Chapter 2—Functional Descriptions
Model 330, 340SC and 370SC Service Model 2-11
High Voltage Power Supply
The High Voltage Power Supply is a DC-DC converter (see Figures 2-6 and 2-7)
and is located on the left side of the CRT housing. It provides all necessary
voltages for the CRTs except the cathode drive, which comes from +107V from
the SPS.
Figure 2-6
High Voltage Power Supply
Input power is +24V at 5A from the SPS. The input power is converted into the
high voltage necessary to bias the CRTs.
The HVPS is controlled by an enable line (/HVEN) originating at the Video
Processor Board. This enable line is controlled by logic that turns the HVPS off
when there is a fault that could damage the CRTs. There are two (2) different
conditions that could damage the HVPS:
1.
If the +5V supply to the VPB is interrupted, the control and protection is
compromised and the HVPS must be turned off.
2.
If the cathode drive power is lost on one of the Video Amplifiers, the
cathode current cannot be controlled and the HVPS is turned off.
3.
Further details regarding this logic can be found in the functional
description on the Video Processor Board in Section 2.6.4.
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