Mitsubishi Electric VS-45605 Technical Training Manual page 65

RGB Output Amps & AKB
The RGB Output Amplifier circuitry on all three
PCB-CRTs is the same, except for component no-
menclature. Only the Green Output Amplifier is
shown in Figure 7-8. The Red and Blue Amplifiers
are the same circuit configuration, except they re-
ceive their respective signal from the PCB-CRT(G),
rather than directly from the PCB-SIGNAL.
Referring to Figure 7-8, the Green video signal is
amplified by Q6G0 and Q6G2. Q6G0 is a common
base configuration, signal is input at the emitter and
output at the collector. This configuration improves
isolation between the input and output circuits.
The second stage, Q6G2, is an emitter follower, ap-
plying the Green signal to the Green CRT cathode.
The rest of the circuitry shown on the PCB-CRT(G)
is part of the AKB Circuit.
AKB Circuitry
The AKB circuitry automatically adjusts the CRTs
Cutoff Bias point if CRT characteristics change with
age. To detect a change in CRT characteristics, the
circuitry automatically checks the point at which each
CRT starts to conduct, and compares it to the previ-
ous Cutoff setting.
To determine the CRT conduction starting point, an
AKB pulse is inserted in each of the Red, Green and
Blue video signals, refer to Figure 7-9. The pulses
are inserted in the RGB Output Buffers in the VCJ.
The AKB pulses are inserted during the Vertical
Blanking Interval (VBI) of each signal, one pulse per
field. The AKB pulses are approximately the width
of one horizontal line. One pulse is generated for
each color. The three pulses occur in sequence, on
three successive horizontal lines.
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