Film-Tech Forum ARCHIVE: AW3 MUT spinning super fast on teardown

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Posted by Justin Hamaker (Member # 2165) on 12-29-2008, 02:30 AM:

Tonight I started breaking down a movie and things were fine for the first reel. But when I turned the motor on for the second reel, it started spinning at top speed right away.

There was nothing obviously wrong: motor works, belt is fine, connections seem to be fine, no indication of fried wiring, switches all seemed to be functioning fine. The only think I can think of is I recently changed the brushes on this MUT, but it's been used several times for tear down since then.

Posted by James Westbrook (Member # 3690) on 12-29-2008, 04:08 AM:

Is it one of those Bodine motors?
I had a platter motor on one of my AW3's surge into forward speed during breakdown, literally taking the reel back up onto the platter. I had to unplug the motor to finish tearing the movie down. I sent the motor off to Christie for repair, but was transferred to another theatre after that so I never got the diagnosis of what caused that motor to spin at top speed like that. Though this is a motor on your MUT, the problem sounds similar...

Posted by Monte L Fullmer (Member # 2797) on 12-29-2008, 04:21 AM:

Do you use the "Brake" switch when breaking down? If so, there could be a possibility that the circuitry in the speed control card on the MUT has shorted due to the sudden reverse of current when the "Brake" switch is engaged to reverse the platter motor, and this short is sending full voltage to the motor.

Even though it's a handy thing to have to slow down the platter, that "Brake" switch is the death to these MUTS due to the weak circuitry since the platter motor has to receive current from the MUT to slow it down.

I just use a rag to slow down the platter when the splices comes around and not touch that "Brake" switch.

-Monte

Posted by James Westbrook (Member # 3690) on 12-29-2008, 06:05 AM:

I remember being told to leave the Brake switch alone on those MUTs, too. I had forgotten that.

Posted by Steve Guttag (Member # 268) on 12-29-2008, 06:34 AM:

It actually sounds like the speed control module on the MUT has taken a dump...does full-speed situation apply to both make up or break down?

Steve

Posted by Tim Reed (Member # 137) on 12-29-2008, 07:10 AM:

Yep, that's a classic symptom: the speed control's shorted.

Posted by Mike Blakesley (Member # 26) on 12-29-2008, 09:28 AM:

quote: Monte L Fullmer
Even though it's a handy thing to have to slow down the platter, that "Brake" switch is the death to these MUTS due to the weak circuitry

Is that on newer AW3s? I have a 1980 model and have been using the brake switch on it from the start - never a problem. I think the switch has been replaced once or twice, but that's to be expected.

Posted by Damien Taylor (Member # 4255) on 12-29-2008, 09:58 AM:

Yeah, i'm using an AW3R, are the r generation in the clear of this problem?

Posted by Mark Gulbrandsen (Member # 72) on 12-29-2008, 10:09 AM:

It is indeed shorted but before you install a new $75.00 controler check the MUT motor carefully. You may find that it either has a very worn commutator, worn brushes or that it may be full of carbon dost. Any of these will also kill a brand new controller. NOw if someone grabbed a reel while it's turning that will also kill em. Mut motors can be rebuilt by any competant motor shop.

Mark

Posted by John Walsh (Member # 168) on 12-29-2008, 11:39 AM:

If I remember, the 'brake' switch only shorts the motor leads together thru a low-ohm resistor. It shouldn't affect the control card at all.

Posted by Steve Guttag (Member # 268) on 12-29-2008, 12:14 PM:

Yeah, there shouldn't be a problem with using the brake switch, though most seem to not use it properly. I've never had a blown MUT from it.

Now blown controllers...they have gone from time to time. Don't over torque things, it is bad for the film and the equipment.

Steve