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Repair of stepper motor for color wheel feasible?

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Arjan van Gog:

Just wondering if someone can tell me if there's any point in trying to repair a stepper motor for a color wheel in my Martin RoboColor (original version) that appears to be failing. It's a KH42HM2-017 which I believe has been used in some other Martin products as well.

The problem is that it is no longer moving over the entire range, it will only  move so far. I've tried to 'excercise' it a bit with a chase going from 0-255 and back but no change so far. It doesn't seem to be stuck or anything, it just won't move outside that limited range but instead 'bounces back' to the beginning of that range. I can fairly easily move it outside that range by hand, even with the power on, and it will then stay pretty much in that new range.

I have no idea what its innards look like so I don't know what that says about the type of failure or if it is even caused by the stepper motor itself. Would opening and cleaning it possibly do any good?

I may have found a source for a second hand specimen for just 5 Euro so if I can still get that I'm not going to muck around with this one too much, unless cleaning it is likely to help.

I'm an EE btw but my practical experience with stepper motors is virtually non-existent.

Thanks in advance for any suggestions.

James Feenstra:
its usually cheaper to replace the motor than to try and repair it...once they go there's no real easy way to fix them

duane massey:
It's also possible that the problem is the IC that drives the motor.

Ray Cerwinski:
Not familiar with this innards of this particular fixture, but it almost sounds like it's homing incorrectly. Can you maybe swap a sensor or motor from the other color wheel just to narrow it down to a single component?

Arjan van Gog:
Well, I put the stepper motor in another fixture and it worked perfectly. Then I put it back in the original malfunctioning fixture and it seemed to work fine, at least for a while. Then somehow it got misaligned but after a recalibration (can be done using the DMX dimmer channel) it was back in line with the rest and is working perfectly. So at this point I'm not sure if it was the stepper motor after all (and to be honest the way it moved did suggest that the motor itself was fine and that the problem was with the control).

Maybe the connector had become corroded or something and the simple act of disconnecting and re-connecting it cleaned it up enough to allow proper signals to be sent to it again? I'm not sure if that could explain the kind of movement I saw though, it would move perhaps 20 degrees and then return to its original position and then would start rotating 20 degrees again. Actually it looked exactly as if the controller was simply ignoring one or more higher order bits (would fit perfectly with Duane's suggestion) but I really don't know enough about the design of this fixture to know if that is likely or not.

BTW There's no sensor associated with this color wheel, it's calibrated by letting it turn until it is stopped by a notch for that specific purpose.

I guess for know I'll just keep my fingers crossed and hope that it will continue to work. Thanks to all for your suggestions!


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