Siemens S7-400 Does Not Power On


Thread Starter

Abdul Mateen

Hi Sir,

I have S7-400 CPU 414-3 PN/DP which was working normal. But now when communication error appear at HMI, I found CPU powered off while power card is ok. I have replace CPU with new one, and system is ok now.
my question is:

how we can check the fault of removed CPU which was powered OFF?
there is any fuse inside CPU?

Gabriele Corrieri


there isn't fuses inside cpu.

At least I think you should found some (I've not checked) in switching supply for cpu (I think that the supply voltages for the cpu maybe created inside). check for electrolitic condender form factor.

Could be also a transistor for switching power supply.

How year old is the cpu? Here we usually send the faulty parts to a service repair (we have Siemens service and other 3-4 labs that give us a good service repairing)

Gabriele Corrieri