Kone wanted an absolutely huge amount of money for an MX 20 that was water damaged. Much, much more than you have stated. We removed it, rewound it, replaced the bearings, and re-installed it. Then did the construction/commisioning start-up, resolver angler, tach polarity, tach voltage, shaft learn, adon learn, brake adjustments, full loadweighing calibration, etc, etc. When we were done, we had a fine running machine! We did it for far less than half of what $ Kone wanted. The customer was convinced that the MX20 was a space ship, wound by aliens, and defied analysis! We proved them wrong, and will do so again. Elevator brothers all over the world contributed much to this effort, thank God!

When we were done, it would roll back, (roll up) on each and every stop. I got scared for an instant, thought "OH, sh*t, somethings' wrong with the rewind". But I don't get scared so much my mind turns off. I'm gonna keep punching until either I win, get k/o'd, or the final bell sounds. It's just an elevator, after all, just nuts and bolts, and wires. It's not a UFO. We can learn, we can understand, we can fix it. We have the technology!

It would come to the floor very controlled, in the normal way. Then the brake would set, and the drive contactor would drop out. During that instant, the car would roll up an inch or so. All the helpful experts were focused on brake issues, and who could blame them? It was the most probable cause for the problem. After exhausting all brake adjustments and remedies, I started to suspect the timing of the brake drop. (But meanwhile I got pretty good experience adjusting those brake pods! Heh heh!)

The drive board has little LEDs, that say "Contactor", and "Brake" on them, and the brake led indeed would go dark first, (just like it did on a good running car), meaning that the motor would hold the car for just a sec, while the brake mechanically set. And indeed, they were sequenced correctly. The only problem is, that with an oscilloscope, you could see that the command from the drive board to the main brake module wasn't crisp and definitive, and since it was going grey, rather than going to 0 volts, the brake module wouldn't set quick enough. On one channel on the scope, you could see the command to drop the brake, and on the other channel, you could see the command to drop the main contactor. The brake command out of the drive board feeds into the brake module. The character of this command is important. It doesn't like a "roll off", rather, it needs a crisp sqaure corner to the drop of the pick command. The brake command WAS going low, before the main contactor command went low, and the brake WAS setting, (and setting hard at that!). We had the sheave so clean, and shoe gap so low, ...everything so clean....it couldn't possibly be the brake itself. But it wasn't setting fast enough. (and not for a mechanical reason) Although the LEDs on the drive board showed the drives' intention of dropping the brake, before dropping the drive power to the motor, it wasn't so. Can't let the LEDs fool ya....

This delay in the drop of the brake coil voltage provided just a little window of time for gravity to pull the counterweight to the earth, making the car roll up an inch or so. Changing the drive board fixed the problem.

The roll back problem wasn't related to the motor work, just incidental. Another weird thing was this- While the water-damged motor showed 0 or 1 ohms to ground, on all three legs, the drive current limit would allow a bit of current flow, before crowbaring itself off. Then it would turn on, then off, then on, at a fast cyclical rate. This set up a staccato mechnical pounding, both in the motor, the car, the control, everywhere. This might have introduced spikes and noise, that stressed the drive board, causing it to have problems. That was actually almost more interesting than changing the motor, fixing that brake timing issue. That's why I love my oscilloscope! Can't see that sh*t with a meter.

Here's my thread on it at ElevatorShack, a European elevator site. I also posted it here, but I think this thread has more pictures. Early on, some of those guys actually said that only Kone could do it. But we made beleivers out of 'em!

http://elevatorshack.com/forums/index.php?/topic/3257-how-do-you-remove-a-kone-mx-20-flatmotor/