Drawer Motor Control; 3*3 Servo- 2 Pcp 1.769*330; Radial Control; Radial Control Circuit - Revox B225 Maintenance Instructions Manual

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B225
SECTION 3/4
3.2.2 Drawer motor control
The drawer motor amplifier
(IClOa, R 5 2 , 5 3 , 5 6 , 57, and
R 5 8 , C 1 4 , Q8 and Q9) is controlled through the shift
register IC3 (pins 4 and 5 ) . If the drawer movement
is blocked during the opening or closing operation,
the motor current rises and hence the voltage across
R 6 4 . Signal Tl of the master processor consequently
changes'to "L" (circuit R40,54,55,59,63, Q 6 , ^ Q 7 , C 1 3 ,
and I C l O b ) . In response the master processor reverses
the direction of the drawer movement.
3.3
SERVO-2 PCB 1.769.330
The SERVO 2 PCB 1.769.330 contains the circuits for
radial control and the IR receiver.
3.3.1 Radial control
A moving arm allows the laser pick-up to follow the
track horizontally. This arm basically functions like
a moving coil instrument.
The radial-control circuit can be subdivided into four
b l o c k s :
- Radial control circuit
- AGC circuit
- Offset control circuit
- Track detection circuit
3.-3.2 Radial-control circuit
The value of the radial-error signal can be computed
as follows^ RE= kd (II + 1 2 + 1 3 +14) - k (II + 1 2 ) .
The value of k is determined by the AGC circuit, and
d by the offset control circuit.
RAD-ERR2 = 1 1 + 1 2
RAD-ERR1 = 1 3 + 1 4
The signals RAD-ERR1 and RAD-ERR2 are summed via the
circuit IC9b, R58/59/61/62/63 and Q6. The sum flows as a
current through R63 and Q6. The error signal RAD-ERR 2 is
converted via R55 and R57 to a current that flows through
R54 and transistor E of IC8. The factor k is formed by
transistors A and B as well as C and D (IC8), factor d is
formed by Q5 and transistor F (IC8).
The signal RAD-ERR 2 x k (=k [II + 12]) on pin 10 of IC9c
appears on pin 9 of IC9c; the signal [RAD-ERR1 +
RAD-ERR2J kd (= kd [11 + 12 + 13 + 14j) appears on pin 10
of IC9c. The difference signal (RE), developed in IC9c,
appears on Pin 8 (RE = kd [II + 12 + 13 + 14 j - K[I1 +
K2j ) . The "lag" network of the radial control is
implemented by R66, R 6 7 , R68, C15, and IC9d, the "lead"
network by R69, R7 0, and C16. The signal is conducted to
IC5 through the protective diodes D5 and D 6 . The signal
is^taken through switch B (IC5) to pin 2 of IC2 which
together with Q 2 , Q 3 ; R 6 , R7", R 8 , R T 1 , and C5 constitutes
the_output stage for the radial-control signal RAD-MOT+/
-RAD-MOT-. RT1 protects the coil;- ThJBMwontrol can be
disabled (Signal R C - o ) . This occurs in search, p a u s e ,
forward and reverse mode. The laser pick-up can be
positioned during this phase with the signals R C - 1 , R C - 2 ,
CUR-DIR, and CUR-SUM.