Service manual
CIRCUIT
THEORY
U5D
6532
+26 V
,
Pl
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R3
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J.
9 (CA
Hold!
~
3.9
k?
R5
P A
11--------,-13"....,
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.....
018
? 5 W
470
n
--
PAO
2 (HMO!
U7B
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CR22
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21
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U6D
U6B
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6522
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09
L
U6B
- -
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CA
Motor
PAl
5 (HM3)
71V
Carriage
Motor
Drive Circuits
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.
09-012
are
current
amplifiers. The phase A coil is energized
when
010
is turned on.
Current
is passed
through
the
center
tap
of
the
motor
coil,
through
018
to
the
26VDC
supply. The
other
three phases are controlled
the
same
way.
The
output
PA 1 (CA Hold) goes
"Iow",
and 0
18
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
09-012.
12