Read Sharp 28JW-73H (serv.man2) Service Manual online
50Hz Widescreen
Colour Television
GA20 Chassis
Technical File
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Contents
Switch Mode Power Supply.................................................................................................................. 1
SMPS control IC ............................................................................................................................... 1
Features ........................................................................................................................................ 1
Supply (Pin 1) ............................................................................................................................ 2
Drain (Pin 8................................................................................................................................ 2
Control (Pin 3) ........................................................................................................................... 3
Burst Standby mode............................................................................................................... 3
Hiccup Mode .......................................................................................................................... 3
Demagnetization (Pin 4) ............................................................................................................ 3
Overvoltage............................................................................................................................ 3
Overpower ............................................................................................................................. 3
Current Sense (Pin 5) ................................................................................................................ 3
Short Winding Protection........................................................................................................ 3
Overcurrent ............................................................................................................................ 4
Soft Start ................................................................................................................................ 4
Drive (Pin 6)............................................................................................................................... 4
HT Regulation................................................................................................................................... 4
Standby ............................................................................................................................................ 4
Standby ............................................................................................................................................ 5
Secondary Protection........................................................................................................................ 5
Excessive EHT.............................................................................................................................. 6
CRT Heater Voltage ...................................................................................................................... 6
Horizontal Output Stage ....................................................................................................................... 7
Horizontal Drive Mute ....................................................................................................................... 7
Horizontal Output Theory.................................................................................................................. 7
Vertical Driver..................................................................................................................................... 10
Audio Output ...................................................................................................................................... 12
LOW PASS FILTER........................................................................................................................ 12
Protection ....................................................................................................................................... 13
Mute................................................................................................................................................ 14
Power On .................................................................................................................................... 14
Power Off .................................................................................................................................... 14
Off-Mute1................................................................................................................................. 14
Off-Mute 2................................................................................................................................ 14
Off-Mute 3................................................................................................................................ 14
Microprocessor................................................................................................................................... 15
Supplies.......................................................................................................................................... 15
Reset/Watchdog Circuit .................................................................................................................. 16
I
2
C Bus............................................................................................................................................ 16
Vertical Protection........................................................................................................................... 16
Safety ............................................................................................................................................. 16
LED’s .............................................................................................................................................. 17
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 1
Switch Mode Power Supply
This SMPS consists of a chopper device Q702, Power Factor Correction (PFC) Q703, SMPS
controller IC IC701, current sense R715 and soft start R713 & C706
Q702
R708
27R
R715
0R12
0R12
R713
33K
C706
0.047µf
R711
1K
C704
1000pf
C710
8200pf
C709
470pf
D705
Q703
C718
470pf
470pf
R722
47K
R720
10K
D707 C712
470pf
C713
0.033µf
R721
1K
C717
470pf
470pf
IC701 Pin 6
(Drive)
IC701 Pin 5
(I
sense
)
IC701 Pin 8
(Drain)
4
7
5
9
+ve
T703
Primary
Winding
SMPS
CONTROL
IC
Features
Universal mains supply operation (70 to 276 V AC)
Low external component count (High level of integration).
Valley/zero voltage switching for minimum switching losses
Efficient quasi-resonant operation at high power levels
Frequency reduction at low power standby for improved system efficiency (<3 W)
Burst mode operation for very low standby levels (<1 W)
Internal start-up current source.
Safe restart mode for system fault conditions
Continuous mode protection by means of demagnetization detection (zero switch-on current)
Accurate and adjustable overvoltage protection
Short winding protection
Undervoltage protection (foldback during overload)
Overtemperature protection
Low and adjustable overcurrent protection trip level
Soft (re)start
Mains voltage-dependent operation-enabling level.
Universal mains supply operation (70 to 276 V AC)
Low external component count (High level of integration).
Valley/zero voltage switching for minimum switching losses
Efficient quasi-resonant operation at high power levels
Frequency reduction at low power standby for improved system efficiency (<3 W)
Burst mode operation for very low standby levels (<1 W)
Internal start-up current source.
Safe restart mode for system fault conditions
Continuous mode protection by means of demagnetization detection (zero switch-on current)
Accurate and adjustable overvoltage protection
Short winding protection
Undervoltage protection (foldback during overload)
Overtemperature protection
Low and adjustable overcurrent protection trip level
Soft (re)start
Mains voltage-dependent operation-enabling level.