Pioneer CDX-M12 Service Manual page 60

CDpx-MI12
Shown inFig. 33, 34 are a block diagram of the tracking
carriage servo system and a flow of signals in IC
UPD6374AGH. To make a track jump either forward or
reverse, tracking kick and brake voltages and carriage
kick and brake voltages are set in related registers be-
forehand. A jump forward or reverse is made at the volt-
age which has been set in an instruction from the micro-
computer.
a) Traking equalizer
in the present system, a digital filter is built in IC
UPD6374AGH, allowing a specific equalizer curve to be,
obtained according to the coefficient sent from the
microcomputer. And a passive filter is externally
mounted. These two filters are used to obtain a speci-
fied equalizer curve. To allow a stable pull-in throughout
(dB) (deg)
30
TRKG EQ
20
-20
-30
10
the search, moreover, the equalizer curve applied is so
set as to obtain a higher level of gain than that during
the play.
Fig. 35 shows the tracking equalizer curves observed
during both play and search.
TEY —» TIN
GAIN UP
(IN SEARCH
Tracking equalizer (Example)
b) Brake Circuit (Fig. 36) '
Since the actuator is put into a non-linear status in the
in-focus mode or in the track-jump mode, the pull in the
servo loop turns out very poor after completion of a
jump. While both pickup and disc are relatively moving,
the brake circuit permits tracking to be closed smoothly.
The direction in which both pickup and disc are moving
is detected, based on a phase relation between MIRR
76
Fig. 35
and tracking error signals. With an accelerating compo-
nent only cut off the tracking error, the decelerating
component only is used while repeating the ON/OFF
operations of servo on a chopper basis.
Thus, a stable pull in the servo loop is performed.
This circuit's ON/OFF operations are controlled by the
microcomputer.