Pioneer DEH-1350B Service Manual page 65

2) RF Amplifier and RFAGC Amplifier
The photo-detector outputs (A + C) and (B + D) are
added, amplified and equalized on this LSI and then
output to the RFI terminal as the RF signal. (The eye
pattern can be checked by this signal.)
The RFI voltage low frequency component is :
RFI = (A + B + C + D) × 3.2
RFI is used on the FOK generator circuit and RF offset
adjusting circuit.
R207 is an offset resistor for maintaining the bottom
reference voltage of the RFI signal at 1.5 VDC. The D/A
output used for the RF offset adjustment (to be
described later) is entered via this resistor.
After the RFI signal from Pin 77 is externally AC
coupled, entered to Pin 76 again, then amplified on the
RFAGC amplifier to obtain the RFO signal.
The RFAGC adjustment function (to be described later)
built-in the LSI is used for switching feedback gain of
the RFAGC amplifier so that the RFO output may go to
1.5 ± 0.3Vpp.
The RFO signal is used for the EFM, DFCT, MIRR and
RFAGC adjustment circuits.
CN101
10k
A+C
82
6
83
84
B+D
13 85
10k
C216 3pF
R204
R205
10k
10k
C217
27pF
R206
R207
1.8k
12k
RFI
66 80 79 77
D/A
10k
16k
10k
16k
Fig.3 : RFAMP, RFAGC AND FOK CIRCUIT
3) RFOK Circuit
This circuit generates the signal that is used for
indicating the timing of closing the focus or state of the
focus close currently being played. This signal is output
from Pin 4 as the FOK signal. It goes high when the
focus close and in-play.
The RFOK signal is generated by holding DC level of the
RFI at its peak with the succeeding digital section, then
comparing it at a specific threshold level. Thus, the
RFOK signal goes high even if the pit is absent. It
indicates that the focus close can take place on the disc
mirror surface, too.
This signal is also supplied to the micro computer via
the low pass filter as the FOK signal and used for the
protection and the RF amplifier gain switching.
C215 C213
0.1µF 3900pF
AGCI RFO
76 75
12k
10k
FOK
A/D
CIRCUIT
CX-958
74
TO EFM
CIRCUIT
4 FOK
3