46
Optical
Assembly
A, B, C, D
Outputs
RF Amp
Servo
Control
RFO
FE
FOK
10. Watch your scope as you apply AC power. If the FOK line goes
HIGH, focus has been found. The transition from search to servo
is then performed within Servo Control. At this point you know the
laser is working and the focus driver part of the IC is good enough
to achieve FOK. The following waveform compares the RF output
to the FOK signal. This waveform shows RF signal goes HIGH as
soon as focus is found. (The spindle motor also starts when FOK
goes HIGH producing the RF waveform that follows.)
ch4
ch3
ch2
ch1
CH1 2.00 V=
CH2!5.00 V=
CH3!5.00 V=
CH4!5.00 V= CHP MTB 200ms- 2.28dv ch1+
1
2
3
4
T
CD Playback Starting
Channel Signal Name Location
1 RFO IC103/pin 16
2 FOK test point IC101/pin 24
3 LOCK test point IC101/pin 25
4 C2PO test point IC101/pin 19
Time base = 200msec/div
Scope ground is taken at Vc (IC103/pin 12)
If FOK does not go HIGH, increase the scope’s time base and look at
the RFO signal for a rise in voltage as the lens repeats the focus search
operation in this test mode. NO RFO means there is no signal from the
optical assembly. This could be because there is no laser light or no
power (ribbon cable). If there is an RF output during focus search, yet
there is no FOK signal, the source of the FOK signal can be checked.
FOK comes from the RFO signal that is derived from the optical detec-
tors A-D. When the RFO reaches a set threshold, FOK goes HIGH
proving that there is light returned from the information of the disc (laser
and focus OK).
RFO can be compared to FE to see if there is an output before condemn-
ing the optical assembly. If there is an output from both, the optical
assembly and RF amp IC are OK and the likely suspect is a defective
Servo Control IC that makes the FOK signal.
An easy way to see if there is RF under this defective condition is to
repeat the Search operation. In the ADJ Test Mode, press the front
panel CHECK button. This CHECK button just repeats the search
operation, but the servo operation that normally follows will be inhibited
so the disc will not play. Place a scope probe at the RFO and FE test
points.
ch2
ch1
CH1 1.00 V= PKD
CH2!2.00 V= MTB2.00ms- 3.10dv ch1+
1
2
T
S Curve focus Search (Changer is in ADJust Test Mode)
Channel Signal Name Location
1 RFO test point IC103/pin 16
2 FE test point IC103/pin 14
Time base = 2msec/div
Scope ground is taken at Vc (IC103/pin 12)
11. Remove the jumper wire between the ADJ test point and ground.
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