Bose Life CD5 Series I Service Manual page 10

CD TERMS
Tracking Gain: The overall loop gain of the tracking servo. This controls how tightly the laser
is held in the center of the track. If the gain is too low, the player will have trouble with vibration
and eccentric discs, especially during track access. If the gain is too high the player will have
skips or mistracking with voids and scratches. Proper alignment is a compromise between
these two performance parameters.
Focus Gain: The overall loop gain of the focus servo. This controls how tightly the laser is held
in focus. If the gain is too low, the player will have trouble with vibration and warped discs,
especially during track access. If the gain is too high the player will have skips or mistracking
with black dots and scratches. Proper alignment is a compromise between these two perfor-
mance parameters.
Technical Terms
RFSM: RF SUM. The amplified A+B+C+D signal from the laser pickup.
Eye Pattern: The pattern displayed on an oscilloscope when monitoring the RFSM test point.
Jitter: The extent to which the zero crossings of the eye pattern occur at other than their ideal
times.
Focusing: Before a disc can be played, the player must focus the CD mechanism by changing
the distance between the lens and the surface of the disc. This must occur before the disc can
start rotating. If the player fails to achieve focus, it will retry. This occurs four times in the CD5
before it "gives up" and indicates "no disc" by lighting up the disc icon in the display.
TOC: Table Of Contents. The innermost area on the disc where track and time information is
stored. When a new disc is inserted into a player (i.e. when the door switch is opened), it must
read the TOC before the first track can be played.
CIRC: Cross Interleave Reed-Solomon Coding: The error detection and correction scheme
used on CDs to provide immunity to small scratches, etc.
CLV: Constant Linear Velocity. CD players rotate the disc at a constant linear velocity of 1.25
M/S. The angular velocity changes from about 500 RPM down to 200 RPM as the disc plays
from beginning (inside) to end (outside).
EFM: Eight-to-Fourteen-Modulation. The format in which the digital data is recorded on the
CD.
Photo Diode: The receiving element that translates the modulated light beam into electrical
signals.
Subcode Q data: The track and time information read off the CD.
Three Beam System: The most common system for providing focus and tracking error signals
for the respective servos. A three beam system uses a six element photo diode array, with the
elements designated A through F. The A, B, C, and D elements are located in the center and
read the information as well as supply the focus error signal. The E and F elements are located
on either side and provide the tracking error signal.
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