We put two DI 8x24VDC ST modules on the end of an ET 200SP rack last month for a new guard on the stacker. IM 155-6 PN ST, twelve modules now, CPU is a 1516.
Door closed, everything reads fine. Open the door and all eight inputs on each of the last two modules go to 0 at the same time. The other ten keep working, the LEDs stay green and the diagnostics buffer is empty. I swapped module 11 with module 5 and the fault stayed with the position, and the door switch makes and breaks clean on a meter. One thing I noticed, the last two base units are a lighter grey than the rest, if that means anything.
Is the door switch pulling something down that I can't see? Or is that lighter grey on the last two base units telling me something, I think it has to be more than a colour.
What feeds the L+ terminal of those two bases, and is it the same 24 VDC as the rest of them? Trace it in words for me: from which supply, through which contactor, to which terminal on the base. Could be it goes through the safety relay's K1 K2 contacts.
Traced it. L+ on base 11 comes from terminal strip X4, and X4 is fed from the output side of the safety contactor K2, the one the door drops out. The other bases up to 10 come off X2, which is straight off the 24 VDC supply. The electrician who added them took the nearest terminal he could reach. Photo of X4 attached.
Two things it could be, a dead module or the feed, and your trace answers that. The lighter bases matter as well, the colour isn't a styling choice on these. Post the device view screenshot if you want it checked against the configuration.