IBM 5150 Hardware Maintenance Manual page 113

Position the System Unit Power switch to OFF. Partially
remove the Logic Printed Circuit Board, leaving all the
connectors on except P-6 (See Section 3, "Removal/
.Replacement.") Lift the Logic Printed Circuit Board just
enough to observe the Head assembly. Move the head away
from track O. Power the System Unit on, and observe the
head assembly motion.
Track 0
f'.
\
Track 39
f'.
DOES THE HEAD ASSEMBLY MOVE TO TRACK 0 AND
THEN AWAY FROM IT BEFORE THE END OF THE
POWER ON SELF TEST (POST)?
NO
Replace the Diskette Drive assembly. See Section 3,
"Removal/Replacement. "
YES
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