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DA100 (50Hz) Chassis – Article for Television Magazine
Picture Rotation
Due to the width of a 16:9 CRT the horizontal tilt of the picture can be influence by external magnetic
fields. To overcome this problem, an extra coil is fitted around the CRT, which is connected to a DC
amplifier, controlled by the microprocessor.
fields. To overcome this problem, an extra coil is fitted around the CRT, which is connected to a DC
amplifier, controlled by the microprocessor.
Figure 58: Picture Rotation Circuit (located on CRT PWB)
Circuit Description
The microprocessor (IC1001) will output a PWM signal from pin 55. This signal is then passed through
a LPF comprising of R1620 and C1608 and fed to an error amplifier (IC1601). 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 end user has control of this adjustment via the picture menu.
Notes
a LPF comprising of R1620 and C1608 and fed to an error amplifier (IC1601). 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 end user has control of this adjustment via the picture menu.
Notes
The location of this circuit can vary between 66cm models (located on CRT base) and 76cm models
(located on sub PWB).
(located on sub PWB).
The circuit is not fitted on the HW series of televisions or the 56FW53H.
Page 60 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
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