My answer is very simple--from your 1st picture,  you have NCU problem. Don't think HMI issue , fix NCU 1st:

Try like this :

#1--, set your NCU switches S3 to 1 S4 to 3 , then power up NCU to see you can get PS Led flash slowly and PF led keep on and display "6" -if yes do next step, If No take picture post here--(if you get same picture like you post here, you may need your NCU send to repair)

#2--followed 'Yes" answer from #1, flat screwdriver set S4 from "3" to "2" then back to "3' --you need to see PS quick flashing then keep on and PF is off. --then set S3 to 0 S4 to 0,

you need have +5 V Green on and PR on. at this time if you cable is good, you should get back to communication NCU to HMI, then load your NC/PLC back

biggz

Hello,

Im the operator and service tech of a Hegescheidt u2000 wheel profile lathe.  Our Sinumerik 840D machine has 120202 fault and is unresponsive with runtime error 28, "not enough stack memory".  Leading up to this we were seeing 2000 PLC sign of life fault. 

See NCU pic, PF led is flashing. 

MMC 2.22   CNC 2.13   PLC 2.17

Appreciate any assistance.

Hello biggz,

My suggestion to you is please check you have valid NC & PLC data back up files (.arc) either on your MMC or on external storage device before following steps suggested by expert nulizhang

Hello,

User should archieve data or back up data after successful commissioning or if any modfification in PLC or NC data. Data back up should be carried out when system is healthy & not during fault condition. So please check if you have back up data on any external storage device.