TM 5-6675-324-14
Main drive circuit.
c.
When the COPY START key is depressed, a DRMD command is outputted from Q203-24 to
Q208, Q221 thru Q301, solid state relay driving the main motor.
d. Halogen lamp control circuit. The lamp regulator can provide two basic
levels of light intensity: Low level for blank exposure and a high level for
scanning exposure. The output is varied according to the amplitude of LINT voltage
from the dc controller printed circuit card. When LINT is low, light output is low
for blank exposure. When LINT is high, light output is high for scanning exposure.
When DRMD command is high, inverter Q208 causes Q221 to turn on and provide power to
activate the lamp regulator control circuitry. This power supply input is called
the IEXP command. Q3 and Q4 form a constant current source keeping the current thru
R18 constant. The output from bridge rectifier D2-D5 turns Q5 on, turning off Q6.
Q7 is biased on thru the voltage divider network consisting of R26, R17, and R3.
This allows C1O to charge. When a certain voltage is reached, PUT Q8 switches on,
and discharges C1O thru the primary winding of the PT. The pulse generated in the
secondary winding turns on Q1. After C1O discharges, Q8 turns off until the voltage
on C1O reaches the firing potential of Q8. The firing point can be synchronized
precisely with the same point on every cycle of ac supply to the lamp. Thus, the
circuit can control the switch on point of Q1 to provide equal power with varying
supply voltages or to vary the intensity of the light for various settings of the
exposure control lever. Q2 is turned on by the first pulse from Q8 and remains on
until power is secured. The controller basically acts as an analog computer keeping
the effective light output constant. The regulator circuit provides feedback volt-
ages (Sample V1 and Sample V2) from a voltage divider across a constant voltage
source consisting of R3 and Zener diodes ZD2 thru ZD4. The levels of Sample V2 can
be adjusted by VR1 and VR2 but, once set, their outputs remain constant. To provide
light for blank exposure, Sample V2 is connected directly to the input of the lamp
regulator via the normally closed contacts of K201 so that Sample V2 = LINT. During
3-12
