Pioneer YPM-MG2196ZF Service Manual page 64

YPM-MG2196ZF
5) Auto gain control (AGC)
AGC adjustment is already used in the CD modules of
the previous generation. This function automatically
adjusts servo loop gain of focus and tracking.
Adjustment is made in the following steps:
(1)Disturbance is input to servo loop.
(2)The system extracts error signals (FE and TE) upon
input of disturbance via the B.P.F. and obtains signals
of G1 and G2.
(3)The microcomputer reads G1 and G2 signals via the
servo LSI.
(4)The microcomputer calculates required amount of
correction to adjust loop gain in the servo LSI.
The system repeats the same adjustment process
several times to improve adjustment precision.
6) Initial adjustment value
For all automatic adjustments, the system uses the pre-
vious adjustment value as initial values, except when
the power of the microcomputer has been turned to
OFF (backup is turned to OFF). If backup has been
turned to OFF, the system uses initial set value to per-
form automatic adjustment.
7) Display of coefficients of adjustment results
Results of automatic adjustments can be displayed in
Test mode for confirmation. Display of coefficients in
each automatic adjustment is as follows:
(1)FZD cancel, TE.OFST cancel, T.BAL, and FE bias
Reference = 32 (32: No adjustment was required)
Display is made in units of approximately 40 mV.
Example: Coefficient of FZD cancel = 35
35 - 32 = 3
Corrected amount is approximately +120 mV.
Thus, FE offset before adjustment is -120 mV.
(2)Adjustment of F and T gain
Reference: Focus = 20, tracking = 20
The amount of reduced gain in comparison with the
reference is known by looking at the coefficient dis
played.
Example: AGC coefficient = 40
Amount of reduced gain = 20 log (20/40) = -6dB
64
3 x 40 mV = 120 mV
4 Power Supply and Mechanism
Control
The power supply VM (7.5V) is produced from the
power supply VD (9.0V) supplied from the Commander ,
and used as the power supply for the loading motor
driver, elevation motor driver, cam gear motor driver,
and 5V Reg IC. As for the drive voltage for the disc
detection LEDs and the power supply for the CD driver
ICs, the power supply VD (9.0V) is used.
The system IC controls the ON/OFF operations of the
CD driver and laser diodes,the 5V power supply, and
the drive voltage PVD for detection LEDs with "CONT",
"POWER", and "LOAD" signals respectively.