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Section 2. Diagnostic Techniques
CAUTION
Switch off power before removing or installing SLD
cards. Use the correct probe tips when connecting the
oscilloscope or meter to the logic pins.
The 5444 may be taken off-line by operation of the
CE mode-select switch (see 2.2.1). AC and de power
remain on.
1.4 APPROACH TO SERVICING
Take the following approach to servicing the 5444:
1. Obtain the operator's report.
2. Use any error printout routine that the program of
the using system provides.
3. Run any available diagnostic programs.
4. Use the appropriate maintenance analysis procedure
(MAP)
charts,
which
are
contained
in
the
documentation of the using system. See 2.4.4.
1.4.1 Major Functional Areas
1.4. 1.1 Data Recording Area
Data-recording functions are provided by the following
areas:
1. Read/write heads.
2. Read/write electronics (four cards).
3. Unsafe-condition latches (three latches).
4. Upper and lower index transducers and amplifiers.
5. Disk surfaces.
The 5444 can neither detect errors in the recording area
nor recover from these errors, except to signal 'data
unsafe' to the using system.
1. 4. 1. 2 Access Area
Disk-accessing functions are provided by the following
areas:
1. Electronic control of mechanical motion.
2. Drive mechanism.
3. Track-crossing detector.
4. Home detector.
To prevent damage to the drive tire, circuits protect the
2-2
(5/70)
forward
and
reverse
clutches
from
simultaneous
energization.
Access errors occur when the actuator is directed to a
track but fails to correctly position at this track. The
5444 can only either signal 'access overrun' or stop at
track 000 and signal 'home'. If the carriage is driven past
the home position, either the R/W heads unload at track
minus 001 or the trip mechanically unloads the heads
before the carriage is fully retracted.
1. 4. 1. 3 Operational Control
Operational control is provided by the following areas:
I. Carriage interlock switches.
2. Head-load/unload controls.
3. Speed detectors.
4. Head-load interlock switches.
5. Cartridge inter locks.
Any errors in these areas de-activate the 'ready' line,
or fail to supply index pulses. Any failure of the speed
detector does not allow the 'cartridge safe' line to set.
1.4.2 Error Conditions
1.4.21 Unsafe Conditions
The unsafe condition is generated from the following
latches (see ALD page FN230):
1. 'Write unsafe' latch.
2. 'Erase unsafe' latch.
3. 'Read/write select unsafe' latch.
Mite Unsafe Latch: This is set by any one of the
following conditions:
1. Write operation is selected but no write transitions
are detected.
2.
Write operation is selected and multiple R/W heads
are selected.
3. Write operation is not selected but write current is
on.
Erase Unsafe Latch: This is set by either one of the
following conditions:
1. Write operation is selected but erase current is not
on.
2. Write operation is not selected but erase current is
on.
Select Unsafe Latch: This is set by any one of the
following conditions:
1. Read and write operations are selected.
2. Read and erase operations are selected.
3. Carriage is not detented and either a write or erase
operation is selected.
1.4.2.2 Not-Ready Conditions
The 'file ready' line indicates to the using system that
the 5444 is ready. A not-ready state may be caused by
one of the following faults:
1. One of the interlock switches has failed.
2. The rotational speed is less than 64% of full speed.
3. An incorrect head-loading sequence has occurred.
4. AC or de power has failed.
5. An unsafe condition has arisen.
6. The CE mode-select switch is not set to ON LINE.
1.4.23 Access Overrun Condition
The access-overrun error condition is signaled by 'access
overrun' to the using system. The signal is raised when
the carriage overrun interlock switch senses that the
carriage is too close to the center of the disk. The
sensing occurs at track 204/205* (5444 Models 2 and 3)
or track 104/
105~
(Model I only), and de-energizes the
forward clutch to prevent the carriage from driving
further forward.
1.4.24 Read/Write Errors
Read/write errors can be detected only by the using
system. The 5444 has no means of parity checking.
1.5 ERROR RECOVERY PROCEDURES
Figures
2-3
and 2-4 provide error recovery procedures
for use when a suspected head-to-disk interference (HDI)
has occurred or when R/W heads 02 and 03 are aligned.
See
4. 7 .1.3
for head alignment details.
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