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3-1-6. Blanking Amplifier
Blanking signals are input from the D board, via the
B board, to the base of Q403 to switch it on. Q404
is switched off when Q403 is on, and a blanking pulse
of approximately 60 Vp-p appears at the emitter of
Q404.
The blanking pulses are then clamped at
specific DC levels and supplied to each of the three
G 1 grids of the CRT via the C board. Two individual
clamping levels can be varied by RV404 (G-BKG) and
RV40S (B-BKG), with respect to the Red channel,
for background level adjustment.
3-2.
B BOARD
The B board is an interface card for signals between
the A board and the D, H, and power supply boards.
All signal I/O, as well as DC power I/O, contain filters
to suppress RFI.
Q 1 acts as a fade control for the picture when the
monitor is powered up. When power is applied, Ql is
turned on and clamps the contrast control voltage to
a minimum.
C2 is gradually charged up and Q 1 is
switched off, returning the contrast control voltage
to the normal level.
3-3.
C BOARD
The C board relays the bias voltages and video signals
to the CRT electrodes.
Spark gaps and neon lamps
are mounted on the board to return the CRT dis-
charge (flash-over) current to chassis ground.
3-4.
D BOARD (Deflection and HV Regulation)
3-4-1. DA Board
The DA board performs the horizontal oscillator,
horizontal phase locked loop, vertical oscillator, and
vertical synchronization functions.
These functions
are processed and controlled by IC I.
The horizontal and vertical sync (HD, VD) signals
from the A board, positive true, are input to pins
CD
and
Q]
of IC 1. The H sync signal is then delayed in
phase by a PHASE SHIFTER and is input to an AFC
circuit. Meanwhile, the horizontal retrace pulse, thru
a voltage divider (C22S, C226), is fed back to pin
®
and triggers a SAW TOOTH GENERATOR.
The
delayed H sync signal and the sawtooth wave are
compared in the AFC circuit. The output from the
AFC circuit synchronizes the horizontal scanning
with the HD signal. RV20S (H-PHASE) controls the
delay time of the PHASE SHIFTER and adjusts the
horizontal position of the display image. Horizontal
deflection is driven by the output at pin
0 .
The vertical oscillator is triggered by the VD sync
signal and locked at a frequency of 60 Hz. IC 1 out-
puts two vertical rate pulses, a V drive pulse from
pin
Ii§>
and a V blanking pulse from pin
Qj) .
3-2
3-4-2. DB Board
The DB board generates waveforms, including a saw-
tooth wave, for S-correction of vertical deflection.
ICI (1/2), configured as a Miller integrator, generates
a vertical period sawtooth wave. Transistor Q 1 and
capacitor C2 control the rise and fall times of the
sawtooth wave. The bias current of the ramp genera-
tor is supplied from IC2 (2/2) to pin
@
of ICI (1/2)
and the peaks of the waveform are determined by
diodes D 1 and DS.
The resulting zero-crossing
sawtooth wave is input to the vertical deflection
circuit via RVIOI (V-SIZE) and also input to another
Miller integrator, IC2 (I/2), generates a vertical
period parabolic wave.
IC 1 (2/2) integrates the
output from IC2 (1/2) and generates an S-correc-
tion wave (similar to a sine wave) at pin
(j).
This
output is amplitude adjusted by RVI02 (V-LIN) and
is input to the vertical deflection circuit for linearity
correction. RVI03 (V-LINE BALAj\lCE) adds a DC
component to the V sawtooth wave at IC2 (1/2) to
allow adjustment of the balance of vertical linearity
at the top and bottom of the display. Additionally,
the V -sawtooth and V -sine waves are supplied to
other correction circuits on the D board.
3-4-3. DC Board
The DC board receives the horizontal retrace pulse
from T203 (HOT) and the V-sawtooth from the DB
board and generates a complex "butterfly" waveform.
Th~
sawtooth is input to Dl, 02, and D3, split into
positive and negative half waves, and the amplitudes
are varied by RV104, RVIOS, RVI06, and RVI07.
IC I
(l
/2) sums the amplitude adjusted sawtooth
waves to modulate the horizontal tamp signals for top
and bottom pincushion correction.
ICl (2/2) per-
forms a similar function for phase control by altering
the starting point of the horizontal ramp signals.
Meanwhile, the H retrace pulse is inverted by Q 1 and
triggers a phase control shifter composed of Q3 and
Q4 after passing thru Q2. The magnitude of the pulse
phase shift is varied by the output voltage from pin
(j)
of ICI (2/2) and allows individual phase adjust-
ments for both top and bottom pincushion distortion
correction. The output voltage from pin
CD
of IC 1
(1/2) is input to Miller integrator IC2 (2/2) with reset
switch QS activated by the collector of Q4. Accord-
ingly, a horizontal sawtooth signal, synchronized by
Q4, is generated and is amplitude modulated by the
sawtooth wave output from IC 1 (1/2). This signal is
inverted by IC2 (1/2) and is input to QI03.
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