Model 7475A
Section VI
SECTION
VI
SERVICE
6-1. INTRODUCTION
6-2.
This section contains information needed for main-
tenance
and
repair of
the
Model 7475A, including:
Circuit Description
Troubleshooting Information
Parts
Removal
and
Replacement
Cleaning
Schematic Diagrams
Component Location Figures
6-3. SIMPLIFIED THEORY OF OPERATION
6-4.
The
Model 7475A uses microprocessor-based logic
to convert digital instructions into a graphic plot. The
microprocessor receives instructions from either
an
inter-
nal
ROM program or
an
external controller through
the
I/O
(input/output) circuits.
It
then
issues
data
to
the
pen
drive
and
paper
drive motor servo systems
and
the
pen
down circuit to produce
the
plot. Figure
6-1
is
a simplified
block diagram
of
the
7475A plotter.
6-5.
The
two drive motors
are
reversible de motors.
Encoders
on
each
motor
transmit
rotation
data
back
to
their
respective servo IC. One motor drives grit wheels
which move
the
plotting medium, while
the
other motor
moves
the
pen across
the
plotting surface.
6-6.
There
are
two optional
I/O
(input/
output) circuits
available for the Model
7475A.
Option
001
is the RS-232-C/
CCITI'
V.24
serial interface. Option 002 is
the
HP-IB
(Hewlett-Packard Interface Bus) parallel
data
interface
which is compatible with
IEEE
standard
488-1978.
6-7.
RS-232-C/CCITI'
V.24
INTERFACE
CffiCUIT (Option
001)
6-8.
The Option
001
I/O
(Input/Output)
is
an
asyn-
chronous full-duplex bit-serial interface for hardwired
connection to a computer or terminal. Interface connec-
tions are shown on
the
schematic
diagram
at
the
end
of
this section. This interface is compatible with
EIA
Stand-
ard
RS-232-C
and
with CCITI'
V.24.
Input
and
output
are
controlled
in
the
7475A
by
the
Asynchronous
PEN
SIX
PEN
CAROUSEL
CAROUSEL
MOTOR
r------------------
DRIVER
MOT~R
~J
7475-A-12-1
CONTROLLER
POWER
SUPPLY
-5V
DATA
BUS
ADDRESS
BUS
ROM
24K
X 8
RAM
2K
XS
+12V
FRONT
PANEL
CONTROL
&
+22V
INDICATORS
-12V
(RS-232-C
ONLY)
GATE
ARRAYS
MOTOR
DRIVER
SERVO
IC
Figure
6-1.
7475A Simplified Block Diagram
PEN
SOLENOID
PAPER
DRIVE
MOTOR
~"
............
/
OPTICAL
ENCODER
0
6-1
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