CP1005. cannot connect to it via Ethernet cable

Error A0-03-4301 means that the peripheral module in the CP-1005 unit has stopped communicating with the processor. This can be caused either by a fault on the module or by interference that can enter the system either through the power supply or the bus. In this case, it is not enough to restart the system, it is necessary to turn off the power. If the system crashes every time the power is turned on, it is likely that the module is faulty. If the problem is caused by interference, it might help if you connect the negative pole of the power supply to the chassis of the switchboard.

Even if this error occurs, it is still possible to connect to Foxtrot from the Mosaic environment. In the header of the Mosaic screen on the toolbar, the status of the PLC is signaled by yellow color with Error label. When you click the mouse, a description of the error is displayed. It should also be possible to connect via the SetPlcIP tool. But you cannot be connected from both programs at the same time. Maybe the reason is in this point. IP addresses are set correctly according to your description. There is no problemn in this.

Now I try to use this CP1005 at office and also cannot connect to it neither via Mosaic nor via SetPLCIP (Of course I don't use them at the same time). Error A0-03-4301 does not disappear after PLC power reboot (I tried it a lot of times). And, at office, I have another CP1005 that is connectable (with same network parameters) from my PC. So, Ethernet port of my PC works correctly.  

Thus, if I understand correctly the peripheral module of CP1005 is faulty. Or there is something else I should check before making such conclusion?     

Yes, it seems there is any hardware problem in PLC. When you plug an ethernet cable, LED diode ETH turns on or is it still off? And if it lights, does it blink regularly or non- regularly? When LED is off even with plugged cable or LED blinks regularly, it means a problem (PLC repeats sending a message and doesn't get any answer). During a common communication ETH LED blinks non-regularly.

When the internal peripheral board does not work, there may be, for example, a problem with the power supply, with the internal converter that provides voltage for the internal circuits of the PLC. This would explain both the peripheral module and ethernet interface problem.

When I plug ethernet cable into PLC, LED indicator lights and blinks regularly, but seldom (in others PLCs, when communication with PC is correct, that LED blinks often). What is a reason of this peripheral module and ethernet interface problem and how can we avoid that (even after problem solving we should execute some precautions to avoid it in future)?

As I wrote, there can be for example a problem in power supply circuits of PLC, you can measure 24 VDC on power input terminals but the voltage somewhere inside is less than it should be and some circuits won't work due to low voltage. It may be caused when some condenser is damaged etc. You can' avoid it anyhow. A capacitor may be damaged, due to wear and tear or aging. But no one can tell you the exact cause without having a technician look at the PLC boards.