A B757-200 AVIONICS TECH NOTICES A DISCREPANCY WITH THE MM PROCEDURE FOR THE HF DATALINK SYSTEM. THE REQUIRED SELCAL CHIME OR LIGHT DID NOT OCCUR ON CERTAIN ACFT AS NOTED IN THE MM TEST PROCEDURE.

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ON FEB/XA/08; FURTHER TESTING OF OTHER ACFT DISCLOSED TO ME THAT I OVERLOOKED AN AMM ITEM CALLED OUT FOR ON THE TEST. THE ACFT TEST WAS NOT PER THE AMM (NO SELCAL CHIME OR LIGHT OCCURS). I HAVE TESTED SEVERAL OTHER ACFT AND DETERMINED THAT THERE IS NO SELCAL CHIME OR LIGHT PER THE AMM. THE HF DATA LINK SYS ON ACFT XXX DOES FUNCTION NORMAL; BUT THE AMM IS INCORRECT. I HAVE SUBMITTED 5 ENGINEERING REQUESTS TO CHANGE B757 AMM TO REFLECT THE PROPER TEST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THEIR COMPANY ENGINEERING JUST RECENTLY ISSUED AN ENGINEERING ORDER FOR CHANGES TO THE HF DATALINK SYSTEM TEST PROCEDURE. THIS CHANGE INFORMS MAINT THAT WHEN PERFORMING THE HF DATALINK TEST; TO VERIFY THAT A 'LINK TEST SUCCESSFUL' MESSAGE APPEARS ON THE MCDU. NO LIGHT OR CHIME WILL OCCUR. BUT; ENGINEERING ALSO NOTES THAT SOME ACFT MAY STILL HAVE EITHER A LIGHT OR CHIME HAPPEN. ACFT WITHOUT THE LIGHT OR CHIME TEST RESPONSE HAVE THE NEW INTERNAL SOFTWARE THAT HAS BEEN MODIFIED.