Akai VS-2EGN - Page 52

(B) CUE mode
In
the
CUE
mode,
analog
switches
G,
E
,
and
A
are
ON.
The
MMS
time
constant
providing
the
basis
for
the
speed
control
is
C17
(0.002
uF)
and
R149 x (R150 + R151)
R149 +(R150+ R151)
150 kohms x 7.7 Mohms
150 kohms + 7.7 Mohms
VRI4
+ 68 kohms = 215 kohms
In the CUE mode, therefore the drum motor speed is
increased by 2.013% compared with the normal mode so
as
to
make
the
horizontal
frequency
of
the
PB
video
sig-
nal equal to the reference horizontal frequency.
©) REVIEW mode
Tn the REVIEW mode, analog switch G is ON. The MM5
time constant providing the basis for the speed control is
R148 (5.6 kohms) + R149 (150 kohms) + VR14 (68
kohms) = 223.6 kohms
In the REVIEW mode, therefore the drum motor speed
is
reduced
by
3.733%
compared
with
the
normal
mode,
thus
making
the
horizontal
frequency
of
the
PB
video
signal
equal
to
the
reference
horizontal
frequency.
3-3-4
DRUM
MOTOR
PHASE,
SERVO
CANCELLATION
CIRCUIT
COLOR
PHASE ADJ
RI9 VRB R20
SERVO
12VO0
Ait
1
:
a
,
8 Ic6 c
a McuiBce eI ee MCI4066BCP
‘cl ee a ind 17a GUE or RIVIEW/
ORUM MOTOR 1c3 V2 > |@ brum MoToR
SPEED ERROR ie, J HIGHT SPEED: ON
VOLTAGE a“ eG
"ANGSI4 Ris
3
ict
®
= ORUM MOTOR
1 SPEED CONTROL
CUE or REVIEW:L 1©
1c6 @ L@l
Ic2 MC14066 BCP
CUE or REVIEW : H
ic1 ©
ORUM MOTOR
PHASE ERROR
VOLTAGE
Fig.
7-54
Drum
motor
phase,
servo
cancellation
circuit
1) CUE or REVIEW mode
On VS-2, the Drum Motor phase servo is cancelled at
CUE or REVIEW MODE; ie., only the Drum Motor
speed servo is in use. Thus, by turning off IC2 (MC
14066BCP) Analog Switch ® , or the point where
the phase and speed systems are connected, it is possible
to prevent an error voltage in the phase system inter-
fering with the speed system. Also, the Analog Switch
circuit is incorporated in the form of color phase ad-
justment to compensate for a speed error at Quick Find-
er Mode.
2) Drum motor at abnormally high speed
In addition, the phase control system may also be can-
celled when the-drum motor rotates at an abnormally
high speed. This is done by means of a comparator
(IC3, AN6914). That is, the comparator output (IC3
pin(2)) goes to “L” at CUE/REVIEW MODE, and 4.8 V
appears at the inverse input terminal (IC3 pin @) at
“Normal” mode. When the motor revolution becomes
so high that the S/H OUT of IC1 (AN6350 pin(8)) falls
below 4.8 V, the comparator goes to “L”, and the phase
system is cancelled, thereby eliminating interference to
the phase system and preventing “hunting” of the drum
motor.
Note: Normal Mode ~ Recording Mode or Normal
Playback Mode.
————
Service
Manta
VS-2EGN
49