One of my fellow mechanics is having a problem with the car randomly going to different floors without any input such as car calls or hall calls. Sounds a bit strange to me. I was thinking that it could possibly be power supply problems. Any other thoughts? Thanks!

The power supply is definitely the place to start.

I've heard of this happening because its parked at a floor and loses DZ input, at which point the car thinks it's not at a floor, so it runs to go find one. I think in this case DZ magnetic switch was replaced, because the internal contacts weren't conducting well.

That's a great idea. I'll let him know to check that. Thanks for the input TC7.

Does the car run to a random floor after making a run, or does it just sit at a floor and randomly go to a floor?? Do the lights for car and hall calls light dimly on the cards? If the former, look into the closing sequence. First you get the gate signal, (X5 I think), then you get the door lock (X8 or X8a), then you break the DCL. I have seen x5 go high and then go low for a second, (dirty gate switch in Operator), get x8 and then get x5 aagain and this causes the car to run one floor (up if you have 4 slot cards and down if you have 3 slot cards.
If the latter, look for a bad ground. The board ground is the center tap on the transformer.

Thanks Johnny. Those are great tips. I will have him check into these.