Pioneer DEH-1350B, Service Manual

Page: 67 / 82

CX-958
7) DFCT (Defect) Circuit
The DFCT signal is used for detecting defects on the
mirrored disc surface. It allows monitoring from the
HOLD pin (Pin 2). It goes high when defects are found
on the mirrored surface.
The DFCT signal is generated by comparing the RF
amplified signal (which is obtained by bottom holding
the RFO signal) at a specific threshold level by the
succeeding digital section.
Stains or scratches on the disc can constitute the
defects on the mirrored disc surface. Thus, as long as
the DFCT signal remains high in the LSI, the focus and
tracking servo drives are held in the current state so
that a better defect prevention may be ensured.
8) 3TOUT Circuit
The 3TOUT signal is generated by entering disturbance
to the focus servo loop, comparing phase of
fluctuations of the RF signal 3T component against that
of the FE signal at that time, then converting the signal
to DC level. This signal is used for adjusting bias of the
FE signal (to be described later). This signal is not
output from the LSI, thus its monitoring is not available.
9) MIRR (Mirror) Circuit
The MIRR signal shows the on track and off track data,
and is output from Pin 3.
When the laser beam is
On track : MIRR
=
"L"
Off track : MIRR
=
"H"
This signal is used on the brake circuit (to be described
later) and also as the trigger to turn on track counting
when jumping take place.
The MIRR signal is supplied to the micro computer, too,
for the protection purpose.
A/D
MIRR
CIRCUIT
3T
CIRCUIT
DFCT
CIRCUIT
BOTTOM DETECT
BOTTOM DETECT
PEAK DETECT
LPF S/H
A/D
A/D
76
75
73
3
2
40k
20k
20k
40k
40k
40k
200k
200k
C212
0.1
µ
F
C3T
AGCI
RFO
12k
10k
20k
30k
MIRR
HOLD
Fig.6 : DFCT, MIRR AND 3T DETECTION CIRCUIT
Fig.7 : HOLD OUTPUT WAVEFORM
(When surface defects are present)
Fig.8 : MIRR OUTPUT WAVEFORM
(When an access is made)
5
Surface defects
RFI
HOLD
RFI
MIRR
OFF Track ON Track