Repair manual

2-68
THEORY OF OPERATION
beam does not move straight up; it moves from side-to-side during its
upward swing. This is caused by the horizontal lines being traced out
during vertical retrace.
b. Controls
Refer to paragraph 1 in this Section of the Service Manual for a functional
description of the vertical controls (CENTER and HEIGHT) that are used
to properly size and align (vertically) the CRT video display.
Refer to the Calibration and Adjustment Section in this Service Manual
for a detailed description on how the vertical controls are used in
conjunction with the provided Digital Palette Test Software (Test
Diskette) to properly size and align (vertically) the CRT video display.
8. Luminance
The Luminance (Brightness) circuit drives grid 1 of the CRT. It maintains the
CRT beam at its adjusted brightness.
This circuit, in conjunction with the COARSE and FINE LUMA (brightness)
controls (R46 and R47), adjust the brightness of the beam by changing the bias on
grid 1 of the CRT. A more negative bias decreases electron flow, turning down
the brightness. These controls are used during initial setup of the Digital Palette
to properly adjust the CRT beam to its specified brightness. Refer to the
Calibration and Adjustment Section in this Service Manual for a detailed
description on how the luminance controls are used to setup the brightness of the
CRT beam.
Once the COARSE and FINE LUMA controls are properly used to adjust the
CRT beam to its specified brightness, the auto luminance circuit and the micro
processor control circuit on the Logic Controller P.C. Board monitors and
maintains the CRT beam at its adjusted brightness. Refer to paragraph D in this
Section of the Service Manual for a functional description of the auto luminance
and microprocessor control circuits.
The necessary power to drive grid 1 of the CRT is supplied by the flyback
transformer. A low voltage output pulse from the secondary winding of the
flyback transformer gets converted into a negative dc voltage. This negative dc
voltage, in conjunction with the output drive network of the luminance circuit,
drives grid 1 of the CRT. Refer to the paragraph 4 in this Section of the Service
Manual for a functional description of how each component of the CRT is
powered.