Chapter 1. Common Circuits; Geometry Adjustment - Panasonic EURO 4 Chassis Technical Manual

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Chapter 1
1.

Geometry Adjustment

Large screen CRT's require an additional circuit which
is used for picture geometry adjustment. This
additional circuit is used to cancel the effects of the
earths magnetic field.
This circuit is provided by IC1901 [ IC1900 Euro 4D ]
(located on the
TNP8EM020) which contains two op-amps. These
op-amps being configured as push-pulls devices.
IC1901 [ IC1900 Euro 4D ] is fed a d.c. current which
can be adjusted by the user via the OSD display. Here
the user can adjust the picture geometry in 54 steps
(+26 / -27).
By increasing the OSD value the d.c. current to
IC1901 [ IC1900 Euro 4D ] is also increased, under the
control of microprocessor IC1101 pin 77, which is
used to control the current fed to IC1901 [ IC1900 Euro
4D ] pins 3 and 6.
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M-Board TNP8EM021
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Pin 3 is fed to the inverting input of internal op-amp1,
while the input via pin 6 is fed to the non-inverting input
of op-amp2.
The result of increasing this d.c. current to the
inverting input of op-amp1 is to reduce its output, while
the output of op-amp2 is amplified increasing its
or
output. This results in the picture rotating in an
anti-clockwise direction.
Likewise, when the d.c. current is decreased the
output from op-amp1 is amplified increasing its
output, while the output of op-amp2 is decreased.
This results in the picture rotating clockwise.
A cancellation coil on the AK1 series is also controlled
by IC1901, which is used to cancel any artifacts which
could corrupt the purity of the CRT.
The negative feedback loop for op-amp1 is via R1905
while the negative feedback for op-amp2 is via R1908.
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Common Circuits
AK1
Series
Only
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Cancellation
Coil
G-M
Coil
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