Casio WK-1800 Service Manual page 10

POWER SUPPLY CIRCUIT
The power supply circuit provides various voltages as shown below.
The voltage VDD (+5 V) is provided as long as batteries or AC adaptor is set.
Other voltages are controlled by APO (Auto Power Off) signal from CPU.
The regulator IC BA9700A generates square waveform from pin 5 as PWM (Pulse Wide Modulation).
The LC filter makes stable output voltage (+5 V) for each circuit as shown above.
LC Filter
(To digital)
(To FDD)
(To LCD)
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PW/ON
NMI
CPU
APO
HD6433048SA89F
APO
PA7
LSI9
NMI
(To analog)
PW/SW