Digital Equipment RW504-ZA, Service Manual

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6.4.2.2 Read and Write Channel Electronics
Read channel electronics take analog data from the optical head and convert it
into digital ‘‘transitions.’’ These transitions are decoded by the decoder electronics
on the controller PCA in order to extract data from format and error correction
features. The write channel electronics take the serial data stream from the
formatter/sequencer and convert the digital pulses into analog data. This analog
data is then sent to the optical head.
6.4.3 Mechanism Assembly
6.4.3.1 Loader Mechanism
The loader mechanism consists of two motors: a spindle motor for speed control
and a loader motor for loading and unloading of the cartridge. The loader motor
includes a gear train and rack-and-pinion system that allow the cartridge shuttle
to raise and lower the cartridge within the loader housing. The bias magnet
subassembly sits on top of the cartridge shuttle and provides the correct polarity
for erasing or writing data.
6.4.3.2 Optical Head
A major feature of the optical head is a ‘‘split optics’’ design. This design
physically separates the laser diode and its associated detectors from the focus
/fine position actuators. This design results in a significant seek time performance
advantage due to less mass on the moving portion of the optical head.
There are several actuators in the optical head. The coarse position actuator
moves the focus/fine position actuators to the vicinity of the desired sector on the
optical disk. The fine actuator makes small corrections (+/-25 tracks) to center the
optical head on the desired sector. The focus actuator then moves up and down to
provide optimal focus on the light beam. All these actuators, and the laser diode
(and its detectors) are controlled by the servo PCA.
The laser diode and its associated detectors are part of a flex circuit on the optical
head assembly. On this flex circuit are analog electronics which further condition
the control signals for the laser diode, and preamplifiers for the servo and data
control signals that are returned to the servo PCA.
6.5 Optical Disk Layout and Error Correction
Two optical disk formats are available. Optical Drives in the RW504/RW524 can
read from and write to 650-Mbyte optical disks. The RW524 optical drive can
read from and write to both 650-Mbyte and 1.3-Gbyte optical disks. The target’s
role is to manage the 130mm multifunctional drive and disk as an optical memory
device through its SCSI interface. These optical drives support 130mm rewritable
optical disks conforming to ISO/IEC 10089 Format A, and write-once optical
disks conforming to ISO/IEC DIS 11560, for 650-Mbyte capacity. The RW524 also
6–10 Theory of Operation