s7-1200 PLC going ON then just OFF power

Hello everyone,

we supplied a system to a client with a panel contains s7-1200 CPU along with digital and analog I/O cards, it was commissioned and working fine.
they called us for a problem they had when i went there thinking it's just a bug in the code but we found the following:

1- the PLC is OFF power even i measured 23.8 vDC n it's terminals but for a period of time it powers ON
for 2 minutes then OFF again. also when i removed the 24 supply wire for some time and then connect it again, the PLC powers ON then after 2-3 minutes, again OFF.

i supplied the PLC directly to the power supply and the same result.

2- they added s7-200 PLC to the panel by their own and i noticed that they made a "jumper" from our
I/O cards to their own s7-200 cards which they installed as a back-up so that signals will be distributed on both cards ( i think it's wrong but i need confirmation from experts - s7-200 uses 220 AC )

so what could be the cause ?

I have never met such a practice.
Did you tried to disconnect their "jumpers"? Try to do this and see if the problem is returning.

if it were me, remove their gear and observe the result. If it works the problem is with their gear and they need to troubleshoot accordingly.

From an OEM point of view the warranty is now void.

You have either a short or severe voltage drop. I second Janner10's suggestion, remove every wire off the inputs and outputs and power up the unit then if all is well put back your own wiring only and walk away. Make sure to send them a huge bill for your time, this way they will call you first before making changes.

madatix,
Did you solve this case? What was the problem?
I'm curious

yes, it was as we expected in the replies, and the customer's team took the hit and we are safe

thank you all