TM 5-6675-323-14
a i . Main PCA A2 motor driver circuitry. T h e m o t o r d r i v e r c i r c u i t r y p r o v i d e s
amplification of the interpolator outputs required to drive the X- and Y-axis
stepper motors and the paper advance motor, if installed.
(1) Following the path of the X cosine signal, from the buffer U1C, the
signal passes through the mute switch S1. This switch allows for muting of the X-
axis motor during servicing or alinement procedures.
(2) The first stage of the X cosine motor driver is U5 which functions as a
h i g h g a i n i n t e g r a t o r t o t h e s i g n a l . T h e 10 kHz oscillator signal from the power
supply is also input at this stage to develop the required triangular switching
signal.
Feedback from the motor is also sensed here for precision current control.
The offset potentiometer is used to establish the baseline reference for the drive
signal.
I n the X- and Y-phase A amplifiers, the gain potentiometers allow matching
of-the relative gains of phases A and B.
( 3 ) T h e t r i a n g u l a r o u t p u t o f U 5 , p l u s t h e s i g n a l , i s a p p l i e d to the compara-
tor U11 along with a feedback signal from-the motor. The resulting squarewave
output has an amplitude of approximately 25 volts.
(4) During power-up and the paper advance switching sequence, the U11 output
i s d i s a b l e d b y t h e c o n d u c t i o n o f t r a n s i s t o r Q 5 . T h e ZPWR signal is used to turn on
Q5. The resistor R23 in the feedback path acts as a current sensing resistor. This
provides a convenient location for testing circuit action.
3-133
