Spindle Servo - Sony CDP-CX235 Training Manual

E, F
RF Amp
Optical
Assembly
When the tracking loop is broken, the TE waveform changes from what
looks like .5Vp-p of noise to a large broken waveform of 1.5Vp-p (Ch 2).
The RFO signal shows losses of RF where the laser is crossing tracks.
P M 3 3 9 4 , F L U K E & P H I L I P S
c h 1 : p k p k = 1 . 2 8 V
c h 1
c h 2
1
2
C H 1 1 . 0 0 V = S T O P
C H 2 ! 5 0 0 m V = M T B 1 . 0 0 m s P K D
Defective Tracking Servo Waveforms
Channel Signal Name
1 RFO test point
2 TE test point
Time base = 100msec/div
Scope ground is taken at Vc (IC103/pin 12)
An open tracking loop is not common and is usually caused by foreign
objects in the optical assembly, its ribbon cable or a bad driver IC.

Spindle Servo

Even though the spindle motor turns the disc, its servo loop may not be
closed. A defective spindle motor servo produces RFO data that alter-
nates between good and bad (even tough they both look the same on the
scope). Looking at the LOCK test point at the Servo Control tells you if
the spindle motor loop is closed, since the focus and tracking servos must
TE
Servo
Control
FE (start)
TEO
c h 1 +
Location
IC103/pin 16
IC101/pin 13
49
work before the spindle servo can close. For example, if the tracking
servo were defective, the spindle servo loop cannot close because the
RFO data is unreliable. Therefore the other servos must be checked prior
to this check. It also takes a while to process the RFO data to establish
a spindle motor lock so the spindle servo is the last servo to engage. This
is shown when comparing RFO (Ch 1) to the LOCK test point (Ch 3).
P M 3 3 9 4 , F L U K E & P H I L I P S
ch1
T
ch2 1
ch3
2
ch4
3
CH1 2.00 V=
C H 2 ! 5 . 0 0 V =
4
C H 3 ! 5 . 0 0 V =
C H 4 ! 5 . 0 0 V = C H P M T B 2 0 0 m s - 2 . 2 8 d v c h 1 +
CD Playback Starting
Channel Signal Name
1 RFO
2 FOK test point
3 LOCK test point
4 C2PO test point
Time base = 200msec/div
Scope ground is taken at Vc (IC103/pin 12)
If all the other servos check OK and the LOCK test point remains LOW
(spindle servo defective), the common cause is the motor itself.
Spindle servo
lock
Location
IC103/pin 16
IC101/pin 24
IC101/pin 25
IC101/pin 19