Circuit Explanations; Power Supply Circuit - Casio PCR-255 Service Manual

6. CIRCUIT EXPLANATIONS

6-1. Power supply circuit

T1
TE-266-E2U
E412181*1
CN8
*B, *D, *G
1. Plug the power cord into AC outlet, secondary voltage (9.65VAC) of the power transformer T1 will
be appears at "A" point.
2. Then, its AC voltage is rectified by the diode bridge and change it to DC voltage. ("B" point)
3. DC voltage appears more than 7V at the corrector of power transistor 2SD2396, and then the power
transistor is turned on.
Then VP is supplied. ("C" point)
4. When the VP voltage becomes more than 3.3V, the transistor 2SD945 is turned on and then PWD
signal becomes GND level. ("F" point)
When the PWD signal becomes GND level, CPU knows no power failure.
5. VP is supplied at the DC DC converter trans T2, the DC DC converter makes display and logic circuit
voltage.
VN ,VF1,VF2 : Display voltage ("I", "J" point )
VDD
Transistor 2SD1803 is used for oscillating the primary voltage of DC DC converter trans.
A
1SR35-100A X 4
6
D1
D2
D3
D4
F1
10
FUSE 1A
B
: Logic circuit voltage ("H" point)
G
T2
DCS-267
1
2
R5
100
7
C5
Q2
HE12TKYB
103K
2SD1803(T)
D6 ZD3
1S2075K RD24EB2
R3
WITH HEATSINK
CRH100-FH11J-1R0
C
OSH-1625-MP
Q1 2SD2396(K)
ZD5 VDD
RD3. 3EB2
R14
470K
Q7
C23
2SC945
ECQ-B1H103-KF
C9
HE60TKYB222K
D E
— 4 —
3
VF1
4
ZD4
5
VF2
RD4. 3EB2
D7
1S2471
VN
50V4. 7uF
I
C11
8
C17
10V100µ HE12TKYB103K
C4
D5
9
VDD
1S2075K
H
VDW
VP
C28
DSTC50TKYR103K
PWD
GND
GNDP
F