Service; Introduction; Simplified Theory Of Operation; 7475A Simplified Block Diagram - HP 7475A Service Manual

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