Chapter 2---System Description
CRT interface for Focus, heater voltages and ARC ground
The three CRT sockets are part of the VAB. They provide the
necessary interface for the input of the three CRTs. The Focus
voltage for each color is connected directly to the socket of each
CRT.
The VAB provides ARC grounds for each CRT which are used to
protect against arcing of the CRT anode supply.
IIC Interface
The VAB does not use the IIC interface. All adjustments are
accomplished by the control lines coming from the Video
Processor Board.
The Video Amplifier Board I/O
This section provides a description of the inputs to and outputs
from the VAB. The I/O descriptions are arranged by the
source/destination of the signal. The assembly communicated with
is used as the primary heading of each group of signals. Those
signals are subdivided into inputs and outputs. Input refers to an
Input to the VAB, output refers to an output from the VAB.
Table 2-10.
Video Amplifier I/O signals
VIDEO PROCESSOR BOARD
INPUTS DESCRIPTION
RED_VIDEO
GRN_VIDEO
BLU_VIDEO
Video preamp signals. About 0.5 VPP
G1_BIAS
Brightness control line. 0 to 5 V DC
RED_G2
GRN_G2
BLU_G2
Black level (G2) control lines 0 to 3.1 V
RESTORE
Video DC restoration pulse. logic HC positive going 4% duty cycle
OUTPUTS DESCRIPTION
/VA_OK
VAB status line. Low = good VAB. High = Bad VAB (This signal is
called /HV_ENABLE at the HVPS).
RED_BEAM
GRN_BEAM
BLU_BEAM
Cathode beam current lines. about 1 volt per 100 UA
HIGH VOLTAGE POWER SUPPLY
2-30
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