Triplex Montgomery Miprom 21. Two of the three cars consistently travel past the top or the bottom limit and shut down. The one car has never done it. Supposedly the big K has spent several thousand dollars throwing parts at it. This happens at least once a week. Does not seem to favor one car or the other, it is both. Any ideas to start with? Thanks in advance.

What year was this system installed installed and what type of drive and brake are you using!

Please forgive my ignorance for not posting more. These were installed in 96. They are Digital DC drive, no gen sets. Has standard brake between gearbox and DC Motor. Thanks

I guess I would start searching parameters and looking at terminal switch settings that are different between the good car and the other 2...Any errors coming up on the fault logs.

I would check the the M contactors auxillary contacts, especially the normally open ones, i believe you will not get a pattern output to the drive if one of these contacts fails, it will pick the brake and drift. also i have had trouble with the small practically hidden relay called PR which picks up the M contactor. I have had this relay go bad a couple of times, and it will chatter the M contactor intermittently and make the drive unstable. also the DSD switch in the door operator will cause the M contactor to chatter if it is on the edge, any way you should get some error codes with all of these symptoms, one last thought is that you could have a bad drive board that is not triggering the scr's correctly, also make sure main line wiring is tight.

Are you getting no indications from the service tool (or World software) as to the status of the cars at the time of the "motion excuse" or "fault". you should have a fault log which will tell you what direction the car was demanded, the status of profile demand and more.....

I would also check fans on bottom of Allen Bradley drive...If thats what you are using!If they bind up or short they can give out really bad noise through out the system...

Thanks for the tips. We just took this on and it is not under contract yet, due to the building being owned by the bank. We have not hooked up the tool to it but will next time this happens. I will however go ahead and check the items listed by you guys. Thanks again. I will keep you posted.

I think Scott Davidson is right on. I've seen a couple of these cars setting in the overhead repeatedly. Turned out to be the auxillary contacts on the relay that picks M. Good luck.