IBM 5531 Operator's Manual page 85

Problem Determination Procedures
Test 600 - Diskette Drive
(continued)
6. Did the following appear on your screen and is the drive type correct?
YES -
Press Y; then press the Enter key. The SYSTEM UNIT 600 message appears
briefly when the system has completed this test successfully. Continue with the
next test.
NO - Have the system unit serviced.
5-600-4
Operator's Guide