Digital Equipment RW504-ZA, Service Manual

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• There is only one failed component. Simultaneous failures of unrelated items
are not considered possible for purposes of this test.
• Service will be done, if necessary, if a problem is found (i.e., the unit does not
have to be left in a ‘‘clean’’ state).
The test takes advantage of this and does whatever is necessary to determine
the cause of the failure. Disks are not intentionally rearranged, but if the
picker starts this test with a disk in it, the position and orientation of that
disk is unknown.
When an error occurs, the cause may be the power supply, cables, drive
electronics, motors, encoders, belts, gears, sensors, or picker. No assumption
is made about the integrity of any of these components. To isolate the actual
cause of the failure, a process of elimination is used.
The components are tested in a sequence that starts with the most basic functions
and builds to the more complex, and interrelating components (i.e., the motors
cannot be tested if the power supply is dead).
Whenever the initialization sequence is run, FIND HOME is attempted. If the
‘‘home’’ position cannot be found, the FRU isolation test is run automatically.
When the FRU isolation test is run from the control panel, the FIND HOME
sequence is run.
4.5.2 How to Use the Results of the Internal Tests
Similar to treating symptoms rather than the real problem, the suspect FRUs
given by the FRU isolation test may actually mask the root cause of the problem.
The hard move error that caused the autochanger to run the FRU isolation test
may have only been a PRODUCT of the actual problem. Blindly and repeatedly
replacing the suspect FRU(s) will not solve the problem.
4–12 Troubleshooting and Diagnostics