Sony DTC-A8 / PCM-2600 / PCM-2800 Service Manual ▷ View online
— 74 —
6-4. Capstan (ATF) Servo Circuit
Fig. 6-8. Capstan (ATF) Servo Block Diagram
Fig. 6-9. Capstan Servo Waveform Timing (SP Mode)
A
B
34
26
PB RF
Q2
TP (RF)
21
20
SWA
OUT
SWITCH
AMP
EQ
IN
PCM
EQ
PB
LIMIT
PILOT
FILTER
PILOT
GCA
PILOT
ENV
1
11
RF (REC/PB) AMP
IC1 CXA1364R
14
GCA
CTL
TP (GCA)
1
LPF
IC521
3
80
PWM
CREATION
TRACKING
LEVEL DET
79
TP (SWP)
1/2 DIVIDER
IC519 SN74HC74
1/2
9
11
77
9.4MHz
MST-CLK
18.8MHz
IC503 CXD2605Q
XT10
13
A/D
CONVERTER
TRACKING
ERROR DET
PB
REC
SPEED ERROR
DET
69
CFG
PWM
CREATION
84
2
66
TP (ATF IN)
P ENV
OUT
PB RF
BUFFER
Q521
LIM
OUT
78
ATF
SYNC DET
CPRV (H:RVS)
MECHA MICON
(SERVO PROCESS)
IC502
PBDT
ATF-IN
ATF
PILOT
RFDT
IC503 CXD2605Q
RFDT
37
LPF
IC522
PWM
BUFFER
5
7
CEER
CAPSTAN
MOTOR
DRIVE
IC1, Q3
CP-DRIV
CPWM (36.7kHz)
M
M902
CAPSTAN
MOTOR
SENSOR AMP
IC3 CX20115A
10
14
16
CFGI1
CFGI2
FG
2
3
4
AGC
PWM
47
SWP
IN
A HA
IN
B HA
IN
DRUM
REC/PB
HEAD
1
SWP
— 75 —
Circuit Operations
As shown in the block diagram in
Fig. 6-8
, the FG signal (520 waves) from the capstan motor is waveform-shaped by
the sensor amplifier (IC3) and is input to Pin ^ª (CFG) of the mechanism microprocessor (servo process, IC502). Inside
the mechanism microprocessor (servo process), servo calculation is carried out with the reference clock created from this
capstan FG (CFG) and master clock (MST-CLK) and the reference clock to detect speed error. The FG signal is then
converted to a basic 36.7 kHz PWM wave and output from Pin *¢ (CPWM). Furthermore, this PWM output is the
converted to an analog signal in the LPF (IC522), and controls the rotation of the capstan motor (M902) through the
motor drive (IC1, Q3) in the next stage. This is the speed servo.
the mechanism microprocessor (servo process), servo calculation is carried out with the reference clock created from this
capstan FG (CFG) and master clock (MST-CLK) and the reference clock to detect speed error. The FG signal is then
converted to a basic 36.7 kHz PWM wave and output from Pin *¢ (CPWM). Furthermore, this PWM output is the
converted to an analog signal in the LPF (IC522), and controls the rotation of the capstan motor (M902) through the
motor drive (IC1, Q3) in the next stage. This is the speed servo.
Table 6-4. Capstan Servo During Recording and Playback
Mode
Recording
Playback
Type of Servo
Speed servo
Speed servo + ATF servo
During playback, the speed servo during recording and ATF servo operate as shown in
Table 6-4
.
Inside the RF amplifier (IC1), only the ATF pilot signal (130 kHz) from the playback RF signal is filtered. Tracking
error is then detected using the ATF sync signal obtained from the envelope (analog) signal input to Pin ^§ (ATF-IN) of
the mechanism microprocessor from Pin !¡ (P ENV OUT) and RFDT signal input to Pin &• (PBDT), and converted with
the speed error into PWM wave and output.
During playback in the LP mode, to make the relative speed of the head the same as that in the SP mode, the drum is
rotated at 2000 rpm. Consequently, in the LP mode, because the tape speed is 1/2 of the SP mode, the head runs on one
track twice at a different head running angle from that in recording and plays back.
In this case, it is controlled with the software so that the tracking error is detected only in the part from which the
maximum head playback output is obtained in one period of the DREF (Drum Reference) which serves as the reference
signal of the drum servo, and ATF servo is imposed.
In this case, when Pin 2 (CPRV) of the mechanism microprocessor is set to “L” using the capstan motor rotation
direction control output, the capstan motor is rotated in the FWD direction.
Using the GCA signal output from Pin *º (AGC PWM), the level of the ATF PILOT signal input to Pin ^§ (ATF-IN) is
detected, the gain of the PILOT GCA (Gain Control Amplifier) inside the RF amplifier (IC1) is controlled, and the level
of the pilot signal due to the difference in the recording current of the tape played back is corrected. This is called ATF
AGC. This makes use of the fact that the sum of leak signals of adjoining tracks remains constant even if tracking
deviates and the GCA in the RF amplifier is DC-controlled so that this sum meets the reference value. The capstan motor
changes its speed to use as shown in
error is then detected using the ATF sync signal obtained from the envelope (analog) signal input to Pin ^§ (ATF-IN) of
the mechanism microprocessor from Pin !¡ (P ENV OUT) and RFDT signal input to Pin &• (PBDT), and converted with
the speed error into PWM wave and output.
During playback in the LP mode, to make the relative speed of the head the same as that in the SP mode, the drum is
rotated at 2000 rpm. Consequently, in the LP mode, because the tape speed is 1/2 of the SP mode, the head runs on one
track twice at a different head running angle from that in recording and plays back.
In this case, it is controlled with the software so that the tracking error is detected only in the part from which the
maximum head playback output is obtained in one period of the DREF (Drum Reference) which serves as the reference
signal of the drum servo, and ATF servo is imposed.
In this case, when Pin 2 (CPRV) of the mechanism microprocessor is set to “L” using the capstan motor rotation
direction control output, the capstan motor is rotated in the FWD direction.
Using the GCA signal output from Pin *º (AGC PWM), the level of the ATF PILOT signal input to Pin ^§ (ATF-IN) is
detected, the gain of the PILOT GCA (Gain Control Amplifier) inside the RF amplifier (IC1) is controlled, and the level
of the pilot signal due to the difference in the recording current of the tape played back is corrected. This is called ATF
AGC. This makes use of the fact that the sum of leak signals of adjoining tracks remains constant even if tracking
deviates and the GCA in the RF amplifier is DC-controlled so that this sum meets the reference value. The capstan motor
changes its speed to use as shown in
Table 6-5
as required.
The FG of the capstan motor is 520 waves. In the case of the example of the SP mode, the speed is 77.8 rpm (See
Table
6-1.
) and therefore, the FG (CFG) output from the motor is 674 Hz as shown in the table.
In the
G16 measure mode, it is used to measure the length and position of the tape during FF/REW immediately after
cassette loading, and search running. Based on this, tape remaining amount and reel servo speed calculation are
performed. (Normally in the playback state, the measurement is carried out at the speeds corresponding to the LP or SP
mode.)
performed. (Normally in the playback state, the measurement is carried out at the speeds corresponding to the LP or SP
mode.)
— 76 —
Table 6-5. Types of Capstan Speeds (Servo Lock)
Speed (Rate)
G0.5
G1
G1.5
G3 (Both FWD/RVS directions)
G8 (Both FWD/RVS directions)
G16 (Both FWD/RVS directions)
G1
G1.5
G3 (Both FWD/RVS directions)
G8 (Both FWD/RVS directions)
G16 (Both FWD/RVS directions)
CFG (Hz)
337
674
1,011
2,022
5,392
10,784
Purpose
LP mode
SP mode
Wide track mode (Soft tape)
Cue/Review (Low)
Cue/Review (Hi)
Measure mode
— 77 —
6.5 Reel Servo Circuit
Fig. 6-10. Reel Servo Block Diagram
Circuit Operations
Fig. 6-10
Fig. 6-10
shows the block diagram of the reel servo. FG signal (24 waves) from the T and S reel sensors attached to the
reel motor (M903) is input to Pin ^¶ (TFG) and Pin ^• (SFG) of the mechanism microprocessor (servo process, IC502).
In the calculation circuit of the mechanism microprocessor, the period and period ratio are detected by the two reel FG
(TFG and SFG) signals. The optimum values of the speed and back tension at those positions are calculated from the
tape length and tape position data obtained in the measure mode. After converting the FG signals to the basic 36.7 kHz
PWM wave, they are output from Pin *¡ (TPWM) side T and from Pin *™ (SPWM) for side S.
These PWM outputs then drive the respective reel motors via the LPF (IC520) and reel drive (T side : Q512 to Q514, S
side : Q515 to Q517).
Pin (ª (XTLK) output “L” during loading and unloading using the LOCK control output of the T side reel motor and
locks the T side reel motor. As a result, the T side reel table operates during the operation and prevents the tape from
slacking.
PM901 is a brake plunger attached inside the reel motor. During modes that rotate the reel motor such as FWD and FF,
it is absorbed by the approximately 50 ms kick pulse output from Pin 4 (BPKI) of the mechanism microprocessor and
ON signal from Pin 3 (BPON) to release the brake.
(The operations of the plunger driver circuit are described in 7-4.)
In the calculation circuit of the mechanism microprocessor, the period and period ratio are detected by the two reel FG
(TFG and SFG) signals. The optimum values of the speed and back tension at those positions are calculated from the
tape length and tape position data obtained in the measure mode. After converting the FG signals to the basic 36.7 kHz
PWM wave, they are output from Pin *¡ (TPWM) side T and from Pin *™ (SPWM) for side S.
These PWM outputs then drive the respective reel motors via the LPF (IC520) and reel drive (T side : Q512 to Q514, S
side : Q515 to Q517).
Pin (ª (XTLK) output “L” during loading and unloading using the LOCK control output of the T side reel motor and
locks the T side reel motor. As a result, the T side reel table operates during the operation and prevents the tape from
slacking.
PM901 is a brake plunger attached inside the reel motor. During modes that rotate the reel motor such as FWD and FF,
it is absorbed by the approximately 50 ms kick pulse output from Pin 4 (BPKI) of the mechanism microprocessor and
ON signal from Pin 3 (BPON) to release the brake.
(The operations of the plunger driver circuit are described in 7-4.)
13
14
1/2
1/2 DIVIDER
SN74HC74
IC519
11
9
DAT DSP
CXD2605Q
IC503
9.4MHz
MST-CLK
77
67
68
81
TFG
SFG
3
TPWM (36.7kHz)
LPF
IC520
1
XTLK (L:TLOCK)
T-REEL
DRIVE
Q512-514
M
T
SIDE
XT1I
XT1O
X502
18.8MHz
ROTATION
DET
PERIOD
RATIO
DET
99
82
4
3
5
7
LPF
IC520
SPWM (36.7kHz)
BRAKE-PM
DRIVER
Q506-508,510
S-REEL
DRIVE
Q515-517
M
FG
M903
REEL MOTOR
FG
S
SIDE
BPKI
BPON
MECHA MICON (SERVO PROCESS)
IC502
19
20
5
6
EEP ROM
IC517
XROM
CK
XROM
DT
PM901
PWM
CREATION
PWM
CREATION
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