Chapter 2—Functional Descriptions
2-54 Model 330. 340SC, and 370SC Service Manual
high resulting in shutdown of grid bias at the Video Amplifier Boards. Also,
the SWEEPOK status bit will be transmitted as a low to the SCB.
/GVIDOK
Similar to /RVIDOK.
/BVIDOK
Similar to /RVIDOK.
Output
/HVEN
When either /RVIDOK, /GVIDOK, or /BVIDOK from the Video Amplifier
Boards is pulled high, or the +5V power on the Video Processor Board goes
low, /HVEN is pulled high. This results in the HVPS being disabled, thus
shutting down high voltage to the CRTs.
/RENABLE
High will cause grid voltages at the VAB to be pulled low shutting off the red
CRT beam. High will result from high on /RVIDOK, /GVIDOK, or /BVIDOK
from the VAB, +5V power going down on the VPB, or /SWEEPOK being
pulled high from the VDB.
/GENABLE
Similar to /RENABLE.
/BENABLE
Similar to /RENABLE.
Internal
None
Video Amplifier Board P/N 103567 or 103774 (VAB)
The Video Amplifier Board (VAB) is mounted on and plugs into the back of the
CRT. There are three (3) VABs—one (1) on each CRT and each is entirely
dedicated to servicing its respective CRT. The video amplifier boards are the last
stage of the video chain and provide all electrical connection to the CRTs except
for anode voltage and chassis bond.
The following functions are provided by the VPB:
Connection of all voltages to CRT.
Amplification of video signal.
Blanking.
DC restore.
Bias voltage control.
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