Panasonic EURO 4 Chassis, Technical Manual

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17.9. CRT Measurement and Control
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Finally the analogue backend is also equipped with
A/D converter which is used to perform Tube and
Picture measurement, this information being fed
from the Y-Board via transistors
Q351 , Q352 and
Q353 to the sense input pin 28 of the VDP IC601 .
The reference voltage for the measurement A/D
converter being input via pin 40 also of the VDP
IC601 .
17.9.1.Tube Measurement
Tube measurement is carried out during vertical
flyback, during this period two sets of measurements
are gated back to the VDP
IC601 pin 28.
The two sets of measurements taken during tube
measurement being cut-off for the RGB systems
and white drive for either of the R, G or B which are
carried out sequentially.
The input range of the A/D converter is set between
0 - 1.5V which has to be switched to ensure that its
input range is not exceeded. The input range of the
A/D converter is dependant upon the measurement
being taken and is controlled by pins 26 and 27 of
the VDP
IC601 .
During cut-off measurement the input range of the
measuring A/D converter is set by resistor R658.
However as the white drive measurement contains
alarger current range, resistor R607 has also to be
switched into the measurement A/D converter input
as well as R658 thus keeping the measured value in
the range of the A/D converter.
This information then passes via the I
2
C bus to the
microprocessor IC1101 which evaluates this data
and compares the data set in the memory (during
alignment adjustment) to continuously match the
measured data.
These correction values again pass via the I
2
C bus
to the fast processor in the VDP IC601 . Here the
RGB output stages are corrected according to the
values supplied, thus compensating for CRT and
component aging.
17.9.2.Picture Measurement
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