prochpe4

[snip] My machine (Sinumerik 840DI) stops its process after some time. However, it does not report any error code. [snip]

what exactly happens when "Stops in process"? Does the system hangs? i.e. does not response to any keys when pressed on MCP or OP? Does all LED LITS/flashes from MCP? Does the system reboot?  

prochpe4

[snip] My idea is to connect it to a laptop using USB. However, I suppose I need to install a diagnostic program/tool on my laptop. Does exist any diagnostic tool for Sinumerik 840DI that could be installed on my laptop??

[snip]

HMI Advance sw on separate desktop is available which user can load on external PG/PC. But please note, it is commissioning tool & not much useful for diagnostic. User can view system screen on separate desktop & it works on MPI interface & not on USB. Please refer this link for more detail information on HMI advance software tool.

Hope this helps.

prochpe4

[snip] Can this happen in the middle of process?

Yes, it could happen. Please check 24 V DC power supply at PCU, any momentary drop or dip or ripple in PCU 24 V DC power supply might trigger such problem, also try by replacing DC power supply, (do you have UPS power supply for PCU, if yes please check its battery voltage)

If all above points are OK, then I suggest you to get PCU 50 along with MCI card (it is installed inside PCU) tested/repaired from Siemens service/support center only.  

Hope this helps.