Technics SL-P222A - Page 42

SL-P222A
3-1-7 Start-up procedure
The whole start-up procedure is
sequenced by the voltage across
Capacitor C2513. Capacitor C2513 is
charged by an internal current source
of 1 pA nom.
Together with a starting capacitor
270s nF, a starting-up time
approximately 0.3 sec. is reached.
of
of
The start-up procedure is divided in
stages. The procedure is started by
putting a logical low level at the
Si/RD input.
Vsc START UP DIAGRAM
5
4
3
2
1
V(Vj)
ISTAGE 1l STAGE 2 STAGE 3 STAGE
| t(sec)
'®
| | @® +100uA + i1 +12 +13 + i4
| ® —100uA 411 + 12 +13 + 14
Cunceak © focus unit is in focus
at output
FE 0
Laser turns on and the objective is
moved to the center of the disc. The
turntable motor is switched on. The FE
pin delivers a positive going starting
current of 100 uA + the sum current (I1
+ I2 + 13 + T4).
Note the I.f. a.g.c. does not’ see
light, so max amplification.
The starting current is_ reversed,
gradually causing the -objective to go
down.
This
process
is
stopped
when
the
starting current equals the amplified
sum current (11 + I2 + 13 + I4).
Note: I1 + I2 + 13 + I4 = 100pA
4
—
— 52 —
A smooth transition is made from the
amplified sum current (I1 + I2 + 13 +
I4) to the normalized focus error
signal
I1 - I2 T4 - 13
T1+ 12° Th +13
The spot is now almost focused on the
reflective layer of the disc.
The signals to the FE pin.
STAGE 1 (starting-up current + I1 + I2
+ 13 + T4)
STAGE 2 (starting-up current + I1 + I2
+ 13 + I4)
I1 - I2 T4 - 13
Stage 3 3710 ths B
This should be almost 0
The signal to the FE lag pin.
(I1 + T4) - (13 + 12) + the
normalized FE (like in stage
3)
The arm is kept at the inside recess by
means of a binary word from _ the
microprocessor at BO, B1, B2, and B3 of
the radial error processor.