FOSO
FMSO
TRSO
DMSO
A B C D E F RFO
IOA
LDO2
LDO2
MD11
Switch circuit
APC circuit
Main axis control
detect circuit
Main axis electric machine
Feed electric
machine
Cn101
D5954
MT1389
Disc in/out
circuit
TK-
TK+
FC+
FC-
SL+
SL-
SP-
SP+
1
23
6
26
15
16
14
13
17
18
12
11
Figure 3.2.2.1 Servo circuit block diagram
2. Working principle
After power on, machine displays “OPEN”. After loading disc, loader pick-up begins to reset. After
pick-up goes to the proper position, detect switch will give a signal to MT1389, MT1389 begins to output
focus, main axis and laser signals, disc begins rotating and pick-up begins to identify disc information
and judge whether disk is CD disc or DVD disc according to disc information in order to output level from
pin IOA and control disc switch circuit and pick-up PD IC to make the corresponding action, meanwhile
Mt1389 adjusts laser output power through laser power control circuit.
After loader reads disc information, A, B, C, D, E and F signal are formed through photoelectric
conversion to MT1389 (DVD only has A, B, C, D signals) and RF signal and output from pin 2~11, 18, 19
of MT1389 respectively, after amplifying processing of pre-amplifier inside MT1389, now signals are
divided into 2 ways inside MT1389: one part, through summation amplifying and subtraction circuit inside
MT1389, produces servo error signal, after digital servo signal circuit processing, forms corresponding
servo control signals, outputs FOO, TRO, DMO and FMSO servo control signal from pin 42, 41, 37 and
38 of MT1389 respectively and then send to servo drive circuit for drive amplifying through the
integration circuit composed by resistor and capacitor and bring along focus coil, trace coil, main axis
Electric machine and feed electric machine after drive amplifying. Among these, focus and trace servo are
used to correct objective position accurately; feed servo is used to bring along laser head to make radial
large-scale move which belongs to the preliminary adjustment to laser head position; and main axis servo
is used to control main axis electric machine to make it read signals in means of constant Linear velocity
and bring along disc to rotate. After processing of amplification by VGA voltage control amplifier and
Equalization frequency compensation inside MT1389, another part of signals are changed Into digital
signals through internal A/D converter. When loader is reading CD/VCD signals, these signals are
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