Usually you have a requirement of removing the duplicate records from a file using SORT with the option SUM FIELDS=NONE
If the requirement is to always have the first record of the input file (out of all duplicates) in the output file, then the EQUALS option will help you in doing it.
EQUALS option preserves the order of the records being read from the input files.
So your SORT card will look like.
SORT FIELDS=(1,80,CH,A),EQUALS SUM FIELDS=NONE