s5 100U Istack

cottagewood

Member
Join Date
Oct 2005
Location
Kent
Posts
177
I wonder if some one could help me understand the Istack in a 100U.
I have a 103CPU which is in stop mode. I disconnected all the expansion except for 1 and fitted an input card and output card. I deleted all the blocks and did a CPU reset. It still wont go to run mode.
With the switch in the stop position I have an X below STOANZ, NEUSTA, BATPUF, ERAB, RLO and PEU
With the switch to the RUN positon it's the same with the additon of an X under STOZUS.

It's a few decades since I set one of these up but I can't see why it wont run.
 
PEU is your problem

• Expansion module not connected
• I/O bus malfunction
• Maximum length of shift register exceeded
• Module unknown
• Module in wrong slot

I've encountered failed bus units in the past, more than once.
 
I was pretty sure that PEU is the problem and I did exactly as you said, put just 1 expansion module with 1 io card. I have 3 cpu's and I've tried them all but no luck.
I leaning towards thinking all 3 cpu's may be faulty.
 
It's the same but i would expect that because the manual says one module must be connected on 100u otherwise the PEU error will be on.
I tried several different bus units and no luck
 
Last edited:
Yes, i did all that and there's no memory module.
The only concusion i can draw is that the 3 cpu's we have are all faulty.
 
Customers mostly only do that when it breaks, I've been telling them for years.

The problem was they had managed to blow every bus module, (15)
 
Yep, I had replaced bus modules 3 times for the same client in 2 different PLC racks. That was when I first learned that these "passive" devices can fail. The first time, I spent a long time swapping I/O and even the CPU before I decided to try replacing the bus modules. Ended up being the one next to the CPU thankfully, because I was going from left to right. Keep in mind the HMI has to be considered in any upgrade. The models that were capable of talking both to the S5 and S7 from Siemens are pretty much obsolete now.
 

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