Booting the Siemens PCU 20 and PCU 50

When booting the Siemens PCU that you have installed, it should be a relatively simple process, but there can be some problems that come up, so we wanted to go through a few to help anyone who is having issues. When the power supply is switched on, the PCU boots automatically. The system software is installed in the factory and is ready to run. The basic display appears on the screen if the MMC has booted successfully

Problems With Booting

PCU 20:
If the PCU 20 cannot make a connection with the NC, the message: “wait for NCU-connection:”x” seconds”, “x” = 1 to 60 appears. If a connection has still not been established after this time, then rebooting takes place soon after. Check the following:

  • Is the NCU module ready to operate? (digit “6” on status display)
  • Is the MPU cable instered, is cable attached properly to connector?
  • Are other MPU notes (MSTT, BHG, …) interfering with MPU communication. (open links for testing)
  • If the RESET button of the NCU was pressed again during boot (e.g. as performed during a software upgrade [position 1 / general PLC reset]), the control system must be switched off and on again before the PCU can be booted successfully.

PCU 50:
If the PCU 50 does not boot (screen remains dark), the 24VDC power supply must be checked. If the power supply is present at the power unit on the PCU 50 and the seven-segment display on the rear panel does not light up, then the PCU 50 is defective.

If the PCU 50 boots, but cannot establish a link to the NC, then “Communication
to NC failed” is displayed in the message line at the bottom. In this case, please

check the following:

  • Is the NCU module ready to operate (digit “6” on status display)?
  • Is the MPI cable inserted, is cable attached properly to connector?
  • Is the baud rate in the Start-up/HMI/operator panel front menu set correctly? It must be set to 187,5 baud (password for protection level 2 required).
  • Are other MPI nodes (MSTT, BHG,…) interfering with MPI communication.

    (open links for testing)

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