Digital Equipment RW504-ZA, Service Manual

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The error (4D) and suspect FRU gave an AREA to look at when troubleshooting.
Visual inspection (concurrent with physical checks) helps to link the suspect FRU
with the root cause by providing an area to examine. In the preceding example,
the components that INTERACT with, and DRIVE the picker are examined.
Table 4–3 lists each error code and procedure for finding the cause of the error,
using the autochanger’s suspect FRUs as a guide. Error codes and recovery
procedures are grouped by functional area in the autochanger.
At the BEGINNING of the list of errors for each functional group, you will find
general HINTS about what areas should be checked when errors appear in that
group. Be sure to check out those hints.
4.5.3 The FRU Isolation Test Sequence
The following list traces the execution of the FRU isolation test. A failure
requires additional tests at that point to determine the actual cause. The original
sequence is not continued if a test fails.
1. Look at the error code generated by the FIND HOME sequence. Some codes
may have obvious, implied FRUs. (eliminates optical sensors and their cables)
2. Run autochanger controller PCA tests that do not cause host communication
loss. (eliminates power supply, power supply cables, ROMs, RAM, motor
control IC, and microprocessor)
3. Check that the motors are capable of moving by attempting to move them
very small distances in both directions. (eliminates motor assemblies (except
belts), motor cables, PCA drivers)
4. Pull picker fingers back. They should come to a hard stop with the leadscrew
nut completely at the end of the leadscrew. (eliminates the picker belt)
5. Move carriage/picker assembly toward the drive. It should come to a hard
stop. (eliminates the carriage belt)
6. Move carriage/picker assembly away from the drive. The move has to be
far enough to be certain that the leadscrew can move, but not so far that
a jammed cartridge will cause the test to fail. (eliminates the carriage
leadscrew assembly)
If the FRU isolation test has been run from the front panel, the FIND
HOME sequence will automatically be executed at this point.
7. At this point, there is some level of confidence that the system is capable of
moving the carriage/picker assembly. Using the new information learned by
running these tests, look at the error codes, the move ID that failed, and how
the recovery system failed.
4–14 Troubleshooting and Diagnostics