Pioneer CDX-MG6056ZH Service Manual page 68

CX-890
2) RF amplifier and RF AGC amplifier
Photodetector outputs (A+C) and (B+D) are added,
amplified and equalized in IC101, and output to the RFI
terminal as RF signal. (Eye pattern can be checked at
this terminal.)
Low-frequency components of voltage RFI is:
RFI = ((A + C) + (B + D)) x 3.22
where R111 is offset resistor to keep RFI signal within
the output range of the preamplifier. RFI signal is goes
under AC coupling, and is input to Pin 4 (RFIN termi-
nal).
IC101 contains an RF AGC circuit. RFO output from Pin
2 is maintained to a constant level (1.2 ±0.2 Vp-p). The
RFO signal is used in the EFM, DFCT, and MIRR circuits.
3) EFM circuit
The EFM circuit converts RF signal into digital signals of
"0" and "1". RFO signal after AC coupling is input to Pin
1, and supplied to the EFM circuit.
Asymmetry caused during manufacturing of discs can-
not be eliminated solely by AC coupling. Therefore, the
system controls the reference voltage ASY of the EFM
comparator by using the fact that probability to gener-
ate "0" and "1" is 50% in EFM signal. This reference volt-
age ASY is generated by output from the EFM com-
parator through L.P.F. EFM signal is output from Pin 35.
As signal level, amplification is 2.5 Vp-p around
REFOUT.
REFOUT (+2.5V)
+5V
R111
27kΩ
20kΩ
CN101
10kΩ
10
6
A+C
10kΩ
11
20kΩ
10kΩ
B+D
13 13
10kΩ
12
4
R125
0R0
C105
24pF
C107
C122
R105 R104
4.7µF/35V
0.1µF
6.8kΩ 8.2kΩ
C125 5pF
6 5 4
RFI RFIN
DETECT
20kΩ
9.3kΩ
(RF AGC)
9.3kΩ
RF
ENVELOPE
HPF
VDC
Fig. 3 RF AMP, RF AGC, EFM, DFCT, RFOK Circuit
4) DFCT (defect) circuit
DFCT signal detects mirror defect in discs, and is output
from Pin 33. The system outputs "H" when a mirror
defect is detected.
If disc is soiled, the system determines it as lack of mir-
ror. Therefore, the system inputs the DFCT signal out-
put to the HOLD terminal of servo LSI. Focus and track-
ing servo drives change to Hold status only when DFCT
output is in "H" so that performance of the system upon
detection of defect can be improved.
5) RFOK circuit
The RFOK circuit outputs signal to show the timing of
focus closing servo, as well as the status of focus clos-
ing during playback. The signal is output from Pin 32.
The system inputs the RFOK signal output to the RFOK
terminal of servo LSI. The servo LSI issues Focus Close
command. The system outputs signal in "H" during
focus closing and playback.
C106
2200pF
UPC2572GS
3 2 1
Vcc
20kΩ
AGC
DEFECT
PEAK
32
RFOK
RFO
EFM
35
R107 8.2kΩ
C111 3300pF
R106 18kΩ
ASY
×12
36
C110
0.1µF
DEFECT
33 HOLD
34
C112 0.047µF
BOTTOM