Sharp DV-560H (serv.man6) Service Manual ▷ View online
21
DVD-Series
4. Spindle Servo
●
Rotate the disc under Constant Linear Velocity (CLV).
●
Control is necessary to make quick invariable line speed when making a pick-up move when
in the seek mode.
in the seek mode.
Invariable rotation on MO/HD a For making faster access
CLV
CLV
a For changing the disc rotation speed depending on the
pick-up position (faster on the interior side (1400rpm)
and slower on the exterior side (580rpm))
and slower on the exterior side (580rpm))
5. Automatic Power Control (APC)
●
On laser, the amount of light being emitted changes greatly, even when the running electric
current only varies slightly. Therefore, the amount of omitted light is detected on the Photo
Detector in order to monitor and control the stability of the laser current.
current only varies slightly. Therefore, the amount of omitted light is detected on the Photo
Detector in order to monitor and control the stability of the laser current.
4-2 How to Make the Error Signal
1. Optical System of Hologram Pick-Up
LD
PD
(monitor)
Pa
i
I/V
Conversion
Signal
Monitor PD ··· Adjusting the
amount of light
emitted by laser
emitted by laser
Laser
Hologram··· Leading the reflection light
from the disc to the targeted PD
Disc
Signal Layer
CL (Collimator Lens) ··· Making parallel light
OL
Raised Mirror
PD
22
DVD-Series
2. How to Make FES (Focus Error Signal)
· · · Hologram Foucault Method
Note: The following PD form is slightly different from the actual one. (image only)
C
B
A
D
+
–
–
+
+
–
–
+
–
–
(At the time of just focus)
No
error
(Close to the disc)
(Far from the disc)
Actual form has I/V amplifiers here
●
From the deviation of focus, the light shown above (black part) comes back on PD. By
receiving the output through a differential amplifier, DC voltage, which responded to
defocusing, is output.
receiving the output through a differential amplifier, DC voltage, which responded to
defocusing, is output.
3. How to Make Thread Error Signal
Take out the low frequency component for tracking error signals.
Tracking Error Signal _ LPF _ Thread Error Signal
With this, move the thread to make OL stay around the free neutral point.
Tracking Error Signal _ LPF _ Thread Error Signal
With this, move the thread to make OL stay around the free neutral point.
PU
OL
When thread does not move.....
Bump
23
DVD-Series
4. How to Make Spindle Error Signal
●
Due to CLV control, error signals come from the reproduction signal.
DVD: approx. 580rpm ~ 1400rpm CD: 200rpm ~ 460rpm
A
B
C
D
+
Reproduction Signal
(after 2 values)
VCO output
The VCO same wave number is low.
Increase it with the phase comparison error signal.
Increase it with the phase comparison error signal.
Then
Found the phase!
PLL lock
PLL lock
The VCO same wave number is high.
Decelerate the spindle motor with the phase comparison error signal.
Decelerate the spindle motor with the phase comparison error signal.
Locked
X'tal and VCO
(immediate 5 reproduction signals) locked.
After all, the disc is rotating
at the regulated line speed.
X'tal and VCO
(immediate 5 reproduction signals) locked.
After all, the disc is rotating
at the regulated line speed.
The VCO same wave number is low.
Increase it with the phase
comparison error signal.
Increase it with the phase
comparison error signal.
A
B
C
D
AGC
EQ
Asymmetrical
Revision
Signal
Spindle
Error Signal
Reproduction Signal
X'tal
Error Signal
VCO
CLV Spindle Error Signal
27MHZ
Phase
Comparison
PLL
LPF
LPF
Amplifier
Phase
Comparison
VCO output
X'tal output
<Wave shape Image>
24
DVD-Series
However....
VCO
Reproduction Signal
Reproduction Signal
Locked
If the disc rotates
at half speed...
at half speed...
No phase error comes out, so it is locked.
Cap Challenge of PLL is narrow
Because of that ···
Rough Servo is needed at the start
Rough Servo is needed at the start
There are many reproduction signal lengths.
DVD
3T ~ 14T
_
T means 1 cycle of the channel clock. 3T means 3 times as long as
CD
3T ~ 11T
that.
Because the length of T is different even for the same 3T, pulse
lengths are different.
A CD is approximately 6 times as much as a DVD.
lengths are different.
A CD is approximately 6 times as much as a DVD.
●
Measure the lengths of the minimum and maximum reproduction signals, then switch to PLL
operation after it almost reaches the targeted number of rotations (after getting in the cap
challenge of PLL)
operation after it almost reaches the targeted number of rotations (after getting in the cap
challenge of PLL)
Starting
Rough Servo
PLL Control
Measure the minimum pules
Measure the maximum pules
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