Puzzle for Siemens S5 EXPERTS!!

I have an S5 135U PLC that is loosing inputs to the CPU in as small a time frame as one scan, I.E., the E-stop input should always be on,
I 0.0, unless of course the E-stop circuit is open, I have ran a pigtail from the E-stop controller to another PLC to make sure it is indeed a PLC problem and NEVER loose it on the other PLC, an S5 115U.
I am loosing inputs from different input cards, not just one, as I set up test inputs from spares. The card order in the main rack is CPU, a WF706 encoder card, 4 input cards, 4 output cards (3 regular output cards and 1 relay card, then an expansion card for an ET200 unit that runs the control panel. Is there a way to troubleshoot the problem to the defective component, or is it a swap solution till it goes away, I have already replaced the CPU, power supply, and the PLC rack, and the first input card. Help!!

Ready... FIRE!... Aim... never-mind...

could one of your inputs be causing it to drop out? or if it's more than one card, i would say it could be loss of the common somewhere. we have a machine in our shop that we put plc's in like this and we can shoot them into the sun.

Maybe the problem is with weak contacts in the front connectors in the i/o cards.
They contacts are spring loaded, so that can get weak over the time.

I bet you didnt exchange the front connectors when you exchanged the i/o cards.

I think this may be a little joke from Mr Woods.... look at the date of the original post....

D**n.

Got s**ckered
(again, some will say).

sho is taking them a long time to fix it, been down for almost 3 years?