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Carriage Motor
Drive Circuits
+26 V
CIRCUIT THEORY
1
U6D outputs signals HMO-HM3 (HM stands for head motor>. Four outputs drive the four phases of
the stepper motor. This circuitry is similar to the paper drive motor circuits. Q9-Ql 2 are current
amplifiers. The phase A coil is energized when Q1 0 is turned on, Current is passed through the center
tap of the motor coil, through Qi 8 to the 26VDC supply. The other three phases are controlled the
same way. The output PAl (CA Hold> goes "low", and Qi 8 turns off when holding current is needed
to hold the paper in position. Two opposing phases are energized creating opposing torques holding
the motor in position. The holding currents from the motor coils return through R5 to the 26VDC supply.
R5 limits the current flow through the coils, CR13 through CR16 suppress the CEMF developed by
the coils in the motor protecting the output transistors Q9Q1 2.
U5D
6532
U6D
6522
MS
SW470fl
2 (HMO)
PAl
PAO
PAl
PA2
PA3
lkx
4
' 1t
g
3
4
—
U68
-I
11
10
068
068
U68
3 (HMI)
P1 ii
13 13
—
'1 21
2222
—
cm
Q9
'.4
CA Motor
12
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