Read Sharp 76FW-53H (serv.man13) Service Manual online
Colour Television – DA100/DW100 Chassis
Sharp Electronics (UK) Ltd
Technical Support
September 99
Page 13
PICTURE ROTATION
Due to the width of a 16:9 CRT the horizontal tilt of the picture can be influence by external magnetic
fields.
fields.
To overcome this problem, an extra coil is fitted around the CRT, which is connected between the
junction of Q1603/Q1604 emitter and ground.
junction of Q1603/Q1604 emitter and ground.
The microprocessor (IC1001) will output a PWM signal from pin 55. This signal is then passed
through a LPF and fed to an error amplifier (IC601). The output from this error amp can swing from a
positive to a negative voltage depending on the mark space ratio of the PWM signal from IC1001.
through a LPF and fed to an error amplifier (IC601). The output from this error amp can swing from a
positive to a negative voltage depending on the mark space ratio of the PWM signal from IC1001.
Under normal conditions (CRT is not effected by external magnetic fields) there will be no output from
the error amplifier, therefore, both Q1603 and Q1604 are turned off causing no current to flow through
the coil around the CRT neck. However if the output from the error amplifier is positive then Q1603
will turn on allowing current to flow from the +13v rail, through the coil to ground. If the error amplifier
output is negative going then Q1604 will turn on, allowing current to flow from ground to the –13v rail.
the error amplifier, therefore, both Q1603 and Q1604 are turned off causing no current to flow through
the coil around the CRT neck. However if the output from the error amplifier is positive then Q1603
will turn on allowing current to flow from the +13v rail, through the coil to ground. If the error amplifier
output is negative going then Q1604 will turn on, allowing current to flow from ground to the –13v rail.
The end user has control of this adjustment via the picture menu.
Note
The location of this circuit can vary between 66cm models (Located on CRT base) and 76cm
models (located on sub PWB).
models (located on sub PWB).
+
-
1kHz PWM
IC1001, pin 55
IC1001, pin 55
R1620
10k
10k
R1619
100k
100k
C1608
10
10
R1617
2k2
2k2
D1607
2v4
2v4
C1609
10
10
R1618
100k
100k
R1616
100k
100k
C1610
100nF
100nF
IC1601
C1611
10nF
10nF
R1615
1M
1M
R1624
100
100
R1622
470
470
Q1603
Q1604
-13v
R1623
100
100
R1621
100
100
+13v
C1613
220
220
C1612
220
220
Tilt Coils
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