Film-Tech Forum ARCHIVE: Potts Platter Puzzler: Arm pooped, won't drive Motor!

This is topic Potts Platter Puzzler: Arm pooped, won't drive Motor! in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Tim Reed (Member # 137) on 07-11-2007, 02:28 PM:

Here's one that's got me. Type 3 Alpha 5-deck platter. The very bottom arm (you know, the easiest one to work on!) won't run any motor that's plugged into it. The motors all work fine on the other arms, but no matter which motor you plug into the bottom arm, it won't go.

The arm WILL work (i.e., drive a motor) on makeup, however, but not on rewind or payout. I've already installed a new selector switch, thinking that's about the only thing it could've been, but I was wrong. The AMP pins are in excellent shape and fit snugly to the motor plug, and in the connector itself.

I have continuity from the variac, through the column, through the selector switch, to the motor receptacle... and I EVEN HAVE VARIAC VOLTAGE all the way to the end of the line at the motor connector.

However, the variac voltage disappears when I connect a load (a motor) to the motor receptacle on the arm. The voltage on the other arms is unchanged; it just drops to zero on the bottom arm. I remove the motor plug, and there's my variac voltage back.

I've had the arm off the column and could find no shorts or opens, so I'm stumped as to where to look next. Anyone had a similar problem?

Posted by Kenneth Wuepper (Member # 1174) on 07-11-2007, 08:28 PM:

Tim,

I would look for a high resistance in the feed system to the motor. The clue is that there is voltage present with the small load of the meter but that drops to nothing when a load like the motor is attached. Perhaps a loose terminal or rosin solder connection in the circuit.

KEN

Posted by Mark Gulbrandsen (Member # 72) on 07-11-2007, 09:51 PM:

Ken is on the right track. When I worked as a bench tech I wold see this effect from time to time and its usually from bad solder connections or an open resistor... in your case probably a bad crimp or connection... pinched wire, etc.

Mark

Posted by Louis Bornwasser (Member # 3063) on 07-12-2007, 10:48 AM:

We've had several bad connections on the multi-pin plug inside the arm/column. In one case, one pin was too small (different series of connector). Louis

Posted by Tim Reed (Member # 137) on 07-12-2007, 11:32 AM:

Thanks, guys! Will keep looking.