TM 11-6625-3025-14/ET426-AA-MMA-010/E154 VII210/T.O. 33A1-8-902-1-1
4-11. Power Regulation. (See figure FO-19). The power supply employs three separate voltage regulator circuits:
+12vdc, +5vdc and -5vdc. The regulators are mounted on a heat sink filter assembly located on the inside rear panel of
the cabinet. The +5v and -5v supplies operate from the same transformer (T1) windings with diodes (CR1-CR4) polarity
providing positive and negative dc voltages as desired. A separate winding is provided for the +12v supply regulator (Z1) .
Diodes CR1 and CR2 and filter capacitor C8 (located on the heat sink filter assembly) develops a dc level of about
+17v reduced by positive regulator Z1 on the rear panel to +12v. This rectifier is kept lightly loaded to keep ripple valleys
well above possible regulator dropout levels.
Diodes CR3 and CR4 and filter C7 on the rear panel heat sink develop a negative voltage of about -17v which is
reduced by negative regulator Z3 to -5v.
The regulated +12v is used as a reference to operate a precise low ripple (1 mv or less) +5v to operate voltage
controlled astable multivibrators which develop the test pattern circuit elements. The +12v dc level is routed through
dropping resistor R4 (pin Y) on the power regulator circuit card to zener diode CR5. This reference level is then routed
through an adjustable voltage divider (R1) to one side of transistor pair circuit Q2 and Q3. The adjustable voltage at the
base of Q3 develops a reference level through the emitter of Q3 to resistor R5. The +5v level is fed back into the base of
Q2 to establish a base-to-emitter bias level for controlling the current through load resistor R6. This, in turn, controls the
collector voltage for amplifier Q2, which feeds a controlling level to the base of Q1 to the base of power regulator transistor
(Q1) mounted on heat sink assembly. From the emitter of the power transistor (Q1), voltage is distributed throughout the
unit, and is returned to the power regulator card as a very precise +5v reference level which exhibits less than 1 millivolt
ripple.
4-19/(4-20 blank)
