Radio Shack TRS-80 User manual

·-
•
erv1ce
TRS-BO ®
Color Computer 2
Catalog Number 26-3026/7
CUSTOM MANUFACTURED IN U.S.A. BY RADIO SHACK, A DIVISION OF TANDY CORPORATION

-----------TRS-80 ® -----------
TRS-80® Color Computer 2 Service Manual
Copyright~ 1983 Tandy Corporation
All Rights Reserved
Reproduction or use, without express written permission from
Tandy Corporation, of any portion of this manual is
prohibited. While reasonable efforts have been taken in the
preparation of this manual to assure its accuracy, Tandy
Corporation assumes no liability resulting from any errors
or omissions in this manual, or from the use of the
information contained herein.
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Color Computer 2
TRS-BO ®
Service Manual
TABLE OF CONTENTS
1/ General
1.1
1. 2
1. 3
Introduction •......
System Description ...... .
Memory Map . ............. .
2/ Specifications
2.1
2.2
2.3
Physical..
Power .....
Technical.
3/ Disassembly/Assembly
3.1
3.2
3.3
Disassembly ......... .
Assembly . ....•...........
64K Upgrade Instructions.
4/ Theory Of Operation
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.15
MC6809E
CPU ...
Reset
Circuit ..
Memory ....... .
Video Generation Circuitry.
Artifacting ............ .
PIAs ....•
ROM • •••••
Keyboard Interface ..
DAC Circuitry ..... .
SALT Circuitry .•........•.••.
Cassette Tape Format Information ..
RS232 Connector (J3)
Cartridge Connector (J6).
Power Transformer ......... .
Joysticks ...... .
4.16 TV Switch Box .•.
Schematic 8000191, Color Computer.
Component Layout 1700235, Main Logic Board 8857636.
Circuit Trace, PCB 8857636, Component Side ....... .
Circuit Trace, PCB 8857636, Solder Side ..
Parts List, PCB 8857636 ................ . .•..
1
1
6
13
13
13
15
16
18
19
26
27
31
34
36
39
39
41
44
48
49
51
55
55
56
57
61
63
65
67
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Color Computer 2
-----------TRS-BO ®
Service Manual
5/ Troubleshooting
5 .1 Introduction . ...................................... .
5. 2 Video Problems .. ................................... .
5.2.1 No Display ....................................... .
5 . 2 . 2 No Sync ..........•..................•..•.......•..
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
"Garbage" on Screen .............................. .
Clear Screen, No Signon ..................•••......
No Color . ........................................ .
Wrong
Colors . .................................... .
No Artifacting Or Improper Artifacting ........... .
5. 3 Keyboard . .......................................... .
5.3.1 No Keyboard Entry ..............................•..
5.3.2 Some Keys Inoperative~ ........................... .
5. 3. 3 Wrong Character for Key Pressed ...............•...
5. 4 Processing Problems . ............................... .
5.4.l General .......................................... .
5.4.2
5.5
5.5.l
5.5.2
5.5.3
5.6
5.6.1
5.6.2
5.7
5.8
5.9
5.10
Symptoms ......................................... .
Cassette Problems . ................................. .
Motor Control Problems .........•....•....•........
Write Problems .. ................................. .
Read Problems .. .................................. .
RS 232 Problems . .................................... .
Output Missing or Incorrect ...................... .
Input Problems . .................................. .
Sound Problems . .................................... .
Joystick Problems .................................. .
Cartridge Problems . ................................ .
Power Supply . ...................................... .
6/ Exploded View/Parts List
71
72
72
73
73
74
74
75
75
76
76
76
76
77
77
77
80
80
80
81
81
81
82
82
82
83
83
Exploded View ....................................... 98
Parts List .......................................... 99
Appendices
MC6809E Data Sheet (Motorola DS9846-Rl)
SN74LS783 Data Sheet (Motorola ADI-595)
MC6847 Data Sheet (Motorola DS9823)
MC6821 Data Sheet (Motorola DS9435-R2)
MC6822 Data Sheet (Motorola ADI-938)
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ii

,..
.·
Color Computer 2 Service Manual
-----------TRS-BO ® -----------
Fig.
1-1
1-2
1-3
3-1
3-2
3-3
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
4-12
4-13
4-14
4-15
4-16
4-17
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
5-10
5-11
5-12
5-13
5-14
Description
Color
Computer
2
Color
Computer
2
Color
Computer
2
Color Computer
2
Color Computer
2
Color Computer
2
Color Computer
2
LIST OF FIGURES
Page No.
Installation.................... 2
Block Diagram................... 4
Memory
Map (Page 1). . . . . . . . . . . . . 6
Memory
Map (Page 2)............. 7
Memory
Map (Page 3)............. 8
Memory
Map (Page 4) ............. 10
Memory Map C Page 5). . . . . . . . . . . . . 11
Shield Clip Location ............................. 16
Power Cord Strain Relief ......................... 17
64K Upgrade. . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . 18
MC6809E Programming Model ........................ 20
MC6809E Pin Assignments ..•....................... 23
MC6809E
Read/Write Timing at 0.895 MHz ........... 25
MC6883
Reset Circuitry ........................... 26
DRAM Block Diagram ............................... 28
DRAM Timing...................................... 29
Color Computer 2 Address Decoding ................ 31
Color Computer 2 Artifacting Circuitry ........... 35
PIA Block Diagram................................ 37
Color Computer 2 Keyboard Array .................. 40
DAC Block Diagram................................ 42
SALT Block Diagram ............................... 45
Color Computer 2 Power Supply .................... 46
I/O Circuitry.................................... 47
RS-232C Connector Pin-Out ........•....•.......... 49
Joystick Schematic............................... 55
Antenna Switch Box Schematic ..................... 56
Normal Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Defective Power Supply ........................... 88
High Frequency Component of +5V Source ........... 89
E and Q Clocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
VDG Clock and Modulator Clock .................... 90
Y and Phase B... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Phase Band Phase A Relationships, Green Screen .. 92
Phase Band Phase A Relationships, Blue Screen ... 92
Phase Band Phase A Relationships, Red Screen .... 92
Artifacting Signals.............................. 93
Artifacting Signals.............................. 93
Artifacting Signals.............................. 93
Address Lines (Typical) .......................... 94
Data Lines (Typical) ............................. 94
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Color Computer 2 Service Manual
-----------TRS-80 ® -----------
LIST OF FIGURES (con't)
Fig. Description
Page No.
5-15
5-16
5-17
5-18
RAS* and CAS* ................................... .
Data IN and Data OUT ........••••.................
Sound and Cassette Output ....................... .
Cassette Zero Crossing Detector ................. .
95
95
96
96
6-1 Color Computer 2 Exploded View ................... 98
LIST OF TABLES
1 Line Printer variables ...................•....... 51
2 Alternate Line Printer Variable Values .......•... 52
3 Cartridge Connector Signals...................... 53
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iv

Color Computer 2
-----------TRS-BO ®
1/ General
1.1 Introduction
Service Manual
The Color Computer 2 is a refined version of Radio Shack's
popular Color Computer. It is designed to provide the same
reliable operation as its predecessor, but incorporates the
latest in electronic technology. Interconnection to a video
monitor, printout device, or modem provides maximum
versatility of the Color Computer 2. Figure 1-1 shows a
typical installation of the Color Computer 2.
Interconnecting cables are noted which provide signal and
control transfer between the major components. Always
remember to remove all power from the Color Computer 2 prior
to installing any peripheral device to prevent damage to the
device or the Color Computer 2.
The Color Computer 2 contains an internal BASIC program in
ROM which is accessed when the unit is powered up. Other
program modules/cartridges may be inserted into the
receptacle at the right side of the unit. An optional
Multipak Interface module allows up to four program paks to
be installed at the same time with selection of the specific
module active at any one time selected either by software or
by a switch on the Multipak Interface module. Additional
peripheral devices, such as an external disk drive, may be
added to the Color Computer 2 for additional memory storage
and retrieval.
All inputs to or outputs from the Color Computer 2, with the
exception of the program module/cartridges, are contained on
the rear panel of the unit. These include the joystick
inputs (right and left), Serial I/O, Cass I/O, TV output
connector, Power ON/OFF switch, and RESET switch. A
recessed channel switch (for selecting either channel 3 or 4
on the TV) is also located on the rear panel of the unit.
1.2 System Description
The primary functions of the Color Computer 2 are performed
by five 40-pin Large Scale Integration (LSI) chips plus
Random Access Memory CRAM) and Read Only Memory CROM).
These five chips are labeled on the Block Diagram as CPU,
SAM, VDG, and two PIAs. With only these five chips plus
RAM, ROM, and a power supply, the Color Computer 2 will
operate and provide a composite video output. However, to
allow communication with the outside world, I/O interfaces
must be added.
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Color c ornputer 2
COLOR
MONITOR
LEFT JOYSTICK
Figure 1-1.
TRS-BO ®
anual
-
--------~S~e=r~v~i:c:e_~~~~~
RIGHT JOYSTICK
Color c ornputer 2
Installat'
ion
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__ c _o_ 1 _o_ r_ c_o_m_p_u_t_e_r_ 2 ____ TRS - BO ®
Service Manual
The main component of any computer system is the Central
Processor Unit (CPU, U23). It is the function of the CPU to
provide or request data and select the proper address for
this data. In addition, the CPU is capable of performing a
limited set of mathematical and logical operations on the
data .
ROM (Ul2 + Ul3 in Extended Basic) has the function of
providing the CPU with a pre-defined set of instructions.
Without ROM, the CPU would run wild and randomly execute
instructions. In normal operation, the CPU jumps to the
start address in ROM after the reset switch has been pressed
and then performs the reset program to set up all of the
progr a mmable devices. Following this, the BASIC interpreter
residing in ROM is in control of the CPU.
RAM (Ul4 thru U21) provides storage for the programs and/or
data currently being executed. In the standard unit, these
eight res are 16K x 1 (MCM4517) but may be upgraded to 64K x
1
res (MC6665) as an option (see Paragraph 3.3 for
instructions). In addition, this same RAM is used to
generate the video display. Normally, no conflict will be
observed because the program wil l use one portion of RAM and
the display will use another. Duri ng normal usage, the
BASIC interpreter located in ROM will cont rol the execution
of programs located in RAM.
A central component in the Color Computer 2 is the
Synchronous Address Multiplexer (SAM, U22). This chip
provides refresh and address multiplexing for the RAM. It
also provides all of the system timing and device selection.
The video display generator (VDG, U8) provides virtually the
entire video interface on one chip and allows several
alphanumeric and graphic modes. The mode of operation of
the VDG is controlled by one of two Peripheral Interface
Adapters (PIAs, U2 and U7) used in the Colo r Computer 2.
With this information and RAM data , the VDG generates
composite video and color information for the modulator
circuitry.
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