Sharp CD-BA120 Service Manual page 36

CD-BA120/125
(1) Focus-HF system check
Although a CD is inserted and the cover is closed, "NO
DISC" is displayed.
Press the OPEN/CLOSE switch (SW1) without inserting a
disc, and try starting the playback operation.
1. Did the pickup move to the PICKUP-IN Switch (SW4)
position?
2. Does the focus (lens) move up and down?
(Waveform drawing 36-1).
3. Is the laser lit?
4. Is the turntable rotating?
When a disc is loaded, start playback operation.
1. Is focus servo activated? (Waveform drawing 36-2)
2. Does DRF change from "L" to "H"?
3. Is the HF waveform normal? (Waveform drawing 36-3)
Stopped
CH1=500mV CH2=10V
DC 10:1 DC 10:1
FDO
1
T
DRF
2
TE
3
CH Position To
-3div -1div 0div +1div
=Filter= =Offset= =Record Length=
Smoothing : ON CH1 : 0.000V
BW : FULL CH2 : 0.0V
CH3 : 0.00V
CH4 : 0.00V
Figure 36-2
Yes
Yes
Yes
Yes
No
Is the disc rotating?
Yes
CH3=1V
500ms/div
DC 10:1 (500ms/div)
NORM:20kS/s
CH2
Position
0.20div
+3div
=Trigger=
Main : 100K Mode : AUTO
Zoom : 2K Type : EDGE CH1
Delay : 0.0ns
Hold off : 0.2us
Stopped
CH1=500mV
DC 10:1
T
FDO
1
TDO
3
=Filter= =Offset=
Smoothing : ON CH1 :
BW : FULL CH2 :
CH3 :
CH4 :
No
Sled motor (M2)
No
Check the focus peripheral circuit.
No
Check the laser diode driver Q3 peripheral circuit.
No
Spindle motor (M1).
No
Pins 1~11 on IC1
Check the laser diode driver Q3 peripheral circuit.
Focus error circuit (pins 20 and 21 on IC1)
No
Check the spin system.
If the disc is spinning and a HF waveform is generated,
DRF will go H.
No
If the level is not normal, check around pins 27~29 on IC1.
– 36 –
CH3=500mV 500ms/div
DC 10:1 (500ms/div)
NORM:20kS/s
CH1
v/DIV
500mV
=Record Length= =Trigger=
0.000V Main : 100K Mode : AUTO
0.0V Zoom : 2K Type : EDGE CH1
Delay : 0.0ns
0.000V
0.00V Hold off : 0.2us
Figure 36-1
Vp-p=1.0V~1.3V
0.5mV/div,0.5µsec/div
Figure 36-3