Akai VS-2EGN

6. THE POWER /SYSCON CIRCUIT
6-1 INTRODUCTION
The power & syscon circuit consists of a power supply
circuit, and a microprocessor (syscon) and associated
circuits. (Note that the tuner and timer control section
are not included.)
For the power supply section, the timer data count, time,
etc. are displayed on the TV screen rather than using
FLD, thereby eliminating the need for a transformer for
FLD, In addition, all ICs in use operate on 4) power, eli-
minating the need for (-) power.
6-2 POWER SUPPLY SECTION
The
power
supply
circuit
consists
of
unregulated
9V
and
19V
circuits.
The
action
of
each
of
the
circuits
is
as
fol-
lows:
6-2-1 UNREGULATED 9V CIRCUIT
1) IDL5V
5V is generated from UNREGO9V by a 3-terminal regu-
lator (TA78LOOSAP). IDLSV is used both in POWER
SYSCON and on OPERATION PCB.
2) Line Frequency (LF)
fe by 07
a: Ba pa.
sv
| \ / \ | \ 50/60Hz
= Y 7 y You
ELIMINATED.
by bee
Fig. 7-100 Waveform of Line Frequency (LF)
i
i
a
Line frequency (LF), on which micro-computer power
failure detection and timing are based, is produced from
AC9V and supplied to OPERATION PCB.
6-2-2 UNREGULATED 19V CIRCUIT
1) SERVO 19V and drum heater 19V
The power is supplied to SERVO PCB as drum heater
19V and SERVO 19V. It is regulated in the servo cir-
cuit. To reduce power consumption, the power to the
UNREG 19V->@)
drum heater is turned off/on as the servo power is turn-
ed on/off, and heater current is also reduced as much
as possible.
Thus, while the servo is operating, the drum heater is
turned off, or vice versa, so as to balance the power
supply.
SERVO 19V is controlled by SERVO. The purpose is to
achieve power saving and simplicity in circuit design by
turning on/off the power to the servo system as the
drum motor is turned on/off.
2) IDL 12V
IDL 12V, which is used as the power to the booster and
remote control receiving section, is produced from UN-
REG 19V by a 3-terminal regulator IC1 (TA781012AP).
3) EE 15V
By making EE voltage available at 15V, it becomes pos-
sible to incorporate a 3-terminal regulator within the
video PCB. This eliminates the need for re-adjustment
after assembly of VRs already adjusted on the PCB prior
to assembly. (This applies only to circuitry associated
with EE12, however.)
4) AL12V and ALISV
AL15V is used for the mechanism (reel motor, loading
motor and plunger ) as well as for EE 15V, AL12V is
produced from AL15V.
On VS-2, PB12V and REC12V are produced from AL
12V.
ALI15V and AL12V are produced in IC2 (STK-5315).
STK-5315 is a hybrid IC incorporating 15V and 12V re-
gulators. (See Fig. 7-101.)
Semi-regulated AL1SV (15 + 0.3V) is used as the volt-
age for the drive circuit for each of the following mecha-
nism driving components:
@® Plunger
® Loading motor
© Reel motor
@ Lamps
The use of the semi-regulated voltage ensures that even
with AC input voltage fluctuation of 10%, stabilized
mechanism driving can be achieved if 15V REG is kept
stable, and that the proper plunger current can be ob-
tained without being affected by AC input fluctuations.
All this has resulted in reduced current for each of the
mechanism components (e.g., plunger take-in current......
0.5A with VS-2 against 2A with VS-5)
‘ALISV ALI2V
Service Manual VS-2EGN
72
Fig. 7-101 STK-5315 Equivalent Circuit