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DC Motor runs briefly then quits.

Rob_Feature

Rob_Feature

Rob Feature
I know this is an audio forum and I'm temped to not tell you what I'm even working on (in order to keep the question general) but who knows..maybe this will help: I picked up a Sankyo Sound 500 Super 8mm film projector but it had no power cord...so I'm trying to get it running.

The important focus here is about the DC motor that runs the mechanical processes of the projector, and I know there's lots of gurus here who could answer my general questions about what I'm seeing.

The motor is described as a "Frequency generator servo DC magnet motor (model MLN-25A)"

As mentioned, I didn't have a power cord when I bought this, but inside the unit is a transformer, so I'm assuming the power coming in is just standard household AC. The thing is, the plug connection is kinda funky...just two simple (round) male posts like this:

IMG_5565.JPG

I got this unit free and I found a standard AC cord that plugs into this successfully. So...I figured it would 'just work'. I plugged it in, the unit's lights power up, etc. However: the DC motor that runs everything (immediately after being plugged in) will run for about a half second...then it quits. It doesn't budge again until I unplug/replug the power cord.

I read elsewhere on the Googles that there could be a 'protect' in the transformer (or the motor?) that will kill the motor if the wrong voltage is detected.

That led me to look at the transformer. I noticed the input from the power cord has 2 voltage markings that seem odd to me: 100v and 117v (pic):

IMG_5566.JPG

I'm suspecting that my power cord is feeding in the wrong voltages, even though I can't really envision how a cord for this would do otherwise.

At this point I'm:

1. Trying to determine if this is indeed the problem and
2. Trying not to spend $30+ on a power cord just for this unit (which is what i see them for online)

So...thoughts on all this? Does it seem like the behavior is a 'protect' type thing...and do those input voltages on the transformer give any clues or seem odd?

Thanks for any input and help in advance (the gurus here never cease to amaze me!)...I'd love to get this up and running without popping for a really expensive power cord made just for this unit!!
 
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Also, as a followup...I'm finding a decent amount of corrosion throughout this unit, so it hadn't been used in a while. The motor indicates a manufacture date of 1976, and the power runs from the transformer thru a circuit board. All that makes me wonder if the board needs a recap (I wont do it unless I must!). Although the fact that the motor runs for a second, then quits until power is removed makes me still think a protect circuit is most likely the cause. Just not sure how to troubleshoot that, I guess.
 
Woah! OK, I'd delete this thread if I could but I think I figured it out. As I degunked things further and further, it seemed like the time the motor would run before quitting got a tiny bit longer each time. I kept hitting parts of it with detoxit (that stuff is magic) and it got better and better. I think a protection circuit was the cause..but it was kicking in because the motor couldn't push the gears (due to gunk), so it killed the circuit.

I have it running for much longer at a time now...seems to be the ticket. I'll keep cleaning..and thanks for a place to think out loud about problems like this. (maybe sometime somewhere someone will come along, find my post and get some inspiration). Thanks audiokarma just for existing!!
 
arts said:
The 100 volt winding is for use in Japan.
Click to expand...

Right, and is contingent on which tap of the transformer is connected to the AC supply inside the unit. The power cord itself is immaterial other than being the conduit between the wall and the projector.
 
Get some straight sewing machine oil or equivalent inert stuff if you can get to the motor bearings if not sealed, i.e. you can see the motor bearings thru a small hole. couple drops or so.

No pics? Getting where they ask questions and like a swami we have magic answers. I do know a spell for giving somebody constipation.
 
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