Two buttons on keypad stopped working

[Cyltech]

We have an Okuma MX-55VA mill with a OSP U10M controller that has been functioning perfectly, but suddenly the "Edit Aux" and "Preferences" buttons stopped working out of the blue. Not intermittent, just completely stopped working. Everything else on the machine and on the control panel functions fine.
When the machine starts up, the LED's on those buttons light up, but the buttons don't switch to the required settings pages or give an audible beep when pressed.

I've taken the controller apart to trace the issue to my limited ability and it's not the physical buttons themselves. There is voltage coming to the switch terminals, the switches function electrically as usual, and I've traced conductivity into and out of the board that houses the switches, through the switch and the corresponding diode. The problem is more likely in some IC on one control board or another which must have died, preventing the control signals for those 2 buttons from reaching the computer.

The board that is likely at fault is marked "PANEL IF 4 (A911-2353)"
but I'm not sure if the problem might rather lie on another board in the control box marked "MPMN (A911-2196)".

Has anyone had this happen before? Buying a replacement controller board is on the table, but I'd be interested to know if anyone has had this problem before and if it got fixed by swapping the board out?

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[Algirdas]

You did a big job locating the fault. What I would do before replacing the module I would swap the keyboard channels in order to see if the fault is address or data related. Next, I would check for standard ( not Okuma made ) chips on board and check if it's reasonable to replace them.
Next, there are microswich ( DIP switch ) modules on the board, I would check the functionality as weel, because these are responsible for the action of push buttons ( keyboard keys ) there.
That's really very rare with Okuma controls. I had once a bit simillar problem after replacing the pannel ( The client asked for interface language change ) and that was just a couple of "wired" configuration contacts on the board.

[OkumaWiz]

Turn the key that locks out the edit and parameters. Problem fixed.

[Cyltech]

Well, I'm not gonna make excuses: I completely overlooked the key locks. It was a key that had been turned to edit lock.
That's straight up embarrasing, but the problem is fixed! Thanks!