Radio Shack TRS-80 User manual

Radio /haek
Service
THIS BELONGS TO SHOP #7714
RADIO SHACK COMPUTER CENTER
CHATHAM PLAZA SAVANNAH, GA 314(36
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ILINE PRINTER
Catalog Numbers
26-1150
and
26-1152

NOTE
The purpose of this manual is twofold. It provides the owner with complete
adjustment procedures and it provides Radio Shack Service Personnel with
complete repair procedures.
If you are not technically inclined, do not attempt to repair your Printer. If
you do, you'll void your warranty.

TABLE OF CONTENTS
SECTION PAGE
SECTION 1
INTRODUCTION
1.1 General Description 1-1
1.2 Printer Operation 1-1
1.3 Specifications Summary 1-3
SECTION 2
THEORY OF OPERATION
2.1 Introduction 2-1
2.2 Block Diagram Discussion 2-1
2;3 Initializing the Printer 2-2
2.4 Data Input 2-3
2.5 Character Printing 2-3
2.6 Carriage and Ribbon Movement 2-5
2.7 Paper Motion 2-6
2.8 Power Supplies 2-7
SECTION 3
PRINTER ASSEMBLIES
(REMOVAL/REPLACEMENT AND ADJUSTMENT PROCEDURES)
3.1 Introduction 3_1
3.2 Printer Subassemblies 3_1
3.3 Cover Assemblies 3.5
3.4 Print Head Assembly 3.6
3.5 Video Amplifier Assembly 3.7
3.6 Ribbon Cartridge Assembly 3.9
3.7 Carriage Assembly 3_10
3.8 Drive Motor Assembly 3_1
2
3.9 Platen Drive Assembly 3.13
3.10 Platen Assembly 3_15
3.11 Pinch Roller Assembly (26-1150) 3-17
3.12 Column Scale/Tear Bar Assembly 3_19
3.13 Tractor Drive and Pin Feed Assemblies (26-1 152) 3-20
3.14 Control Panel Assembly 3. 22
3.1 5Primary Voltage Assemblies 3.23
3.16 Electronic Module Assembly 3. 25
3.1 7Logic Board Assembly 3.26
3.18 Hardware Kit 3.28
3.1 9Special Tools 3.28
SECTION 4
MAINTENANCE
4.1 Recommended Tools 4_1
4.2 Preventive Maintenance 4_2
4.3 Troubleshooting Guide 4.3
4.4 Engineering Drawings 4.3
APPENDIX A
PARALLEL INTERFACE SPECIFICATIONS
APPENDIX B
SIGNAL GLOSSARY

LIST OF ILLUSTRATIONS
FIGURE PAGE
1-1 Line Printers 1-1
1-2 Basic Block Diagram 1-1
1-3 Character Printing/Paper Motion 1-2
2-1 Simplified Block Diagram, Electronics 2-1
2-2 Initializing the Printer 2-2
2-3 Data Input 2-3
2-4 Character Printing 2-4
2-5 Carriage and Ribbon Movement 2-5
2-6 Paper Motion 2-6
2-7 +5 VDC Power Supply 2-7
2-8 -12 VDC Power Supply 2-8
2-9 +35 VDC Power Supply 2-8
3-1 Printer Subassemblies 3.
2
3-2 Cover Assemblies 3.4
3-2A Print Head Assembly 3-6
3-3 Penetration Control Adjustment, Print Head Assembly 3-7
3-3A Kit, Video Amplifier Assembly 3-8
3-3B Kit, Ribbon Cartridge Assembly 3.9
3-4 Carriage Assembly, Removal/Replacement 3-10
3-5 RTPand EOP Actuator Arm Adjustments 3-11
3-5A Kit, Drive Motor Assembly, Removal/Replacement 3-12
3-6 Drive Motor Assembly Adjustments 3-13
3-6A Kit, Platen Drive Assembly 3. 14
3-7 Platen Drive Assembly, Adjustments 3_14
3-7A Kit, Platen Assembly 3_1
6
3-8 Platen Assembly Adjustment 3-16
3-8A Kit, Pinch Roller Assembly (26-1150) 3-18
3-8B Column Scale/Tear Bar Assembly 3_19
3-8C Tractor Drive and Pin Feed Assembly (26-1 152) 3-20
3-8D Tractor Drive Timing Belt Tension (26-1 152) 3_22
3-8E Paper Travel Adjustment, Tractor Drive (26-1 152) 3-22
3-8F Control Panel Assembly 3.23
3-8G Kit, Primary Voltage Assembly 3.24
3-8H Electronic Module Assembly 3.25
3-8 1Kit, Logic Board Assembly 3_26
3-9 Deleted
3-10 Deleted
3-1
1
Line Lengths 3.27
3-12 Kit, Special Tools 3_28
4-1 Schematic Diagram, Electronics Board 4.4
4-2 Schematic Diagram, Video Amplifier 4.5
4-3 Wiring Diagram, Printer 4.6
4-4 Wiring Diagram, Primary Voltage 4.7
Assembly Diagram, Electronics Board 4.8
4-5
4-6 Assembly Diagram, Video Amplifier 4.9

SECTION 1
INTRODUCTION
This Service Manual describes two Line Printers (Catalog Numbers 26-1150 and 26-1152) that are manufactured for Radio
Shack. The manual provides ageneral description of the units, followed by amore detailed theory of operation and spare
parts information enabling field engineering personnel to service these printers. The manual is aimed at subassembly level
maintenance.
For convenience. Operator's Manuals are published separately which describe all operator controls and functions. This Service
Manual is subdivided into the following sections, each with its specific purpose.
SECTION 1-INTRODUCTION, presents the scope and content of the manual and provides the reader with ageneral
description of the printer.
SECTION 2-THEORY OF OPERATION, provides adescription of each functional operation in the printer, based on
asubassembly level.
SECTION 3-PRINTER ASSEMBLIES: REMOVAL/REPLACEMENT/ADJUSTMENT, contains afunctional descrip-
tion, removal/replacement/adjustment and maintenance procedures for each replaceable subassembly in
the printer.
SECTION 4-MAINTENANCE, includes preventive maintenance and troubleshooting procedures, as well as schematic
and wiring diagrams of the printer.
APPENDIX A-PARALLEL INTERFACE SPECIFICATIONS, contains detailed information describing the standard
interface timing signals, connectors and other specifications.
APPENDIX B-SIGNAL GLOSSARY, provides atable of signal names, by mnemonic code, keyed to the Line Printer
Electronics Board Schematic Diagram.
NOTES
The TRS-80 Line Printers are just two of aseries of Line Printers. It is the intent of this manual to provide
information only for the TRS-80 Line Printers. These printers are basically the same; the primary difference is
in the type of paper feed assemblies. The 26-1150 printer has apinch roller assembly and the 26-1152 has a
tractor drive assembly. Where applicable, aprocedure or description pertaining to either paper feed mechanism
will be identified by Catalog Number.
Part Numbers refer to the Manufacturer's Part Number, which may be obtained directly from Radio Shack's
National Parts Department.
Ill

1.1 GENERAL DESCRIPTION (Figure 1-1)
The printers shown in Figure 1-1 are 60 character-per-second, uni-directional impact printers with an effective throughput of
21 to 90 lines per minute at 10 characters per inch; and up to 132 columns of operator variable density (10 to 16.5 characters
per inch). The pinch roller (26-1150) unit prints in 8inch lengths on roll paper up to 9.8 inches (250 mm) wide, while the
tractor drive model (26-1152) prints in 8inch lengths on paper 12.1 inches (307 mm) wide.
PINCH ROLLER
(26-1150)
TRACTOR FEED
(26-1152)
Figure 1-1. LINE PRINTERS
Characters are formed in a5x7 dot matrix. In addition to the standard ASCII, avariety of character sets give great flexibility
in character formation. The printer will accommodate up to 64 characters.
All the electronics, including logic driver circuits and power supplies, are contained on asingle printed circuit board.
1.2 PRINTER OPERATION
The printer contains aline buffer which allows parallel data to be received at rates up to 75,000 characters per second. A
basic block diagram of the printer is shown in Figure 1-2.
CONTROL
PANEL
t
CONTROL
1. PRINT COMMAND
(CROR LAST CHAR.
1
2. PAPER MOVEMENT
(LINE FEED)
3. SPECIAL FUNCTIONS
(MOTOR CONTROLI
HEAD MOTION CONTROL CARRIAGE
ACTIVATOR
SOLENOIDS
DATA PAPER MOTION CONTROL LINE FEED
SOLENOID
INPUT
TIMING
*
LINE
BUFFER CHARACTER
GENERATOR WRITE PRINT
HEAD
PULSES
Figure 1-2. BASIC BLOCK DIAGRAM
Basically, all printer functions can be grouped into one of two categories: (1) character printing, and (2) paper motion.
1-1

1.2.1 CHARACTER PRINTING (Figure 1-3)
Line Printer characters are printed by selectively activating the seven print wires aligned in avertical column in the print
head. As the print head moves across the paper, the appropriate print wires are momentarily activated driving them against
the ribbon, paper and platen to form the specified dot pattern.
The print commands to the seven print wires are developed by the read-only-memory (ROM). Avariety of character sets is
obtainable simply by changing the ROM. Each character within aROM is addressed by a7-bit character code and each
column within acharacter is specified by timing signals internal to the printer.
As shown in Figure 1-3, the print head and ribbon cartridge are attached to the carriage assembly. By activating either of the
two carriage solenoids, the carriage attaches to acontinuously rotating band. Activating the forward carriage solenoid attaches
the carriage to the upper half of the band and moves the print head in the forward (left to right) direction. Activating the
reverse carriage solenoid, attaches the carriage to the lower half of the band and moves the head in the reverse direction.
PRINT HEAO
PLATEN
KNOB
-DRIVE MOTOR
Figure 1-3. CHARACTER PRINTING/PAPER MOTION
1.2.2 PAPER MOTION
Paper can be moved manually by pushing in and rotating the platen knob, or automatically by performing aline feed opera-
tion.
As shown in Figure 1-3, power from the drive motor is applied via aline feed clutch to the platen and forms handling mech-
anism (pinch roller or tractor) drive gears. Paper is advanced one line by momentarily activating the paper motion solenoid in
the line feed clutch, allowing the drive gears to turn and advance the paper by one line.
1.2.3 SPECIAL FUNCTIONS
In addition to printable character codes, the printer also recognizes four special control codes-. Refer to subsection 2.4.2 for
these control codes and the printer action performed upon receiving these codes.
1-2

1.3 SPECIFICATIONS SUMMARY
DATA INPUT
Data Format 7bit ASCII parallel
Input Code 64 character ASCII
Data Rate Up to 75,000 characters per second
Buffer One-line character buffer (up to 132 characters)
Input Gating Data Strobe is normally gated with acknowledge of previous
character.
PRINTING
Printing Method Impact, character-by-character, unidirectional
Dot Matrix 5x7
Print Format 10 to 16.5 characters per inch (operator adjustable)
Print Rate 60 characters per second at 10 cps
100 characters per second at 16.5 cps
Number of Copies
26-1 150 Prints original and one carbon copy
261 152 Prints original and up to four carbon copies
Character Set Standard 64 character ASCII. Optional 5x7, 64 character sets
available
PAPER ADVANCE
Vertical Format 6lines per inch
Paper Entry Rear Paper Feed
Auto Line Feed Automatic line feed on carriage return. Disable by option
Paper Feed
26-1150 9.8 inches (250 mm) wide paper
26"1152 12.1 inches (307 mm) maximum width
10.2 inches (259 mm) maximum print width
CONTROLS/INDICATORS
Switches Print and Power
Indicators Power
Manual Controls Forms Thickness, Paper Advance, Print Density
PHYSICAL/ENVIRONMENTAL/ELECTRICAL
Height 8inches (203 mm)
DePth 19.5 inches (495 mm)
Width 19.8 inches (503 mm)
Weight 45 lbs (20 kg)
Temperature
Operating 40° to 100°F (4.4° to 37.7°C)
Storage _40° to 140°F (-40° to 60°C)
Humidity
Perating 20% to 90% (No condensation)
Storage5% to 90% (No condensation)
Input Voltage 60 Hz, 120 VAC
1-3

SECTION 2
THEORY OF OPERATION
2.1 INTRODUCTION
This section contains adescription of each major function performed by the Line Printer electronics. This section is organ-
ized as follows:
2.2 Block Diagram Discussion
2.3 Initializing the Printer
2.4 Data Input
2.5 Character Printing
2.6 Carriage and Ribbon Movement
2.7 Paper Motion
2.8 Power Supplies
Each function is discussed at asubassembly level, supplemented with block diagrams showing signal flow between major
subassemblies and the connector/pin locations of each signal. Figure 2-1 is asimplified block diagram of the overall printer
electronics.
"1
1
1ELECTRONICS BOARD
1
POWER
DRIVERS 1
1>MEMORY
(RAMI
f
>CHARACTER
GENERATOR
(ROM)
K\
INTERFACE
CONNECTOR 1
1
DATA 1-DATA 7>>CG1-CG7 >PRINT HEAD
'LV/*- jVSOLbNUtUS
ADDRESS TIMING
INPUT
CONTROL
LOGIC
LINES
DATA INPUT (OATA l-DATA 71 —
^
LF orCR
1
1
1
1
1
1
DATA STROBE ADDRESS
COUNTER
STROUT PRINT
CONTROL
LOGIC
HEAD MOTION \CIP.CIR 1T
1
1
1
i
1
1
I
DSTA y
PRINT
ACKNOWLEDGE.BUSY
COMMAND ITIMING
INPUTS LINE FEED
SITY
PMSOL 1T0
1
1
i
'
i
1
1
OCSILLATOR 5DEN
L
CONTROL
PANEL MARGIN
INDICATOR'S
Figure 2-1. SIMPLIFIED BLOCK DIAGRAM, ELECTRONICS
NOTE
THE NOTATION (N) AFTER ASIGNAL MNEMONIC IS USED TO INDICATE THE "NOT" OR INVERSE
FUNCTION OF THE SIGNAL. FOR EXAMPLE: CIP (N) IS THE NOT FUNCTION OF THE CIP SIGNAL. THE (N)
NOTATION IS EQUIVALENT TO THE BAR APPEARING OVER ASIGNAL AS SHOWN ON THE SCHEMATIC.
2.2 BLOCK DIAGRAM DISCUSSION (Figure 2-1)
The unit is aunidirectional printer, whose print head moves to the right when printing and left when returning the carriage.
The seven print wires in the print head are selectively activated to form the dot matrix pattern for the specified character.
The print commands to the seven print wires are developed by the character generator which consists of aread-only-
memory (ROM). Attached to the carriage assembly are the print head and ribbon cartridge. By activating either the forward
or reverse carriage solenoid the carriage attaches to acontinuously rotating fibre band. The forward solenoid is activated
during the print cycle and the reverse solenoid is activated to return the carriage. Paper is advanced one line by momentarily
activating the paper drive solenoid in the line feed clutch unit.
The Line Printer electronics is contained on one printed circuit board. As shown in Figure 2-1, printable data goes from left
to right across the diagram to the print head, with control of this data coming from the input control logic and the print
control logic. When the printer is first turned on, the printer logic is initialized and the printer is not print enabled. To receive
data, the printer must then be enabled by depressing the PRINT rocker switch on the operator's panel.
2-1

If the printer is print enabled and not busy, the input data is loaded into the printer by the data strobe from the input device.
The printer responds with an acknowledge pulse to acknowledge reception of the data. Printable data, after being inverted
by the input gating, is loaded into the Random Access Memory (RAM), consisting of two 4-bit by 256 maximum character
memories. The address counter generates the seven address inputs for the RAM.
Printable data will continue to be loaded until the memory is filled or acarriage return control code is received by the printer.
In either case, the printer goes busy and starts the print cycle by activating the forward carriage solenoid (CIP). This attaches
the carriage to the rotating band, moving the carriage from left to right across the page. The address counter is clocked
(STROUT (N)) to address the appropriate location in memory for the character to be printed. The character is translated by
the character generator (ROM), which generates the impulse signals to drive the head solenoids.
At the end of the printed line, the forward solenoid is deactivated and the reverse solenoid (CIR (N)) is activated to return the
carriage to the left margin. The printer remains busy until the end of the print cycle. Also at the end of the line, the paper
drive solenoid is momentarily activated, causing the paper to advance by one line.
When the carriage has returned to the left margin, the reverse solenoid is deactivated, the busy signal goes away, the
acknowledge signal is generated, and the next line of data is taken in.
The left margin indicator (RTPSW) signals the logic when the carriage reaches the extreme left margin of the printer. As
the carriage moves, the oscillator (ME1) provides the control for print timing.
2.3 INITIALIZING THE PRINTER (Figure 2-2)
Before the printer can accept data, it must be power primed, paper loaded and print enabled. The power prime operation
initializes the printer logic to aready state. The print enable operation, resets the busy line to the interface connector and
makes the printer ready to receive data.
2.3.1 POWER PRIME
The power prime signal (PWRPRM (N)) is generated when the power switch is turned on. The (PWRPRM (N)) signal gen-
erates the (EOPPRM (N)) signal which clears the print control logic.
2.3.2 PRINT ENABLE
Before the printer can receive data, it must be enabled. This can be done by depressing the PRINT switch on the operator's
panel.
2.3.3 PAPER EMPTY
With paper loaded in the printer and the printer is power primed and print enabled the printer can receive data. If paper is
not loaded in the printer or a paper empty condition exists in the printer, the paper empty switch opens, causing aBUSY
signal to the input device. Apaper empty condition is detected in the printer by the paper empty switch located in the path
of the paper. ri
ELECTRONICS BOARD
rCONTROL PANEL
ItEL^/3~SELRET
3
PRINT O-
SWITCH
L.
PAPER EMPTY SWITCH
I
P003 JCKJ3
-Q-CD
INPUT
CONTROL
LOGIC
PRINT
CONTROL
LOGIC
-ED—cm
I
I
I
I
L_.
C5
20ufd
0V- ^
CR4 Jp
IN4002J&
j,ME13
L5V-
R26
4.7K< R27
4.7K<
J
Figure 2-2. INITIALIZING THE PRINTER
2-2