TM 5-6675-320-14
a.
Motor driver PCA A8.
Houses the pen solenoid driver and the X/Y-drive
a m p l i f i e r s .
The motor driver PCA may be functionally divided into two circuit sections:
Current amplifier circuit for each of four motor phase
drive signals (X-sine, X-cosine, Y-sine, and Y-cosine)
Pen relay drive amplifiers
NOTE
Except for the addition of a GAIN control to the X- and Y-sine amplifier
c i r c u i t , t h e f o u r a m p l i f i e r c i r c u i t s a r e i d e n t i c a l . C o n s e q u e n t l y , o n ly
the X-sine amplifier will be described here.
( 1 ) C u r r e n t a m p l i f i e r c i r c u i t .
The selected output of the motor phase ampli-
fier, located on PCA A5, is coupled into its respective amplifier circuit through
connector J5.
A separate mute switch is provided for each axis to disconnect the
input to the amplifier to enable service and calibration .
In each phase, the first
amplifier stage (U1 and U2) functions as an active low pass filter with a cutoff
point at 600 Hz.
Assuming the sine amplifier has been selected, the motor drive
s i g n a l i s a p p l i e d t o t h e i n p u t o f a c t i v e f i l t e r U 1.
The setting of GAIN control R6
determines the amplitude of the input motor drive signal that is applied to the
i n v e r t i n g i n p u t o f o p e r a t i o n a l a m p l i f i e r ( f i l t e r ) U 1 . O f f s e t c o n t r o l R 8 d e t e r m i n es
the zero or reference level for the output of U1.
( 2 ) P e n r e l a y d r i v e a m p l i f i e r s.
Produce bias voltages applied to pen power
transistors and send power to drive pen solenoid.
When the polarity of the output
at U1 is positive, it causes transistors Q1 and Q3 to conduct, resulting in a
proportional positive output through connector J1-6 to power transistors Q5 and Q6
located on PCA A12.
Transistors Q5 and Q6 drive the X-motor sine winding. A fuse
F1 is installed in series with the motor winding to protect it in the event that
either power transistor Q5 or Q6 on PCA A12 should develop a short circuit condi-
t i o n .
Resistor R11 acts as a motor current sense resistor.
NOTE
I t i s a c r o s s t h i s c u r r e n t s e n s e r e s i s t o r t h a t t h e a c t i o n o f t h e c i r c u i t
and the effect of the circuit control adjustments can be best measured.
When the polarity of the output of U1 is negative, it causes transistors Q2 and Q4
to conduct, resulting in a proportional negative output to connector J1-6 and the
power transistors Q5 and Q6 on PCA A12.
The motor sine winding is thus driven in
the opposite direction (from when the polarity is positive) .
The remaining three amplifier circuits
an identical manner.
( X - c o s i n e , Y - s i n e , a n d Y - c o s i n e ) o p e r a t e in
4-35
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