Been chasing this gremlin for about 2 weeks. It is not consistent as in where in the hoist-way I find the unit down. She is faulting out on a 1021, inspection indicates an invalid I/O condition. In the normal operation inputs: CON3A-1 “INCTM” and CON3B-4 “INHAM” are high with 24VDC for it to run. However I find unit down with all 7 inputs: INCTU, INCTD, INCT, INCTU2, INCTD2, INHA, and INHAM are high.

I have checked wires from the car top, verified voltage on the S24-2 card and traced every plug back to the CWIK board in the car operating panel. I have found nothing. However if I unplug CONA or CONB from the S24-2 board this fault will appear. It’s almost like I am intermittently loosing voltage to the board.

Not sure where to look next.

Replace the S24-2 card

Had a similar issue the other day, had a "flakey" hoistway access enable switch.

Start by ensure that the 24 Vdc power suply has no drop voltage upper than 10% on the CN board, also verify the 120 ohm of the CAN end of the chanel 2 (car chanel) that is, on car side only the door board (udc) shoul has the CAN closed. After this perform a TECCR follwed by TECC in the IMS.

I’ve seen this exact problem (where you find all the IOs on the S24-2 card high) twice, both were a bad S24-2 card.

As a little public service announcement, it does more harm than good to re-teach CAN for an intermittent problem. If it ever works the boards know their configuration. Too often guys run these commands for no good reason and end up with more wrong than when they started. This is a perfect example. If he does the TECCR then TECC as suggested, and there is an HN riser, now you have no hall calls either. And if you’re really unlucky, there could be a brake in the teach line so you won’t have all your hall calls back until you go through the gutter and find the problem.

I used to have these problems on some elevators. The reason was wrong closing of the CAN end, the line impedance was too low due to having more than one 120 ohm resistor inserted on the car.