Kone Miprom HS Marathon Door issue

I have a Kone Miprom HS with a Marathon door operator that's having some intermittent issues. For whatever reason the elevator doors - on occasion - will not open when getting to a floor. Car will level into the floor properly and the arrival bell will ding, but the door will not open automatically. However the door DOES open when you press the door open button, or press the call button on that floor. I've ensured that the LU, LD, and DZ switches are working properly and that the magnets are properly aligned. I've watched the LEDs on the COP board and when it happens, and I can say the the car knows that it is floor level and in the door zone. The DO7 output (which is presumably for the door open command) does NOT come on until you press the door open button, and the DOL input (labeled D03 on the COP board) is in the proper state. Issue has been going on for a while now, and both the HLSB and COP boards have been replaced to resolve separate issues, but this problem has persisted through it all. LRE contactor has also been replaced, and the door operator has been relearned. Is the issue the main CPU board in the controller, or is it the door operator itself? I'm leaning towards the CPU board, as that seems to be what give the door open command, but

So on an HS like all Montgomery controllers, the open-door signal from the control is DO10, and DO7 is the door close signal. You need to see if the DO10 signal is coming on and go from there. I suggest you tighten connections, and pull the Molex connectors off and spray some cleaner on the pins and re-connect them.

Also, the DO10 signal goes into the Car Panel Connection Board, and if memory serves me the signal to the operator is a 115vac contact. Nen side of the contact is L1A and then out to the operator. Good Luck. Let us know how you make out.

Will try this on the next visit. I appreciate the feedback. Will post back here once I have results.