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Topic: Trouble with a rewind table

James R. Hammonds, Jr
Jedi Master Film Handler

Posts: 931
From: Houston, TX, USA
Registered: Nov 2000

posted 03-27-2002 09:09 AM

This is the Kelmar RTV 8900.

The problem here is when I raise the speed to get the spindle going.
With no reel to weigh it down, it wont start spinning until the speed adjustment is at about 20-30%, and with a reel weighing it down it wont spin until about 50%.
When it does start spinning, it jerks and jumps immediately to whatever speed the control is on.
Ive tried looking at all the connections and everything seems ok.
Anyone have any ideas?

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 03-27-2002 09:12 AM

Yes, remove, inspect, and carefully re-insert the motor brushes. You may find that while they aren't worn out they may have hung up in their holders instead of making good, spring-loaded contact with the motor commutator. Taking them out and reinserting them may correct the problem.

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Ken Layton
Phenomenal Film Handler

Posts: 1452
From: Olympia, Wash. USA
Registered: Sep 1999

posted 03-27-2002 09:20 AM

Also check the rheostat (speed control) for a wiper contact that may have fallen out of it's holder.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 04-03-2002 03:42 PM

Now it's my turn. It's a Kelmar RTV-8500. I went through the sticky motor brush business a few months ago and it's been fine up until yesterday. Symptoms: Running hot, motor obviously (and odiferously) overheating. Finally, it blew the table fuse.

I took the motor out. It turns but maybe a bit tighter than would want. I took it apart. No signs of any damage or shorting. The commutator was worn where the brushes contact it (I polished it a bit). Bearings seemed fine. I blew out a lot of carbon dust. Brushes are getting short but still seem servicable. I checked for grounding between commutator and shaft but found none. I did find continuity between all segments but I think that's normal. Put it all back together. Seems like it tightens up to some extent then but I'm not sure if that's what is causing the overheating. Any ideas? BTW, I measured table input at 3.5-3.8 A at full speed with belt in place but otherwise no load.

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Ken Layton
Phenomenal Film Handler

Posts: 1452
From: Olympia, Wash. USA
Registered: Sep 1999

posted 04-03-2002 06:07 PM

Could be shorted turns on one of the motor windings.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 04-03-2002 08:50 PM

I'm beginning to think that may be the case. More a matter of "there isn't anything else there" -- permanent magnets, two bearings, brushes, commutator & armature. Brushes are running a bit sparky but I don't think that's going to make a motor overheat. I thought maybe a bad diode in the bridge rectifier could have been letting AC through but they seem to check out ok.

Is there anyway to diagnose shorted windings besides the process of elimination?

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 04-03-2002 09:05 PM

The Kelmar RTV 7000 series I used for many years went through several variacs. THe brush on the back of the control would lose contact.

I don't know if the RTV 8900's have variacs or some electronic control.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-03-2002 09:24 PM

I'm voting on a bad motor on Steve's case.

John, yes they still use variacs...though the 8000 series rewind tables use a larger variac than the 7000 series.

Steve

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"Old projectionists never die, they just changeover!"

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 04-03-2002 09:42 PM

Come on Steve, it's just moving up in the world. From rewinding film in the booth to front-of-the-house Smell-O-Vision work.

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Stan Gunn
Expert Film Handler

Posts: 176
From: Clematis, in the hills near Melbourne Australia
Registered: Aug 2000

posted 04-06-2002 05:19 AM

To check the armature windings you need a good ohm meter, connect the leads to the brush holders and slowly turn the armature.
this will give you the dc resistance of each winding, sparking at the comutater could be the comm out of round causeing the brushes to bounce.

hope this helps.

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ALL PARTS FOR VICTOR AND KALART VICTOR 16MM PROJECTORS.SERVICE TO 35 AND 16MM PROJECTION EQUIPMENT.
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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 04-06-2002 08:43 AM

I get about 9 ohms on all opposing commutator segments, suggesting it's not shorted, which is strange since the process of elimination was strongly suggesting that. But the commutator was extremely worn under the commutator, like maybe a third of a mm. I'm trying to turn it down. The other clue was that the motor was harder to turn than it should be, despite nice, easily turning ball bearings. I was able to get it to run last night without overheating with it held together by its own friction (leaving out the long bolts) so I may be on to something. A replacement motor, while costly, is not as bad is one might fear, given the price of the table, so when I get bored with this "project" (a time rapidly approaching) I'm just going to give up and get order one.

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