Film-Tech Forum ARCHIVE: Crompton-Greaves (RCA soundhead) motor failure

This is topic Crompton-Greaves (RCA soundhead) motor failure in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Christopher Seo (Member # 7) on 09-27-2003, 01:02 PM:

Help!

My theatre runs RCA 1040s and Century Cs. The RCA soundheads have Crompton-Greaves motors on them. Everything was running fine until the last changeover of the night, when I flipped the motor switch and the motor just sat and hummed, moving at about 1 frame per second. Frantically spinning the inching knob didn't help at all.

The motor had been running fine all day, including when I ran down the leader perhaps 20 minutes previously. Earlier in the day, it did possibly feel a little stiffer than usual to turn over, but that seemed to go away.

I un-coupled it from the soundhead; it still just stalls or moves extremely slowly, even with help. Voltage at the terminals is a normal ~117 VAC. I don't know anything about motors, so please, any suggestions are appreciated!

Detailed motor specs:
Crompton-Greaves
BS 170 Frame B56
0.25 HP
1440 RPM
110/115 Volts
5.4 Amps
Single Phase
60 Hz
Continuous Rating

UPDATE: Please see my third post.

[ 09-27-2003, 02:55 PM: Message edited by: Christopher Seo ]

Posted by Darryl Spicer (Member # 711) on 09-27-2003, 01:07 PM:

Does this motor use motor brushes in it. If so there may be a large accumulation of dust inside the motor or worn brushes that need to be replaced. There also may be a problem with the motor start voltage to get the motor moving.

Posted by Christopher Seo (Member # 7) on 09-27-2003, 01:45 PM:

AFAIK there are no brushes. It's just a regular induction motor, I believe (if that precludes it having brushes).

Posted by Mark Gulbrandsen (Member # 72) on 09-27-2003, 02:30 PM:

Most likely you have a bad start switch or start winding. Twisting a piece of small rope i the correct direction around the inching knob might get it going with a stready pull on the string to get it running near speed first, just be sure the start switch is not stuck in the ON position or the start winding will literally fry! Most motor shops will laugh at you when you take a motor like that in for service, but persistance will find a shop that will repair it for you. We have a great local guy in SLC that can repair even the old LeLand motors on the Simplex 4 star sound reproducers. He modifys both a new start switch and the motor end housing so the new switch will work. There are people like him in every city and persistance in looking will find someone near you as well.
Mark @ CLACO

Posted by Christopher Seo (Member # 7) on 09-27-2003, 02:53 PM:

Thanks for the ideas guys. But apparently there was a simpler cause....

UPDATE: When I got the motor on the workbench, I noticed a loose wire leading into the windings... the bare end was stranded copper but obviously very old and corroded with green powder (we're three blocks from the ocean). After checking the other motor it seemed likely the wire had come loose from one of the terminal posts. Stuck it back on and voilà, it works again!

My question is now... do wires just, say, corrode and break loose like that? AFAIK that terminal hadn't been touched in years. And... how do I prevent further problems until we can get a spare motor? Re-strip the wires? They all look pretty fragile....

Posted by Gordon McLeod (Member # 33) on 09-27-2003, 03:52 PM:

tere is a lot of vibration inside a motor that over time loosens connections and breaks down the varnish insulation

Posted by Mark Gulbrandsen (Member # 72) on 09-27-2003, 05:23 PM:

Common now Chris, that motor is from the 1930's!! It has every right to corrode and come apart after nearly 70 years of service [uhoh]

Mark @ CLACO

Posted by Bruce McGee (Member # 131) on 09-27-2003, 06:41 PM:

Had the same solution for a bad 1940 era GE motor on my Holmes 8. The wire that connected the start winding to the start switch simply rotted away. I crimped a new length of wire to the solid wire end and it has worked great for 3 years.

Being the age that it is, I also cleaned every inch of the insides of the motor, and lubed up the bearings and cleaned the switch contacts. Runs like new!

Posted by Ken Layton (Member # 133) on 09-27-2003, 11:10 PM:

There is an old motor repair shop in Centralia, Wash. that has repaired several motors for the RCA soundheads. They have the ability to make new start switches for them. These folks do excellent work and they prices are very reasonable.