Read Sharp 32JF-74H (serv.man2) Service Manual online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 5
S
TANDBY
During standby Q754 is turned on by the microprocessor which has the effect of connecting D757 and
D712 in parallel across D758. This will keep the opto-coupler (IC702) turned on, simulating an over
voltage condition. IC701 is now operating in burst mode.
D712 in parallel across D758. This will keep the opto-coupler (IC702) turned on, simulating an over
voltage condition. IC701 is now operating in burst mode.
S
ECONDARY
P
ROTECTION
In the event that a secondary supply rails fails due to excessive current or increases beyond safe
limits then this power supply is designed to return to the burst start-up mode.
limits then this power supply is designed to return to the burst start-up mode.
Q704
D712
Q701
R717
10K
R719
10K
D706
R723
2K2
R707
150K
R703
150K
D710
C15
R725
2K7
D708
R724
10R
+350v
IC701 Pin 4
(demag)
1
2
Part
of
T703
IC702
IC701 Pin 1
(vcc)
IC701 Pin 3
(ctl)
IC703
C714
22µF
C705
22µF
This is achieved by a supply rail monitoring circuit which consisting of Q751, Q752, Q753, Q762 and
Q759, and a control circuit consisting of IC703, Q701, D706 and D712.
The opto-coupler (IC703) is normally turned off. If it is turns on, then thyristor D706 will conduct,
turning on Q701. Q701 emitter is connected to power supply ground and its collector is connected via
D712 to IC701 pin 1 (VCC ). Therefore, while Q701 is turned on it is impossible for the voltage at
IC701 pin 1 (VCC) to reach its turn on threshold, hence the power supply remains in burst mode.
Click on the first or last page to see other 32JF-74H (serv.man2) service manuals if exist.