The usual locations of the tune files do not apply with the 5977. If you suspect you have a corrupted tune file and you need to reset, rename the tune file in D:\Masshunter\GCMS\1\5977 to atune.old, or the appropriate tune to .old .
A fresh tune is located under C:\GCMS\MSSETUP\5977 . You will find the tune there as atune.u etc. The tune file needs the polarity set by opening manual tune and saving the tune file with the proper polarity.
Atune.nu and atune.pu no longer exist.