Circuit Description - Casio KL-1500 Service Manual And Parts List

CIRCUIT DESCRIPTION

Setting the batteries or AC adaptor (see figure 7)
When setting the batteries or AC adaptor, the voltage VDD2 is always applied to RAM and CPU since Q6
and IC5 are turned on.
Power on sequence (see figure 7)
When the power switch is turned on, PON signal is being H (PON = VDD2). CPU knows to turn the power
switch on, it provides H from VCON terminal to base of transistor Q4. Then both transistors Q4 and Q3 are
turned on, the voltage VDD1 is applied to all devices.
Power off sequence (see figure 7)
When the power switch is turned off, POFF signal is being H(POFF= VDD2). CPU knows to turn the power
switch off, VCON signal and base of Q4 will be L. Then both transistors Q4 and Q3 are turned off, Q3 stops
to supply the voltage VDD1.
Power down sequence (see figure 7)
If the voltage across the batteries lowers and the terminal DPW of CPU comes less than 4.5V, VCON signal
is L. Then both transistors Q4 and Q3 are turned off, Q3 stops to provide the voltage VDD1.
Print sequence (see figure 7)
When the PRINT button is pressed, TCON signal is H. Then both transistors Q2 and Q1 are turned on, the
voltage VP for printing will be 9V.
Q1
8.6V
8.8V
Fuse
8.6V
8.8V
0V
Q2
0V
0V
0V
8.4V
0V
IC5
8.6V
8.4~0V
8.8V
8.4~0V
0V
0V
+
VDD1
IC1
5.0V
4.8V
+
4.8V
0V
VCON
DPW
CPU
VDE
TCON
Note : The voltages around transistors mean as follows;
Upper figure : Power ON at no operation.
Lower figure : Power OFF.
Figure-7
— 5 —
VP (+9 V)
VDD2 (+5 V)
Q3
5.0V 4.8V VDD1 (+5 V)
4.8V 0V
4.2V
4.8V
0V
4.8V
Q4
0V
0V
GND
ON
PON
POFF
OFF
Power Switch