problem in S5 155U

1. Coordinator CPU (6SE5 947 3UA22) replaced by spare one.
2. Backplane of all Racks cleaned and reinserted all cards.
3. Replaced one output module (6ES5451-4UA13) by spare one, because one out put was permanently high.
4. Replaced all digital input modules one by one.
5. Deleted all input address from DB-1, one by one.

1. PLC goes in to STOP mode with BASP indication, immediately after downloading OB1 block.
2. PLC comes in RUN mode after erasing the user programme.

Please suggest what to do next

1) FDB1 ==> Error in DB 1

Data block DB 1 contains the list of digital inputs/outputs (P peripheral

with relative byte addresses from 0 to 127) and the interprocessor

communication (IPC) flag inputs and outputs that are assigned to the

CPU.

DB1 is mandatory in multiprocessing. FDB1 could indicate that a CPU is not detecting its assigned periphery.
Try to load only DB1 and no other program, to see if DB1 is problematic. Check if defined periphery is available.

2) UPROG ==>STOP mode caused by user program
SYSFHL STOP ==> mode caused by system error (may be caused by

user error, e.g. overwriting system RAM with a block

transfer or similar (when a system error is marked, a

four-digit hexadecimal number/error code appears at the

bottom edge of the screen - refer to RS 75 in Chapter 8).

SYSFHL STOP seems also to correspond to what you describe.
No program, CPU runs ==> no HW problem as such in first place.
I believe that some pointer (indirect addressing) is miscalculated in the application, and overwrites the header of a block. Try to activate if possible the program part by part. To isolate the problematic part.

You can speed up your search using the info in the system data 75
Try to find out more detail with the sytem data 75 where the error is located.
Chapter 8, page 8-26 of theprogramming manual.
http://support.automation.siemens.com/WW/view/en/1087149