Film-Tech Forum ARCHIVE: Potts Platter Takeup/Payout Problem

This is topic Potts Platter Takeup/Payout Problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Patrick Matthews (Member # 2705) on 12-29-2009, 11:27 AM:

My Potts Platter is quickly becoming unreliable. I have narrowed it down to the variac. It seems that it will no longer engage the motors when the take up plate is pinned. This is usually the area that the take up plate hovers at during normal operation. Now it seems like that area is about 1/2"-1" below where it should be causing the motors to not engage when they should and then spin too fast when they do.

So, is this the brush going bad on the variac motor or do I need to reset electric zero with the variac hub?

Posted by Kirk Futrell (Member # 5006) on 12-29-2009, 12:00 PM:

Make sure the button switch on the variac isn't gummed up. Remove power to the variac and spray the switch with contact cleaner and push the button several times. You may even want to lightly lube the switch so it travels in and out smoothly. Also make sure that all the bolts and screws holding the variac arm together are lubricated and properly tightened, so the angled plate that hits the button switch on the variac does so at the correct time. This worked for me when I had a similar problem, of course the problem you are experiencing may be less superficial, in which case I can't help.

Posted by Monte L Fullmer (Member # 2797) on 12-29-2009, 12:32 PM:

quote: Patrick Matthews
So, is this the brush going bad on the variac motor or do I need to reset electric zero with the variac hub?

I've seen brushes go bad - both the button and the brush itself..have you tried to reset to electical zero yet?

Posted by Paul J. Neuhaus (Member # 3205) on 12-30-2009, 03:39 PM:

Probably the zero. But, I agree with the above about a good cleaning. Things can get jarred out of place in time. Think about it everytime a show ends the variac arm slams to the bottom. You're headed in the right direction.

Posted by Mark Gulbrandsen (Member # 72) on 12-30-2009, 04:17 PM:

YEp! Check the rotor brush... not the ccarbon one but the one near the center of the variac. The contact tends to snap off leaving the end of the brass arm rubbing on the rotor and then things run really erratic.

Matrk

Posted by Monte L Fullmer (Member # 2797) on 12-31-2009, 01:01 AM:

I've had to replace three variacs on Alpha platters due to the same button wear on the rotor. You can really see the "Christmas lights" effect where that variac is mounted when that button is worn off .. and horrible platter action..

I think that you can replace that rotor instead of buying a new variac. Pair of external snap ring pliers removes the ring attached to the rotor, which will remove the rotor from the frame.

Check with your supplier on this option - this has to come from STRONG.

-Monte

Posted by Patrick Matthews (Member # 2705) on 12-31-2009, 10:40 AM:

Ok, checked electric zero and that wasn't the problem. So I obviously have a bigger one. I don't have much (read any) experience working the the variac. I have one totally intact that was removed by a tech a few years ago and I'm trying to take it apart to see what we are talking about before I go ripping the active one apart. I'm having trouble getting, what I guess is, the transformer out to get a better look at the brushes and whatnot. I can't seem to remove it from the casing because of the variac shaft, I'm assuming.

Can anyone help me out? Sorry for my lack of knowledge, but I'd like to try to get it fixed myself than having to drag a tech down here.

Posted by Louis Bornwasser (Member # 3063) on 12-31-2009, 11:11 AM:

As Monte mentioned, remove the shaft (set screws on "wrong" end) and then disassemble shaft using the ring-removal tool.

Now that the holidays are behind us, you could also ship the variac to one of us for repair. The part you need: the contact and contact plate are easy to deal with once you gain access. louis

Posted by Mark Gulbrandsen (Member # 72) on 12-31-2009, 05:49 PM:

Be wary of using the one the tech removed... it must have been removed for a reason... and why did he not repair it? Parts are cheap and available through STACO Energy Products or W.W. Grainger.