Repair manual

2-64
THEORY OF OPERATION
secondary windings. The high voltage pulse from the secondary windings
of the flyback transformer is then applied to a high voltage rectifier. This
high voltage rectifier converts the developed high voltage pulse to a DC
voltage of +8.5 kilovolts. This converted voltage drives the anode of the
CRT.
When the Digital Palette is turned off, the high voltage supplied to the
anode of the CRT shuts off. A bleeder resistor in its associated circuitry
slowly discharges the high voltage stored by the internal capacitance of
the CRT.
b. +35 VDC
This voltage, in conjunction with the Cathode Driver circuit, drives the
CRT cathode. When the Horizontal Deflection circuit applies a flyback
pulse to the primary winding of the flyback transformer, a low voltage
output pulse from tap 4 of the flyback transformer secondary winding is
applied to a voltage rectifier. The voltage rectifier converts the low
voltage output pulse into a positive dc bias voltage. This positive dc bias
voltage drives the CRT cathode. Refer to paragraph 5 in this Section of
the Service Manual for a functional description of the Cathode Driver
circuit.
c. -130 VDC
This voltage, in conjunction with the Luminance (brightness) circuit,
drives grid 1 of the CRT. The Luminance circuit, in conjunction with the
COARSE and FINE LUMA (brightness) controls (R46 and R47), adjusts
the current flow through grid 1 of the CRT. Adjusting the current flow
through grid 1 controls the brightness of the beam when the CRT is turned
on. Once the COARSE and FINE LUMA controls are properly adjusted
for a specified brightness, the Auto Luminance circuit on the logic
Controller P.C. Board monitors and maintains the CRT beam at the
adjusted brightness.
During horizontal retrace, a low voltage output pulse from tap 3 of the
flyback transformer secondary winding is applied to a voltage rectifier.
The voltage rectifier converts the low voltage output pulse into a negative
dc voltage. This negative dc voltage drives grid 1 of the CRT. The
converted dc voltage is applied to the auto luminance output driver
network. The COARSE and FINE LUMA (brightness) potentiometers
R46 and R47 controls the beam brightness by changing the bias on grid 1
of the CRT. A more negative bias decreases electron flow, turning down
the brightness. Refer to paragraph 6 in Section D of this Service Manual
for a functional description of the Auto Luminance circuit.