HP Surestore 160ex - Optical Jukebox, Service Manual

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Theory of Operation
Optical Drive Mechanism
Chapter 6 6-23
T
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the cartridge shuttle to raise and lower the cartridge within the loader
housing.
Bias Magnet
The bias magnet subassembly sits on top of the cartridge shuttle and
provides the correct polarity for erasing or writing data.
Optical Head
The optical head assembly contains both mechanical and electronic
components and is a “split optics” design, which physically separates the
laser diode.
The actuators and laser diode (and associated detectors) are on a small
PCA on the optical head assembly. The main components are as follows:
• Auto Laser Power Control (ALPC): Controls the intensity and
duration of the laser beam for erase, write, and read operations.
• Focus Servo (Fcs): Controls the vertical motion of the objective lens to
focus the laser beam on the disk surface.
• Fine Tracking Servo (Trk): Controls the horizontal motion of the
objective lens to follow the track of the disk.
• Linear Motor (LM): Positions the actuator in the vicinity of the
desired track on the disk.
Errors
The various error thresholds are the basis for deciding whether or not to
spare a sector. This could happen during the certification process (i.e. the
slip sparing algorithm) or auto-reallocation during a SCSI Write
command (i.e. the replacement sparing algorithm). These error
thresholds are related to the format of a sector in the User Zone.
Each sector in the User Zone consists of the following:
• Header
• User data
• Parity bytes for error correction
Each header consists of three copies of the sector's track number, sector