Pioneer DEH-1350B Service Manual page 68

CX-958
10) EFM Circuit
This circuit is used for converting the RF signal to
digital signal consisting of "0" and "1". The RFO signal
from Pin 75 is externally AC coupled, entered to Pin 74,
then applied to the EFM circuit.
Loss of the RF signal due to scratches or stains on the
disc, or vertical asymmetry of the RF due to variations
in the discs manufactured can't be eliminated by AC
coupling alone. This circuit, therefore, controls the
reference voltage ASY on the EFM comparator by use
of the fact that "0" and "1" appear fifty fifty in the EFM
signal. By this arrangement, the comparate level is
constantly maintained at almost center of the RFO
signal level. The reference voltage ASY is generated
when the EFM comparator output is passed through
the low pass filter. The EFM signal is output from Pin
71. It is a 2.5 Vp-p amplitude signal centering on REFO.
C213
RFI
3900pF
6
40k
74
40k
75k 15k
Fig.9 : EFM CIRCUIT
EFM. SIG
R202
2k
10k
71
EFM
3300pF
72
R203
ASY
39k
40k
C211
0.1µF
40k
C210