Programmable stepper control help please

I posted the message below in SEB and then though that maybe it should have been posted here too. So here it is, slightly modified: I recently acquired a programmable stepper motor controller. It was made by Richmill Manufacturing Company Ltd. around 1982. It is designed to drive a unipolar stepper motor. The guy I got it from said it worked fine when he put it away and then upon trying it about a year later it only works intermittently. I did discover one wire in the cable that goes to the motor does not have continuity. This wire is one of the two common wires that are the center taps of the motor windings. I do not have the motor. I do not have a schematic and so far have not been able to find one. I have not applied power to it yet. It has a 3.6 volt ni-cad battery that is used for memory backup and it needs to be replaced. I need advice about replacing electrolytics. Though none are bulging they are old and have not had power running through them for a long time. Should I just replace them as a preventative measure? I have heard about "re-forming" electrolytics. Should I even bother trying this? There are only about

10 of them so they would be cheap to replace. Another question is would it be safe to try to power up and run the control without connecting a stepper motor? Looking at the board I see that 4 MOSFETs are used to switch rectified 50 volts AC to the motor coils. I thought about just trying to turn the thing on and trying to program it and see if it at least thinks it is doing something. Since I don't have any large steppers I thought about connecting a 12 VDC 500 mA power supply in lieu of the rectified 50 VAC to the circuit board and using a small unipolar stepper to test the controller. Finally, what I would like to do is connect the controller to a circuit that would convert the unipolar switching signals to step and direction so that I can use a Geckodrive servo amp and a servo motor. This way I can run whatever size motor I want connected to an indexer that I am building. Thanks, Eric P.S. Since posting the above message I got to wondering how one goes about testing whether an electrolytic capacitor is good or not. I have an Extech DVM that has a capacitor measuring function. Is that a feature that might help? If the measured capacitance is within 25% can I call the cap good? Thanks again, Eric
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Hello, again. That is a really old board. I remember playing with those things about that time and recall the motor driver chips were really flakey. May I suggest researching the motor driver chip and see if you can find any info relating to problems with that particular chip.


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Paul Drahn

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