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Entry type: FAQ Entry ID: 45479931, Entry date: 10/19/2010

Why does the SIMATIC IPC not start up after voltage ON or why are computers or computer components damaged when turned off?

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When you switch on the SIMATIC IPC, it does not start or switches off immediately. If devices/components or plug-in cards with their own power supply are connected to the SIMATIC IPC interfaces, this can lead to so-called regenerative feedback into the SIMATIC IPC. Regenerative feedback can under certain circumstances damage the SIMATIC IPC or the internal computer components.

The component responsible for the regenerative feedback has to be determined by a voltmeter. If you are qualified accordingly, you can determine the component responsible for the regenerative feedback by measuring the voltage at the output connector of the PC power supply unit. You must note the following points to be able to detect a counter voltage in the measuring process:

  • The SIMATIC IPC must be switched off and the mains connector must be connected.
  • All the components of the plant that are connected to your SIMATIC IPC must be switched on and active.
  • If you determine that there are several components that might be the cause of the regenerative feedback, then connect only the component to be checked in each case separately to the SIMATIC IPC.

Possible causes for the regenerative feedback:

  • PCI-104 modules with additional external power supply (e.g. metrology modules, frame grabber card with camera connected).
  • External power supply on the 5V supply via a USB interface not in compliance with the USB specification.

Possible culprit components
USB I/Os with their own power supply:

  • KVM switch with USB and PS/2 interface to the SIMATIC IPC.
  • KVM switch with USB interface to the Panel.
  • USB hard disks.
  • Optical drives with USB connection.

As far as possible, operate components without external power supply or use components that do not have an external power supply.

Generally, regenerative feedback is not permitted for any SIMATIC IPC and must be prevented in all cases by the operator.

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