SERVICING
3828VD0171G
3-7
DIGITAL FCS - SERVICING
In the output stage the nominal input
signal will be amplified to provide a
4.6V output color signal
At maximum contrast and maximum gain
settings. Reference or pedestal black
levels are adjusted by output clamping
(pin 11 HFB).
In order to achieve fast rise and fall
times of the output signals with mini-
mum crosstalk between Channels, each
signal stage has its own supply volt-
age pin.
The pin LIM (pin 24) is a linear con-
trast control pin, which allows sub
contrast setting, contrast modulation
and beam current limiting. The maximum
contrast is defined by the actual I2C
bus setting. Input signals at pin LIM
act on video and OSD signals and do not
affect the contrast bit resolution.
ABL processing occurs inside of IC pre-
amplifier. The open circuit voltage of
the Beam Current Limiting is approxi-
mately 5V, contrast reduction starts
at input voltages <4.4V and signal am-
plification will be reduced with de-
scending input voltages.
The RGB output signals of this IC goes
directly coupled to the input pins each
power amplifier IC. Pin 2 of IC5121,
IC5141 and IC 5161.
The core of the Red amplifier is IC5121.
This IC is an operational amplifier,
configured as an inverting amplifier.
The inverting input is on pin 2 and the
non-inverting input is on pin 4. The
Feedback resistor is R5125. The ampli-
fier has a gain peaking network be-
tween pin 1 and pin 3. This network is
internally connected to the collectors
of the differential input transistors.
The input signal is connected to the
inverting input of the amplifier through
resistor R5151 to avoid Hi frequency
oscillations. The non-inverting input
is connected to a voltage bias formed
by resistors R5101and R5102. The C5122
is for AC decoupling and CM5123 is for
Hi Frequency filter purposes (one for
each IC). The IC takes this voltage
bias as a reference voltage for the
input signal. The reference voltage is
the same for the three-color amplifi-
ers. The output is at pin 12 of the IC
and goes to the CRT cathode through the
resistors R5127, R5128, for arcing pro-
tection, and the coil L5121 for peak-
ing improvement.
