Read Sharp 32JW-73H (serv.man2) Service Manual online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 7
Horizontal Output Stage
The horizontal output stage employed in the GA20 chassis is a conventional transformer driver circuit
with a diode modulator for the purpose of east west correction.
If the horizontal output stage develops a short circuit, the power supply will operate in burst mode. To
confirm that it is the horizontal output stage causing burst mode operation; remove the HT feed to
T602 by disconnecting R606.
Q601
R602
220R
220R
R601
150R
150R
Q1006
T601
R605
5K6
R604
2K7
R607
15R
Q602
R606
3R3
D602
D603
C605
4700pF
C610
8500pF
C611
0.033µF
C608
8100pF
Scan Coils
East/West
C606
150pF
Part of T602
Fly-back TX
C602
560pF
150V
C601
1000pF
IC1001 Pin 76
H-drive
IC1001 Pin 81
H-mµte
4
1
H
ORIZONTAL
D
RIVE
M
UTE
Q1006 is the horizontal drive muting transistor which is controlled by the microprocessor (IC1001) pin
81, At switch on IC1001 pin 81 is high, keeping Q1006 turned on, shorting the horizontal drive to
ground. Once IC1001 start-up sequence is complete and it is ready to allow the horizontal stage to
start, pin 81 will go low turning off Q1006, allowing the horizontal drive to reach the driver transistor
Q601.
If at any time the microprocessor detects a fault where it needs to stop the horizontal drive for safety
reasons then Q1006 will be turned on again.
H
ORIZONTAL
O
UTPUT
T
HEORY
Consider the circuit at rest, i.e. the beam spot at the centre and no current flowing through the scan
coils. The S-correction (DC blocking) and the fly back tuning capacitor charged.
coils. The S-correction (DC blocking) and the fly back tuning capacitor charged.
Scan Coils
S-Correction
Fly-Back Tuning
Capacitor
Efficiency
Diode
Horizontal
Output
Direction Of Scan
Scan is initiated when the horizontal output transistor is switched on.
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