Tracking Servo; Spindle Motor; Audio Block - Sony CDP-CX235 Training Manual

search voltage with an amplified FE voltage. The FEO output is sent to a
current driver IC. This IC drives the optical assembly's focus coil to main-
tain focus on the disc during playback.
The FE and RFO waveforms can be used in troubleshooting to determine
if there is a signal output the optical assembly. The FOK test point can be
used to determine if the quality of the two signals is sufficient to find focus.

Tracking Servo

Once focus is found (FOK goes HIGH), the spindle motor starts and the
tracking servo loop is closed. The tracking servo moves the objective
lens so the laser can follow the disc's information track.
The center of the disc's track is identified using optical assembly detec-
tors E & F. The RF Amp converts these two input signals into a track-
ing error (TE) correction signal that is sent to Servo Control. Servo
control amplifies the TE input and closes the servo loop switch, output-
ting the amplified tracking error signal (TEO).
Servo Control
RFO,
FE
TE
The driver IC that receives TEO supplies current to generate a magnetic
field in the tracking coil. The coil moves the objective lens (with laser
beam) so the beam follows (tracks) the disc data.
Optical
TEO
Driver
Assembly
TE test point
RF Amp
33

Spindle Motor

Like the focus serve, the spindle motor servo has two modes of operation.
As soon as focus is found, the spindle motor is kick started and runs to
approximately the correct speed. This is the first mode of the spindle
motor operation.
The second mode comes some time later after the tracking servo oper-
ates. This is when the RFO data is reliable and can be used to govern the
spindle motor speed. This second mode of operation cannot be seen
because the motor is already running. However when the motor is linked
to the disc data, the LOCK test point goes HIGH.
Servo Control
E, F

Audio Block

Once the spindle motor is locked to the data (LOCK = HIGH), the data is
reliable enough to be audio processed. The disc data comes into Servo
Control as RFO. It is error corrected, digitally reconstructed and output
as a digital signal to the rear panel jack. The digital signal is also con-
verted to analog within Servo Control and delivered to the rear panel L &
R jacks.
While audio is output, the front panel display is receiving the CD track and
playback time information. Servo Control sends Sub Q digital data (and
clock) to Syscon for compiling and interpreting. The resultant information
is sent to the FL Display Driver as Data, Clock and Latch signals. The
Display driver determines what display segments of the tube have to be lit
to produce the desired time and track characters.
Lock
LPF
RF
FE
Amp
RFO
Spindle
M
Driver
Optical
Assembly
A-D
detectors