Daewoo DTK-28 Series, Руководство по обслуживанию, Страница: 53 / 71

CP-850/F Service Manual
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a) Cr Cb input of CTI
b) Cr Cb input + correction signal
c) sharpened and limited Cr Cb
5.3.2.10 Analog Back End
The digital RGB signals are converted to analogue RGB by three 10-bit digital to analogue converters (DAC). Each
RGB signal has two additional DACs with 9-bit resolution to adjust analogue brightness (40% of the full RGB range)
and cutoff / black level (60% of the full RGB range). An additional fixed current is applied for the blanking level.
The back-end supports the insertion of two external analogue component signals, only one is used for OSD/Text from
the microcontroller. These signals are clamped, processed in an analogue matrix (RGB2), converted by a
voltage/current converter (VCC), and inserted into the main RGB by the fast blank switch. The analogue RGB outputs
are current outputs with current- sink characteristics.
5.3.2.11 Analog RGB Insertion
Each component signal is clamped, converted to RGB if required, and inserted into the main RGB by the fast blank
switch. The external component signals are adjustable independently as regards DC level (brightness) and magnitude
(contrast). Fast Blank selection logic Over-/underlay of the external component signal and the main RGB signal
depends on the fast blank input signal.
5.3.2.12 CRT Measurement and Control
In order to define accurate colour on different CRT displays, the cut-off and white drive settings are adjusted in factory
depending on the characteristic of CRT phosphor.To guarantee correct colours during the lifetime of the display, a build
in automatic tube control loop measures and adjusts the black level on every field and white point every third field. The
display processor is equipped with an 9/12-bit PDM-ADC for all picture tube measuring purposes. This MADC is
connected to the SENSE input pin, the input range is 0 to 2.6 V. Cutoff and white drive current measurement are carried
out with 8-bit resolution during the vertical blanking interval. The current range for cutoff measurement is set by
connecting the sense resistor RC591 to the SENSE input. Due to the fact of a 1:10 relation between cutoff and white
drive current the range select 2 output (RSW2) becomes active for the white drive measurement and connects R533 in
parallel to RC591, thus determining the correct current range. During the active picture, the MADC is used for the
average beam current limiter with a 12-bit resolution. Again a different measurement range is selected with active range
select 1&2 outputs (RSW1&RSW2) connecting R534 in parallel to R533 and RC591. These measurements are typically
done at the summation point of the picture tube cathode currents.