3
Fig. 2 Rectifying circuit and standby power
F801 D899 C801
T801
D801
R810
C810
+5V-1
QB30
Q843
SR81
Q840
+5V (to MICOM)
Reset
C840
T840 D840
C843
C842
1
2
5
4
3
Surge
L901
Rectified
output
MICOM
POWER
THERMISTOR
2. Stand-by Power Supply
The stand-by power supply supplies 12Vdc to the re-
lay SR81, 5V to the microprocessor, 5V to the protect
IC, and a reset 5V to the microprocessor. T840 sup-
plies a low AC signal to D840. D840 rectifies the sig-
nal and C840 filters it to produce 12Vdc. The 12V is
applied to Q840. Q840 outputs a regulated 5V on pin 5
and supplies a reset 5V at pin 4. Reset occurs when
power is first applied to Q840. The 5V on pin 5 comes
up first while pin 4 stays low. This is the reset condi-
tion. After C843 fully charges, pin 4 goes to 5V for
normal operation.
3. Main Power Supply
1. Main Power Rectifier Circuit
D801 and C810, the rectifier and filter for the main
switching supply, produce 165V. R810 suppresses the
rush current at turn on. SR81 is a relay that turns on the
main supply. The relay is controlled by the micropro-
cessor through the relay drivers: QB30 and Q843.
165V DC
*
Troubleshooting Tip:
A loss of the 5 V or reset 5V will prevent the
microprocessor from operating.
*
Troubleshooting Tip:
Because the microprocessor controls the relay, the
main power supply may not turn on if the micro-
processor does not operate properly.
