Hi sir:
Possibles fault
One EAK is missing in the plug-in unit
There is one EAK too many in the plug-in unit.
2. Fault of the differential inputs.
Wrong output on input/ output IC.
Upper loop test terminated with fault (it is possible that the
plug-in contacts X1E, X1A, X2E, X2A on the EAR got mixed
up).
Lower loop test terminated with fault (it is possible that the
plug-in contacts X3E, X3A, X4E, X4A on the EAR got mixed
up).
3. Initial state of input/output IC incorrect after reset.
Fault when writing, reading test pattern on input/output IC.
Filter times for inputs incorrect.
Incorrect interrupt generation via inputs.
4. Faulty output latch of internal control.
Fault when reading, writing to internal register.
Defective timer flip-flop.
Timer defective.
Blessing