Read Sharp 28JW-74H (serv.man2) Service Manual online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 13
P
ROTECTION
This CTV is design to switch to standby is fault is detected within the audio output stages. This is
achieved by removing the voltage from IC1001 pin 63, normally IC1001 pin 63 is tied to the +5stby
supply via R1033 and L1006. An averaging circuit comprising of C1323, R1310 and R1311 is used to
sample the audio signal at the loudspeakers. Under normal conditions this average will equal zero
volts. However, with a fault condition the average will move in either a positive or negative direction.
This is detected by Q1302, Q1303 and Q1304.
Q1301
D1301
Q1303
Q1302
R1312
4k7
C1323
1µF
R1311
10k
R1310
10k
R1313
100k
R1312
100k
5v
Standby
-16v
Left
Right
If the average moves in a positive direction then Q1304 turns on removing the voltage from IC1001
pin 63, and for a average which moves in a negative direction then Q1302 and Q1303 turns on,
removing the voltage from IC1001 pin 63.
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