I have had the same thing happen, carbon gets packed into the nook and crannys of boards. after a good dusting and blow job on all my boards and the problem when away. I prob shot some air into the amps as well.

How many times have you heard that before.... 😉

Hey green pants, I had to go to this job today for same problem, only lasted one day this time, I pulled boards and removed all carbon like u suggested, will wait and see, thanks

i spoke too soon after 6+months my 401 with the same problem trapped someone at 5am. car was in the pit on the limit. i found that the car had DIRF's and LCF's and the car was rolling forward 6"+ in the up direction. looked at the LW% and it was at 0. after i got the guy out i hopped in the car with a couple of engineers and the load cell never went up in %. repair crew will be headed out with a new cell and weights ill let ya know how it goes.

Hey green pants, gotta love that name,! The elevator gods must have heard you on this forum and decided to let you know they are always in control. I can't tell you how many times during my 25 years as a mechanic that when you ask about a troublesome job, it seems to breakdown soon after. Very strange indeed. The last time it happened I was having lunch with the guys and asked about a job I had helped him on a few weeks earlier, he said it had not broke down since we worked on it, I said great, guess we fixed it. About ten min later dispatch calls with a occupied on the same car, very strange indeed.
Anyway back to business, my 401 went into pit on Monday, I swapped the CPU, and it ran til Friday morning and is in pit again, today I swapped out transducer I/o board. I spent all day Tuesday and most of wednsday running the car and checking on different items, it ran like a charm. I guess I will replace one item at a time till problem is resolved. Will keep u posted

Well I am not having any luck with this bastard 401 elevonic car, it continues to go in the pit. I have replaced all controller boards and power supplies. I have verified the initiation switch is working properly. the car ran 10 days before going occupied in the pit with 4 people inside. I logged on to the omt and the 200-6 test indicates the car is 00 out of service, 13 normal operation. i checked the position and it was below floor in finals at 9.2 feet. there were no abnormal conditions in the 200-4 test. just jumped out finals and car comes out of pit and back into service. The occupants were coming down and the car just went into the limits. the last things to change are the cop1 board. I could change encoder or ppt but i dont think this is problem. Greenpants, do you have any other ideas? Im going to change cop1 board with another car, but i dont think this is the problem.

PPT= Primary POSITION transducer....Id be looking at that, you can test the PPT and PVT via the OMT.

Do you have the OMT manual for the 401

You could try running the 230 velocity and ppt test. It tells you if they are way off but it runs to slow to look at the encoder properly. I would put a new encoder and coupling on they tend to only last a couple years. Also have you swapped your transducer I/o board and adjusted it properly? The cop1 is pretty old but I can't imagine that's it because it was in motion going down, not a load cell rollback problem. Check your ppt locking nut and wiring and verify your first floor level is 10.0 ft. And that your tape isn't riding up on a sheave. Ever looked to see if your TM cam roller is still there?

thanks for the reply greenpants, I have ran the 230 test a few times both velocity and ppt test and every test is right on the money. I have swapped every board in the controller plus power supply with another car. the bottom floor is exactly 00A0. I was on the cartop repairing the initialization switch as it would not make up when car was above the bottom floor, causing car to initialize up on a POR. the roller was there and the tm switches were opening fine at the bottom. I thought i was on to something after fixing the initialization switch as the car ran 10 days before occupying into the pit on a down run. Here is something maybe you know about, I was researching the manual looking for a clue when i came across the 40 test for the test log. I reset the log, and after it went occupied i looked at the log again and noticed FE64, PCF was at 35 counts, and FE74, VMODE5 was at 35 counts since the log was cleared 3.5 days ago. PCF position control failure? there has been no complaints of car acting up except when it goes into pit, but 35 times in 3 days and 5800runs indicates something is up. could it be the ppt is intermittently failing. or is this a result of VMODE5 which i cant find any info on.

PCF is position control failure
Vmode5 is a timed slowdown and stop that is due to the pcf.
Knowing what you have changed I would look to your power amps and feedback circuit. Megging your motor and gen fields. I'm sure you have made sure all your brushes are in good shape. Your ppt knew it was in the pit so I wouldn't think it was that. If you have a pvt change it. No other faults were on the 40 test? If you didn't know you should record the fault log40 test and 200-2 and 200-4 before you kill the power.

Is there any chance that a problem with load weighing would cause this problem

it shouldn't run down into the pit from another floor even with a bad load cell. i had a car that did go into the limit but from the first floor rollback.

Update on 401 trouble, hey kiwinightstalker I do have a omt manual, the company I work for is owned by Otis. Any way, i replaced the pvt 8 days ago after last breakdown, and no failures yet, iwas going to change cop1 board, but Otis does not have any spares, repair only so I opted for the pvt. Just have to wait and see, thank goodness for the break though as I have been swamped with other intermittent calls. Hopefully it is fixed, or maybe the elevator gods are just giving me a break from this 401 car.