Akai VS-2EGN - Page 51

During CUE or REVIEW modes, the tape is driven
or reversed at a high speed. At this time, the relative
speed between the video head and the tape changes, and
the PB video signal horizontal frequency changes, which
means that the TV horizontal synchronization becomes
abnormal. Therefore the drum speed is changed to com-
pensate for this.
1) PAL (SECAM) mode (Refer to Fig. 7-52)
Normal mode
In normal mode, the analog switches F and E becomes
ON, and the time constant of MMS becomes C17 (0.022
MF) and R22 (200 kohms) + VR6 (68 kohms) = 268
kohms. This determines the speed control performance.
The phase Error signal is connected via the analog switch
F, and the speed control is performed by varying the
time constant of MMS, which is the basis of the speed
control.
® CUE mode
In the CUE mode, analog switches G, E and A are ON,
and F is OFF.
The time constant of MMS, which is the basis of the
speed control, is C17 (0.022 uF) and
This is 2.17% smaller than that during the Normal mode.
That is, in the CUE mode, the drum motor speed is in-
creased by 2.17% compared with the Normal mode,
thus equating the horizontal frequency of PB video sig-
nal to the stnadard horizontal frequency.
When the drum motor speed varies due to, say, toler-
ances of components, a TV picture colour offset pheno-
menon occurs. WRS5 is a colour phase adjustment con-
trol potentiometer.
© REVIEW mode
In the REVIEW mode, the analog switch G is ON. The
time constant of MMS providing the basis for the speed
control is C17 (0.0022 wF) and R15 (7.5 kohms) + R22
(200 kohms) + VR6 (68 kohms) = 275.5 kohms. This is
3.75% larger than in the normal mode. That is, in the
REVIEW mode, the drum motor speed is reduced by
3.75% compared with the normal mode, thereby making
the horizontal frequency of PB video signal equal to the
reference horizontal frequency.
R22x(R23+R24)
R224(R23#R24) * VRO
200 kohms x 9 Mohms
= 300 kohms #9 Mohims ~ 15-6 kohms
2) NTSC mode
SERVO I2V
5 COLOR
E& PHASE ADJ
RI, 100K oF une aioe
Ich
PHASE ERROR ©
CUE
or
REVIEW
LOW-—~—=——~
CUE or REVIEW HIGH-—~———————~4
al SERVO !2 Vv.
1
1
1
Ic
speed contro. ©
MM
ci7,
0.022]
RI48 5.6K
{
:.
Rigg 150K ~~”
cis
220/10] cio 47/16
SERVO I2V
RISI2.2M VRI4 68kB
DRUM MOTOR
SPEED ADJ
ICIS 1/4
Fig. 7-53 Drum Motor Speed Adjustment Circuit (NTSC mode)
Normal mode
In the Normal mode, analog switches F and E are ON.
The time constant of MMS providing basis for the speed
control is C17 (0.002 uF) and R149 (150 kohms) + VR
14 (68 kohms) = 218 kohms.
48
Service Manual VS-2EGN
The phase error signal is connected via the analog swit-
ch F, and the speed control is performed by varying
the MMS time constant which is the basis of the speed
control.