Second Power Management System Circuit - NEC MultiSync FP1370 Service Manual

8-18. Second Power Management System Circuit

When the horizontal and vertical Sync. are missing, power supply circuit to operate with IC621 becomes
"SUSPEND STATE" or "OFF STATE" condition.(Refer to item 8-10.)
Then,the voltage of "SINK" becomes low level and Q653 turn on.
The voltage of IC651 pin1 decreases low level and IC651 operation stop.
(Output +20V and -20V fall.)
When the horizontal and vertical Sync applies again, power supply circuit to operate with IC621 becomes
"ON STATE". And the voltage of "SINK" becomes high level and Q653 turn off.
At this time, IC651 operation start and output +20V and -20V rise.
SINK
3
DRAIN
CONTROL
IC651
SOURCE
2
PC651
R655
R657
1
Q653
R656
+
-
C653
(Fig.8-19) Power Management System Circuit
T651
R651
D651
+
-
C651
8-54
D6L1
+
C6L1
-
+
C6M1
-
D6M1
+20.0V
GND
-20.0V