Motorola R-2001A Service Manual page 170

16-1. General. Bias and drive voltages for the CRT are supplied by the High Voltage Supply. The supply
converts a nominal 8 VDC input level to output voltages of +4 kV and -2 kV. Circuits for low voltage control of
the intensity and focus grids is also provided. A block diagram of the High Voltage Power Supply is shown in
figure 16-1 and its schematic in figure 16-2.
16-2. High Voltage Supply. A nominal 8 VDC level at the center tap on the high voltage transformer is
switched through the primary winding by the chopper at a 20 kHz rate. Q4/Q6 BASE DRIVE signals from the
Low Voltage Supply drive the Chopper circuitry. The secondary of the transformer is a 1 KV winding that is
quadrupled to a nominal +4 kV and is doubled to a nominal -2 kV. A separate 6.3 V winding provide the CRT
heater drive.
16-3. The-2 kV is regulated by comparing a sample of that voltage to the7.9VREFsignal.The resultant error
signal (HV CONTROL) controls the level of the DC input to the high voltage transformer.
16-4. A Bias Divider circuit on the primary center tap provides the operating potential for the Q4/Q6 drive
winding in the low voltage power supply.
16-5. Intensity and Focus Control. An 87V zener diode and resistive divider provide the intensity and focus
voltages. The modulator circuits provide variable output voltages within their bias ranges under the control of
the low voltage INTENSITY/FOCUS TV inputs.
16-6. DC control loops are utilized to stabilize the gird and focus voltages. For the intensity circuit the
INTENSITY SAMPLE and HV REF signals are compared, on the Scope Amplifier Module, with the control
input. The result of the comparison is the INTENSITY TV drive signal to the modulator. The focus voltage is
controled in the same way, except the HV REF signal is not used in the comparison.
SECTION 16
HIGH VOLTAGE POWER SUPPLY (A10)
16-1