Inghram (Member # 4125) on 02-06-2009, 05:14 PM:

The auto shut-off switch on our table had been intentionally disabled by placing a piece of film in the bottom of the switch to hold the reset button up so it was always on. Also, the trip wire was bent backwards out of the way. I had to use some silicone penetrating oil to get the external pivot where the wire attaches to move freely, and after removing the film so that the reset switch is free to move it seems to be working just fine.

Does anyone know why someone would have disabled the thing? It's been like that since the theater opened and our tech didn't know about it either.

Posted by Monte L Fullmer (Member # 2797) on 02-06-2009, 07:21 PM:

On a PRT Ultra table that I had in a 4-plex with Mann Theatres, I also had the snag with the trip wire switch as well.

What happens is the weight of the wire itself - especially the weight at the end of that wire - was the cause to trip that switch after awhile.

What I did was find the length where the film would still slap the wire down when the reel was full, to where I could cut off 3 inches of that wire so the wire wasn't that long which reduced the weight at the end of the wire and kept the switch engaged.

Heard some would actually tilt the switch upwards to reduce that weight at the end of the wire where it would shift the weight back intowards the switch, or even bend the wire itelf upwards where it would do the same weight procedure.

I'm quite surprised that they just didn't tie the two power wires together, or put a jumper wire across those wire connections on the switch to bypass the switch completely...guess they're weren't electricians/mechanic at heart..
Something to look at... - Monte

Posted by John Walsh (Member # 168) on 02-06-2009, 07:31 PM:

You will go crazy trying to figure why people do some things in a projection room (and a lot of others places, too!) I'm guessing that pivot was stuck, a previous projectionist couldn't fix it and that's the way it was left until you repaired it.

I never saw one with a weight on the end; only a plastic 'protector' to keep you from getting stabbed. That switch was discontinued, but Lori (hi Lori!) found a box full of them so I think they are still available.

Posted by Monte L Fullmer (Member # 2797) on 02-06-2009, 08:41 PM:

Sorry John - didnt mean to throw a 'curve ball' on the weight subject.. Not an actual added weight per say, but the weight of the object itself.

..I mean to get across on how a long object, when suspended and at a slight downward angle (as the trip wire), that the 'weight' of that entire object will travel downwards due to gravitational pull, and by cutting off some of that wire reduced that 'weight' of the wire to allow the switch not to trip.

Posted by Jon P. Inghram (Member # 4125) on 02-07-2009, 01:38 PM:

I made the wire stick up at an angle so that it sits about an inch away from the edge of a 6k reel. It won't trip by itself, but the weight of some film hanging from it will.

Before fixing the switch I discovered that the gear box had oilers which had never been oiled since at least as long as it's been in our theater. [Eek!]