Digital Equipment RW504-ZA, Service Manual

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determines the type of error recovery scheme to employ. This tailored technique
provides gentle, stable control of the mechanism, resulting in increased reliability.
6.1.2 Mechanics
The mechanics consist of the following major assemblies:
• Leadscrew assembly
• Picker/carriage assembly
• Mailslot (disk loading and ejecting assembly)
The picker/carriage assembly is the heart of the mechanism. This assembly
positions disks in front of storage slots, drives, and the mailslot. The picker
inserts, removes, and flips disks. It also activates the mailslot mechanism.
The carriage/picker assembly includes active payload electronics that are similar
in design to a plotter’s. A single-axis plunge is used since the picker does not need
to travel horizontally (translate). The picker electronics include the picker motor
with a ribbon cable connecting the motor to the carriage and the autochanger
controller PCA.
The disk insertion slot, referred to as the mailslot, accepts a disk (inserted
shutter-end-first) and rotates the disk 180 degrees. This allows the picker to
grasp the rear of the disk and insert the disk shutter-end-first into the drive or a
storage slot.
The carriage motor rotates the carriage leadscrew, driving the carriage. The
motor also monitors the amount of movement with a built-in encoder wheel.
6.2 The Autochanger Controller PCA
The autochanger controller PCA contains the following major components:
• Microprocessor
• Motor Control Chip (MCC - Interface between the processor and Pulse Width
Modulation)
• SPIFI Chip (SCSI bus control)
• ROM
• RAM
• Pulse Width Modulation Amplifier
• Front Panel Control and Filament Drive
• SCSI Interface
6–4 Theory of Operation