Radio Shack TRS-80, Color Computer 2 Service Manual

·-

•

erv1ce

TRS-BO

Color

Catalog

Computer

Number

26-3026/7

®

2

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.

----------ltad1elllaell----------

Color

Computer

2

TRS-BO

®

Service

Manual

1/

General

1.1

1.

1.

2/

2.1

2.2

2.3

3/

3.1

3.2

3.3

4/

Introduction

2

System

3

Memory

Specifications

Physical..
Power
Technical.

Disassembly/Assembly

Disassembly

Assembly .....•...........

64K

Theory

Description

Map .

.....

Upgrade

Of

Operation

TABLE

•......

......

.............

.........

Instructions.

OF

CONTENTS

1

.

.

.

1

6

13
13
13

15
16
18

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

MC6809E
Reset

Memory

Video
Artifacting
PIAs

ROM •

Keyboard
DAC

SALT
Cassette

RS232
Cartridge
Power

Joysticks

TV

Schematic
Component
Circuit
Circuit

Parts

Circuit

.......

Generation

....•

•••••

Circuitry

Circuitry

Switch

List,

CPU

...

..
.

............

Interface

.....

.•........•.••.

Tape

Connector

Transformer

......

8000191,

Layout
Trace,
Trace,

Format

Connector

Box

.•.

PCB
PCB

PCB

8857636

Circuitry.

..
.

(J3)

(J6).

.........

.

Color

1700235,

8857636,
8857636,

ltadle

.

Information

.

Computer.

Main

Component
Solder

................

..

Logic

Board

Side

Side

..
.

lhaell----------

8857636.

.......

. • ..

19

26
27
31
34
36
39
39

41

44
48
49
51
55
55
56
57
61

.

63
65
67

i

Color

Computer

-----------TRS-BO

5/

Troubleshooting

5

.1

Introduction

5.

2

Video

5.2.1

5 . 2 . 2 No

5.2.3

5.2.4

5.2.5

5.2.6

5.2.7

5.

3

Keyboard ...........................................

5.3.1

5.3.2

5.

3.

3

5.

4

Processing

5.4.l

5.4.2

5.5

Cassette

5.5.l

5.5.2

5.5.3

5.6

RS

5.6.1

5.6.2

5.7

5.8

5.9

5.10

Sound
Joystick
Cartridge
Power

Problems

No

Display

Sync

"Garbage"

Clear

No

Color .........................................

Wrong

No

Artifacting

No

Keyboard

Some

Keys

Wrong

General

Symptoms

Motor

Write
Read

2 3 2

Problems

Problems .....................................

Output

Input

Problems .....................................

Supply .......................................

2

®

.

......................................

..

...................................

.......................................

..........•..................•..•.......•..

on

Screen

Screen,

Colors .....................................

No

Or

Entry

Inoperative~

Character

Problems ................................

..........................................

.........................................

Problems ..................................

Control

Problems

Problems

..

..

Missing

Problems ...................................

Problems

Problems .................................

..............................

Signon

Improper

..................•••......

Artifacting

..............................•..

...........................

for

Key

Pressed

.........•....•....•........

.................................

..................................

or

Incorrect

..................................

......................

Service

...........

...............•...

Manual

.

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

6/

Exploded

Exploded
Parts

Appendices

MC6809E
SN74LS783
MC6847
MC6821
MC6822

----------

Data

Data
Data
Data

View/Parts

View

List

Sheet

Data

Sheet
Sheet
Sheet

List

.......................................

..........................................

Sheet

(Motorola
(Motorola
(Motorola

(Motorola

(Motorola

DS9846-Rl)

ADI-595)
DS9823)
DS9435-R2)

ADI-938)

llad1elhaell----------

98
99

ii

Color

Computer

-----------TRS-BO

2

®

-----------

Service

Manual

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

LIST

Description
Color

Color
Color
Color
Color
Color
Color

Shield

Power

64K

MC6809E
MC6809E
MC6809E
MC6883

DRAM

DRAM

Color
Color
PIA
Color

DAC

SALT
Color

I/O

RS-232C

Joystick

Antenna

Computer
Computer
Computer
Computer
Computer
Computer
Computer

Clip

Cord

Upgrade.

2

Installation....................

2

Block

2

Memory
Memory

2
2

Memory

2

Memory

2

Memory

Location

Strain

. . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . .

Relief

Programming
Pin

Assignments

Read/Write

Reset

Block

Timing......................................

Circuitry

Diagram

Computer

Computer

Block

Diagram................................

Computer

Block

Block

Diagram................................

Diagram

Computer

Circuitry....................................

Connector

Timing

...............................

2

Address

2

Artifacting

2

Keyboard

...............................

2

Power

Pin-Out

Schematic...............................

Switch

Box

Schematic

OF

FIGURES

Diagram...................

Map
Map
Map
Map

(Page
(Page
(Page
(Page

Map C Page

.............................

.........................

Model

........................

..•.......................

at

0.895

...........................

Decoding

Circuitry

Array

Supply

..................

....................

........•....•..........

.....................

1).

. . . . . . . . . . . . 6

2).............

3).............

4)

.............

5).

. . . . . . . . . . . .

MHz

...........

................

...........

Page

No.

2

4

7

8
10
11

16

17

18

20
23

25
26

28

29

31
35
37
40

42

45

46

47

49

55

56

,..

.·

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

Normal

Power

Defective
High

E

VDG

Y

Phase
Phase

Phase

Frequency

and

Q

Clock

and

Phase

Band
Band
Band

Artifacting

Artifacting

Artifacting
Address

Data

Lines

Clocks.

Lines

----------

Supply.

Power

and

Modulator

B...

Phase

Phase
Phase

Supply

Component

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8

...........................

of

Clock

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A

Relationships,

A

Relationships,

A

Relationships,

Signals..............................

Signals..............................

Signals..............................

(Typical)

(Typical)

..........................

.............................

ltadtelhaell----------

iii

+5V

Source

....................

Green
Blue
Red

...........

Screen

Screen

Screen

...

....

..

88
89

90

90

91

92

92
92
93

93

93
94
94

Color

Computer

-----------TRS-80

2

®

-----------

Service

Manual

Fig.
5-15

5-16
5-17
5-18

6-1

1
2

3

Description

RAS*

Data
Sound

and

IN

and

Cassette
Color

Line

Computer

Printer
Alternate
Cartridge

CAS*

and

Data

Cassette

Zero

Line
Connector

LIST

...................................

variables

OF

OUT

Output

Crossing

2

Exploded

LIST

Printer

FIGURES

........••••.................

.......................

Detector

View

OF

TABLES

...................•.......

Variable

Signals......................

(con't)

.................

...................

Values

.......•...

Page

.

.
.

No.

95
95

96
96

98

51

52

53

--------------------ladtelhaell-------------------

iv

Color

Computer

-----------TRS-BO

1/

General

2

®

Service

Manual

1.1
The

popular

reliable
latest

monitor,
versatility

typical
Interconnecting

control
remember

to

device
The

ROM
program

receptacle

Multipak

be

module

by
peripheral

added
and

Introduction

Color

Color

operation

in

printout
installation
transfer

to

installing

or

Color
which

modules/cartridges

Interface

installed

active

a

switch

to

the

retrieval.

Computer

electronic

the
Computer

is

Computer.

of

the

cables

remove

any
Color

accessed

at

the

at

the

at

on

the

devices,

Color

2

is

as

its

technology.

device,

Color

of

between

all

peripheral

Computer

2

contains

when

right

module

same

any

one

Multipak

such

Computer

a

refined

It

is

predecessor,
or

Computer

the

Color

are

noted

the

power

the
may

side

allows
time
time

Interface

as

an
2

designed

modem

which
major
from
device

2.

an

internal

unit

be

of

the

up

with
selected

external

for

version

Interconnection

provides

2.

Computer

components.

the

to

is

inserted

unit.
to

selection

additional

of

to

provide

but

incorporates

Figure

2.

provide

Color

prevent

BASIC

powered

into

An

four
either

module.

disk

maximum

Computer

program

Radio

to

1-1

shows

signal

Always

damage

program

up.

the

optional

of

the

by

software

Additional
drive,
memory

Shack's
the

same

a

video
a

and

2

prior

to

Other

paks
specific

may

storage

the

the

in

to

or

be

All

must

inputs
exception
the

rear

inputs
connector,
recessed
on

the

1.2
The

by
Random

These

SAM,
RAM,

operate
allow

System

primary

five

five
VDG,
ROM,

communication

be

panel

(right

channel

TV)

40-pin

Access

and
added.

-----------

to

or

of

the

of

and

Power
is

also

Description
functions

Large

Memory

chips

and

two

and

a

provide

outputs
program

the

left),
ON/OFF
switch

located

are

PIAs.

power

a
with

from

module/cartridges,

unit.

Serial

switch,

(for

of

the

Scale

CRAM)

labeled

With

supply,
composite

the

the

Color

These

I/O,
and

selecting

on

the

rear

Color

Integration

and

Read

on

the
only
the

Color

video

outside

Computer

include

Cass

RESET

either
panel

Computer

(LSI)
Only
Block

these

Memory

five

Computer

output.

world,

I/O,

switch.

Diagram

ltadtelhaeli----------

are

the

of

2

chips

I/O

2,

contained

joystick

TV

output

A

channel

the

are

performed

plus

CROM).

as

chips

2

will

However,

interfaces

with

3

unit.

CPU,

plus

or

to

the

on

4

- 1 -

Color c ornputer

COLOR

MONITOR

2

TRS-BO

--------~S~e=r~v~i:c:e_~~~~~

®

-

anual

LEFT JOYSTICK

Figure

1-1.

RIGHT JOYSTICK

Color c ornputer

ltad1e lhaell

- 2 -

Installat'

2

----

ion

__ c_o_1_o_

The
Processor
provide
this

limited

data

r_ c_o_m_p_u_t_e_r_ 2

main

.

or

data.

set

component

Unit

request

In
of

____

of

any

(CPU,

addition,
mathematical

U23).

data

TRS-BO

computer

It

is

and

select

the

CPU

and

®

system

the

the

is

capable

logical

is

function

proper

operations

Service

the

of

address

of

performing

Central

the

on

Manual

CPU

to

for

a

the

ROM
providing
Without
instructions.
start
and
programmable
residing

RAM
data
eight
1

generate
observed

BASIC
of

A

(Ul2

then

(Ul4

res

instructions).

the

display

programs

central
Synchronous
provides
also

+

ROM,

address

performs

thru

currently

res

(MC6665)

interpreter

provides

the

in

are

the
because

component

refresh

Ul3

in

CPU

the

In

in

devices.

ROM

U21)

being

16K

as

video

will

located

Address

all

Extended
with

CPU

normal

ROM

the

is

x 1 (MCM4517)
an

In

the

use

located

and

of

a

pre-defined

would

operation,

after

reset

Following

in

control

provides

executed.

option
addition,
display.

program

another.

in

RAM.

in

the

Multiplexer

address

the

system

Basic)
run

wild

the

reset

program

of

storage

(see

this
Normally,
will use

Duri

in

ROM

Color

multiplexing

has

set
and
the

switch
to

this,
the

CPU.

for

In

the

but

may

Paragraph

same

ng

will

Computer

(SAM,

timing

the

function

of
randomly
CPU

set
the

the

standard

be

RAM
no

conflict

one

portion
normal
cont

rol

2
U22).

for

and

instructions.

execute
jumps
has

up

BASIC

programs

upgraded

3.3
is

usage,

is

This

device

been

all

interpreter

unit,

for

used

the

the

the

to
of

of
execution

of

the
pressed
the

and/or

these

to

64K x

to

will

chip
RAM.
selection.

be

RAM

the

It

and

The

video

entire

alphanumeric

the

VDG
Adapters
With

composite
circuitry.

this

display

video

is

controlled

(PIAs,

information

video

interface
and

graphic
U2
and

----------1tad1elhae

generator

on

by

and

U7)

and

color

(VDG, U8)

one

chip
modes.
one

of

used

RAM

data

information

- 3 -

The
two
in

,

provides

and

allows

mode

Peripheral

the

the

ll

-

of

Color Computer

VDG

for

the

---------

virtually

several

operation

Interface

generates

modulator

the

of

2.

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MC6809E

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us

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CONNECTOR

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U5

DATA

OUT

-

LATCH

DISPLAY

DATA

74LS

273

~

11

DYNAMIC

RAM

MCM4517

U14

-21

(64K

x

8)

MC6665

~

DEVICE

U22

1---

SELECl

SAM

DYNAMIC

-

U10

RAM

CONTROLLER

74LS02

~

74LS138

MC6883

DATA

ADDRESS

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U12

(U13}

SK

OR

16K

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ROM

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Color

Computer

-----------TRS-BO

The

remaining

to

Input/Output
part
operator
provided
output,

of

this

to
to

and

circuitry

enter
allow
RS-232

2

circuitry

(I/0)

information.

joystick

input

in

the

Color

communication.

is

the

keyboard

Other

inputs,

and

output.

®

Computer

The

which

I/O

cassette

Service

2

most

allows

circuits

input

is

devoted

important

the

are

and

Manual

1.3
The

breakdown
Computer
which

locates
0400

The
for
locations
locations

registers
memory
data

direction

direction

to

clearing

location

as

register
an

Memory

first

may

to

next
the

I/O

allow

an

input

input.

locations.

Map

page
of

2.
be

the
05FF.

two

PIAs.

are
are
determines

register

register

register
configuration
bit
one

sets

of

the

One

located

video

pages

In

the

the

2

and

address

or

an

the

the

Memory
large
variable

anywhere

display

of

the
general,
I/O

registers
control

what

If

this
is

addressed.

is

addressed.

is

addressed

writing

below,
output.
bit

as

blocks

in
at

Memory

registers.

is

of

the

an

Map

of

this

in

the

the

even

addressed

bit

is

data

to

the

each

A 1

in

output

(Figure

memory

block

the

memory.

hexidecimal

Map

explain

numbered

and

the

Bit

set

high

If

it

Normally,

only

even

bit

the

during

inputs

of

data

and

1-3)

in

the

is

the

addresses

the

memory

odd

numbered

two

at

the

(logic

is

set

the
initialization

and

numbered

the

PIA

direction

a 0

sets

shows

Color

video

BASIC

addressing

of

the

even

low,

outputs.

numbered

1),
the

data

memory

may

the

the

display

normally

from

memory

control

the

data

By

be

set

bit

as

----------1tad1elhaell----------

- 5 -

Color

Computer

2

-----------TRS-80

®

FF00

C000

A000

4000

2000

1000

0000

HEX
ADDRESS

CARTRIDGE

ROM

t

":;~

t EXPANSION

I

ROM

COLOR COMPUTER

USAGE

16K RAM

Service

Manual

64K

RAM

(ALTERNATE

OPERATING MODE)

0600

ANORMAL

VIDEO

0400 I

DISPLAY

Figure

1-3.

Color

Computer

Memory Map

(page

1)

----------1tad1e/haell----------

- 6 -

Color

Computer

2

Service

Manual

-----------TRS-BO

®

-----------

FF00 - FF03

PIA U7

BIT

0 =

KEYBOARD

ROW 1 and

right joystick switch

BIT 1 =KEYBOARD

ROW 2 and

left

joystick switch

BIT 2 =KEYBOARD

ROW

3

FF00

BIT 3 =KEYBOARD

ROW

4

BIT 4 =KEYBOARD

ROW

5

BIT 5 =KEYBOARD

ROW

6

BIT 6 =KEYBOARD

ROW

7

BIT 7 =JOYSTICK

COMPARISON INPUT

Control

of

the Horizontal

0=1RO*to

CPU

Disabled

1=1RQ*

to

CPU

Enabled

sync clock (63.5 microseconds)

0=Flag

set

on

the falling

edge

of

HS

Interrupt Input

BIT 2 =Normally

1:

BIT3=SEL1

:

1=Flag

set

on the rising

edge

of

HS

0=Changes

F F00

to

the data direction register

LSB

of

the

two

analog

MUX

select lines

FF01

BIT

4 = 1 Always

BIT

5 = 1 Always

FF02

FF03

BIT

6 Not

Used

BIT

7 = Horizontal sync interrupt flag

BIT

0=

KEYBOARD

COLUMN 1

BIT

1=

KEYBOARD

COLUMN 2

BIT

2=

KEYBOARD

COLUMN 3

BIT

3=

KEYBOARD

COLUMN 4

BIT

4=

KEYBOARD

COLUMN 5

BIT

5=

KEYBOARD

COLUMN 6

BIT 6=

KEYBOARD

COLUMN

7/RAM

SIZE OUTPUT

BIT

7=

KEYBOARD

COLUMN 8

BIT

0 l .

Control

of

the field sync clock

BIT

1

16.667

Ms

Interrupt Input

l

0=1

RO*

to

CPU

Disabled

1=1RQ*

to

CPU

Enabled

0=

sets

flag on falling

edge

FS

1 =

sets

flag on rising

edge

FS

BIT 2 =

NORMALLY

1:

BIT3=SEL2

:

0=

changes

F F02

to

the data direction register

MSB

of

the

two

analog

MUX

select lines

BIT

4 = 1 Always

BIT

5 = 1 Always

BIT

6

Not

Used

BIT

7 = Field sync interrupt flag

Figure

1-3.

Color

Computer

Memory

Map

(page

2)

-----------

llad1elhaell----------

- 7 -

Color

Computer

-----------TRS-BO

2

®

Service

Manual

FF20 - FF23

FF20

FF21

FF22

PIA

BIT

0 =CASSETTE

BIT

1 = RS-232

BIT

2 = 6

BIT
BIT3=6BITD
BIT

4 = 6

BIT
BIT

5 = 6

BIT
BIT6=6BITD
BIT

7 = 6

BIT

BIT

0 l

Control

BIT

BIT 2 =Norm
BIT
BIT4
BIT
BIT
BIT 7 =

BIT
BIT
BIT
BIT
BIT
BIT
BIT
BIT

RS-232 status

1

3 =

Cassette

= 1 Always
5 = 1 Always
6 Not

0 = RS-232

1 = SINGLE

2 = RAM SIZE INPUT
3 = VDG CONTROL OUTPUT
4 = VDG CONTROL OUTPUT
5 = VDG CONTROL OUTPUT
6 = VDG CONTROL OUTPUT
7 = VDG CONTROL OUTPUT

CD

Used

Interrupt

DATA

DATA

OUTPUT

D/A

LSB

/A

D/A

DIA

/A

D/A

MSB

of

the

CD

Input

ally 1: 0 =changes

Motor

Control : 0

Flag

DATA

INPUT

BIT

SOUND OUTPUT

U2

INPUT

FF20to

=OFF

0 = FI RO*

1 =

0

=set

l

1 =

the data direction register

1

=ON

HIGH=

to

FIRO*to

flag

on

set

flag on rising

16K

CPU

Disabled

CPU

Enabled

falling

edge

CHANGEABLE=

css

GM0 & I
GM1
GM2

A/G

NT /EXT

edge

CD

CD

64K

BIT

01

BIT

1 Interrupt Input

BIT 2 =Normall

FF23

FF40-

FFBF NOT USED

Figure

BIT

3 = Six

BIT

4 = 1 Always

BIT

5 = 1 Always

BIT

6 =

BIT

7 = Cartridge

1-3.

----------1tad1e

Control

BIT

Not

Color

of

the Cartri

y 1: 0 =chan

Sound Enable

Used

Interrupt

dge

Flag

Computer

- 8 -

0 =

FIRQ*

to

1 =

FIRO*

to

0 =sets flag on falling

l

1 =

sets

flag on rising

ges

FF22

to

the data direction register

Memory Map

(page

lhaell----------

CPU
CPU

Disabled

Enabled

edge

edge

3)

CART*

CART

*

Color

Computer

-----------TRS·BO

The

addresses

for

the

SAM

address
data
used

to

and

set

mode.

control

VDG

lines

to

an

even

writing

the

chip

to

control

numbered

register.

To

select

registers

must

any

2

from
the

each
data

all

FFCO

multiplexer

SAM

register.

memory

to

Addresses

a

certain

(V0-V2)

be

set

to

chip;

an

FFDF

therefore,

location
odd

display

and

to

the

®

are

numbered

FFC0-FFC5

the

the

chip
In

general,

will

mode,

PIA

proper

control

(U22).

two

clear

memory

control

the

(U2)

mode.

Service

registers

There

addresses

writing

the
location
the

display

controlling

Manual

are

no

are

any

register

display

mode

the

data

will

Addresses

If

all

at

0000.
display
allows
Register
Color
times.

Addresses

The
Therefore,

Addresses

SAM
Color
only
may

FFDE

cleared,
with

this
of)

available

this
must

Computer

Color

chip.

Computer

by

erase

to
the

bit

the

bit.
not

FFC6

of

the
Normally,

to

the

Pl

FFD6
Computer

FFDA

the

the

FFDF,

the

lower

is

map

for

return

to

registers

start
display

controls

2.

to

registers

to

These

2.

reset

contents
controls

ROMs

32K
set,
and

all

RAM.

The

control

to

FFD3

at

FFD9

FFDD

addresses

routine

occupy

the

control

register

0400.

to

be

a

feature

Therefore,

control

2

is

RO

control

This

of
the

of

address

ROMs
64K
Caution

program

ROM

for

are

cleared,

F2

This

paged

designed
and

Rl

select

memory

in

BASIC.

RAM.

map

the

upper

"disappear"

(less

must

obvious

the

will

feature

through

which

is

should

the

to

should
the

16K

size

Register

type.

space

the

be

must

display

the
be

is

clock

operate

be

memory

or

option

Changes

If

32K

available

from

top

256)

exercised

be

reasons.

display
set
of

all

not
be

speed

cleared.

64K

TY,

this

of

the

in

low

starting

causing

the

SAM

of

the

used

cleared

of

at

0.89

size

setup

of

should

at
at

bit

Memory Map

for

(are

locations

in

memory

address.

will

in

RAM

other
addresses

switched

setting

the

chip

RAM.

the

at

the

MHz.

of

in

be

changed

is
RAM.

are
and

begin

all

CPU.

times

the

the

If

out

The

final

the

interrupt

a

reset
indicated
This

mapped

instance,
contents

dual

or

into

of

series

and

interrupt,
location
set

of

the

if

the

BFFF.

top

----------nad1e111aell----------

of

addresses

reset

it

and

begin

addresses

of

the

CPU

reads

vectors.

will

execution
is
BASIC
FFFF

- 9 -

in

the

load

listed

ROM

it

Color

Whenever

the

address

at

because

(BFF2-BFFF).

will

actually

Computer
the

CPU
at

the

new

the

2

receives
the
location.

vectors

For

read

are

are

the

FFDF
FFDE
FFDD
FFDC
FFDB

FFDA
FFD9
FFD8

FFD7
FFD6

FFD5
FFD4
FFD3

FFD2
FFDl

FFD0
FFCF

FFCE
FFCD
FFCC

FFCB
FFCA
FFC9
FFC8
FFC7
FFC6

FFC5
FFC4
FFC3
FFC2
FF

Cl

FFC0

---

Color

Computer

--------T

s

c TYPE

s

c

s

c

s

c

s

c

s

c

TY

M1

M0

Rl

R0

Pl

s F6

c

s

c

s

c OFFSET

s

c

s

c

s

c

s

c

s

c

s

c

s

c

F5

F4

F3

F2

Fl

F0

V2

Vl

V0

2

MAP

MEMORY

SIZE

CPU

RATE

PAGE

#1

DISPLAY

(BINARY)

DISPLAY
MODE
CONTROL

RS-80

(=0)

(=

0)

'I

I

Address
Display Element

N.

U.-

®

-----------

NU

..

-

~32/64K

_

16K

-4K

1

, I

0 0

1

of

1

·0

Upper-Left-Most

- RG6,

0

= 0000 + (%K Offset)

CG6

-RG3

-CG3

I

1 1

1

1

1

1

0

1

0

0

0

1

}

-N.U

1 1

1

-RG2

0

1

1

Service

Dynamic R

.

_N.U.

-0

0 0

1

0

..

-

CG2

I

0

0

1

0

0 1

A

Ms

.9/1

.8 MHz

0.9 MHz

I

0

RGl

C~

,

Al,

0

0

0

Manual

only

AE,

S4

~

Transparent

Refresh

Figure

----

------

1-3.

Color

Computer

ltadte

-

Memory

Map

(page

lhaell----------

10

-

4)

Color

Computer

2

-----------TRS-80

®

FFFF

OR

BFFF

RESET VECTOR LSB

FFFE

OR

BFFE

RESET

VECTOR

MSB

FFFD

OR

BFFD

NMI

VECTOR

LSB

FFFC

OR BFFC

NMI

VECTOR

MSB
FFFB OR BFFB SWl1 VECTOR LSB
FFFA

OR

BFFA

SWI

1 VECTOR MSB

FFF9

OR

BFF9

I RO VECTOR LSB

FFF8

OR

BFF8

IRO

VECTOR MSB

FFF7

OR

BFF7

FIRO

VECTOR

LSB

FFF6

OR

BFF6

Fl

RO

VECTOR

MSB

FFF5

OR

BFF5

SWl2

VECTOR

LSB

FFF4

OR

BFF4

SWl2

VECTOR

MSB

FFF3

OR BFF3

SWl3

VECTOR

LSB

FFF2

OR BFF2

SWl3

VECTOR

MSB
FFF1 OR BFF1 RESERVED
FFFO OR BFFO RESERVED
FFEF -

FFEIJ

NOT

USED

Service

Manual

Figure

1-3.

Color

Computer

Memory Map

(page

5)

----------1tad1elhaell----------

-

11

-

Color

Computer

-----------TRS·BO

2

®

-----------

Service

Manual

--------------------nad1elhaell---------------

-

12

-

Color

Computer

-----------TRS-80

2/

Specifications

2

®

Service

Manual

2.1

2.2

2.3

Physical

Size:

1.

2.

Weight:

Power:

Technical

1.

Microprocessor:

2.

Memory:

Width

Depth
Height

4.75

110

vac

RAM:
ROM:

-

-

lbs

14.

10.35"
3 •

-

(2.15

60

75"
55

Hz,

(37.5
(

26.

II

(9.0

kg)

0.2

Type -Motorola
Clock

16K

Expandable

BK

Standard

BK

Extended

total

Up

to

cartridge)

cm)
cm)

3

cm)

Amps

Speed

of

16K

additional

RMS

-

Basic

Basic

16K

typical

MC6B09E

O.B96

to

64K

(26-3026

(26-3027

Basic

MHz

ROM

ROM

)
) ,

(in

3.

4.

5.

6.

7.

Keyboard:

Video:

Sound:

cassette:
RS232C:

Sources:

53-key

matrix

RF

Modulated

or

4

characters

32

Up

to

Graphic

192

Six-bit
Single
Input

Input

1500

3-wire

Baud

control

microprocessor

output,

by

B

colors
resolution

pixels

DAC

bit
from
from

cassette
cartridge

Frequency

interface

16

rows

up

recorde

Shift

under

scanned

channel

to

256

r

connector

Keying

software

3

x

-----------

llad1e/haell----------

-

13

-

Color

Computer

2

Service

Manual

-----------TRS-80

®

-----------

2.3

Technical

Ccon't)

8.

Joystick:

9.

Expansion:

2

connectors,

2

axes

each,

DC

voltage

input

of

0.25

to

4.75

volts

in

64

steps

40-pin

cartridge

connector

con-

taining

all

major

CPU

signals

necessary

for

interface.

----------

lladtelhaell----------

-

14

-

Color

Computer

-----------TRS-BO

3/

Disassembly/Assembly

2

®

Service

Manual

3.1
Disassembly

using
pliers.

housing

disassemble

1.

2.

3.

4.

5.

Disassembly

only

are

Disconnect
unit.

Remove
Turn

to

prevent

Loosen

the
come

Turn
cover
care
keyboard

of

the

a

Phillips

Mounting

accessible

the

cartridge

the

unit

and

base

out

the

from

to

to
until

unit

prevent

assembly

Color

screwdriver

screws
computer,
power

damage
remove

the

the

and

from

over

top

the

rightside

bottom

damage

Computer

for

from

follow
remove

slot

and

to

the

the

six

cover.

unit

cover

and

printed

attaching

the

underside

the
signal

(if

place

keyboard

mounting

These

is

turned

up.

and

to

the

2

is

easily

and

a

pair

the

steps

cables

applicable).

it

on a soft

or

screws
screws
over.

Carefully

set
flat
circuit

cable

two

of

noted

top

it

board.

accomplished

of

long-nose

halves

the

unit.
below.

from

surface

cover.

which

may

lift
aside.

not

the

between

of

the

To

the

attach

easily

top

Exercise

the

6.

7.

8.

9.

Disconnect
the

keyboard.

Tag

the

the

left
printed
of

long-nose

Remove

case

from

attach

Remove

two
assembly
rating

three

cover.

the

it
the

attaching

fuse.

from

three

rear

circuit

PCB,

to

transformer

should

the

wires

of

the

board.

pliers.
screws

If

it

do

so

the

PCB.

screws.

be

PCB

the

cable

from

which

is

by

accomplished

the

unit

which

Remove

attach

necessary

removing

from

Replacement

the

which

transformer

are

attached

the

wires

the

to

remove

the

eight

unit

of

using

is

PCB

by

removing
the
the

assembly
using

to

-----------1tad1elhaeli-----------

attached

to

the

the

shield

clips

pigtail

same

at

the

a

pair

bottom

which

the

fuse

type

to

and

-

15

-

Color

Computer

-----------TRS-BO

2

®

-----------

Service

Manual

3.2

Assembly

Assemble

disassembly.

metal

There
the
proper

clips.

are

keyboard.

RFI

the

Color

three

shielding.

The
Five

clips

These

Computer

PCB

shield

clips

which

shields

See

2

is

ground

provide

must

Figure

RFI

in

the

reverse

attached

the

shield

RFI

be

in

3-1

SHIELD CLIPS

for

to

to

shield

place

clip

order

the

the
to

of

PCB

with

PCB.

ground

provide

location.

for

RFI

SHIELD

CLIP

When

ensure
plastic

will

reattaching

that

shield

prevent

reconnecting

of

screws

case

parts.

are

Figure

the

between

any

the

used

Ensure

the

wires

damage
top

to

3-1.

wires

are

and

mount

that

Shield

installed

the

to

bottom
the

Clip

from

the

transformer
the

wires

covers.

the

PCB

correct

Location

transformer
in

the

slots

and

the

or

insulation

Two

and

the

type

is

to

PCB.

different

top

and

used

the

of

when

when

PCB,

the

This

types

bottom

reassembling.

The

strain

around

that
relief

the

the

power

to

relief

plastic

the

on

the

bosses

cord

is

transformer

power

at

properly

connections

the

cord

rear

routed

consists

of

the

to

(see

of

unit.

afford

Figure

a

wrap

strain

3-2).

Ensure

-------------------nad1elhaell------------

-

16

-

Color

Computer

-----------TRS·BO

MOUNTING

SCREWS

(2) FUSE

2

®

-----------

Service

Manual

Figure

E2

/

3-2.

a_----

Power

TRANSFORMER

PLASTIC SHIELD

ON BASE

Cord

Strain

Relief

TOP

VIEW

----------lladlOlllaell----------

-

17

-

__

c_o_1_o_r_c_o_m_p_u_t_e_r_2

____

TRS-BO

®

Service

Manual

3.3
To

following

1.

2.

3.

4.

64K

upgrade

Disassemble

access

eight
Install

8040665
in
noted

Solder
schematic,

Run

operation
in

Upgrade

a

procedure

to

ICs

Ul4

through

with

a

app~opriate

the

reverse

16K

the
from

the

--

total
notch

jumper

LH

of

Instructions
Memory

must

the

RAM

the

64K x 1

U21.

side,

the

order

Unit

be

unit

wire

diagnostic

res,

PCB.

of
in

new

as

ICs
8

ICs)

Ensure

the

at

above

memory
of

to

a 64K Memory

followed:

noted

Ul4

CMC6665,

proper

terminal

disassembly.

in

through

in

place

that

U2).

program

chips.

Paragraph

U21.

Radio

of

chips

location.

Wl

(see

to

Assemble

Unit,

Remove

Shack
the
are

Sheet

verify

the

3.1

to

these

Part

ones

installed

removed

2

proper
the

allow

No.

as

of

unit

00

C3 2 !
C4

(.) (.)

Qo

U14

~

cso -c::>-

U15

~

-c:J-

C51

C52

-c::>-

Figure

~I

U9

-g-~

U20

U17

U18

c:::Jcsg

16

U19

~ ~ ~ ~

C53

-c:J-

Replace

3-3.

these

64K

chips

Upgrade

I

..

Cl

....

..

a:

U21

~~~

-t::>-

C57

-----------

llad1elhaell----------

-

18

-

Color

Computer

2

Service

Manual

-----------TRS-BO

®

-----------

4/

Theory

Of

Operation

4.1

MC6809E

CPU

(U23)

The

heart

of

any

computer

system

is

the

Central

Processing

Unit,

or

CPU.

In

the

Color

Computer

2,

as

well

as

most

modern

microcomputers,

the

CPU

is

a

single

Large

Scale

Integrated

Circuit

(LSI).

The

CPU

gathers

instructions

and

data

from

memory,

interprets

and

executes

the

instructions,

and

stores

the

results

of

the

data

operations

into

memory.

Additionally,

the

CPU

stores

data

to

and

retrieves

data

from

various

input/output

CI/0)

devices.

The

Motorola

MC6809E

Microprocessor

is

perhaps

the

most

powerful

8-bit

microprocessor

available

today.

There

are

several

ways

to

determine

the

"size"

of

a

microprocessor

<whether

it

is

8-bit,

16-bit,

32-bit,

or

whatever).

One

way

involves

the

number

of

data

interconnecting

lines

the

processor

possesses.

Another

is

the

size

of

the

internal

registers

and

the

size

of

the

mathematical

and

logical

operations

supported

by

the

processor.

Although

the

MC6809E

has

an

8-bit

data

bus,

internally

it

contains

four

16-bit

registers

and

two

additional

8-bit

registers

which

may

be

linked

together

to

form

another

16-bit

register.

The

MC6809E

also

supports

some

16-bit

mathematical

and

logical

operations.

Therefore,

although

it

is

technically

an

8-bit

processor,

it

has

some

of

the

power

of

the

16-bit

machines.

Figure

4-1

is

a

"programmer's

model"

of

the

MC6809E CPU.

Following

is

a

brief

description

of

the

registers

and

their

respective

functions.

Additional

information

may

be

obtained

from

the

MC6809E

data

sheet.

The

Program

Counter

CPC)

register

is

a

16-bit

register.

It

is

the

job

of

the

program

counter

to

keep

track

of

which

instruction

is

next.

Instructions

for

the

MC6809E

processor

are

from

one

to

five

bytes

in

length.

As

each

instruction

is

fetched,

its

specific

bit

pattern

allows

internal

logic

in

the

CPU

to

determine

the

length

for

that

instruction.

'!'he

PC

is

then

immediately

updated,

even

before

the

remainder

of

a

multi-byte

instruction

is

executed.

The

Hardware

Stack

Pointer

(S)

is

another

16-bit

register.

Its

job

is

to

"point"

to

a

specific

area

of

memory

that

is

set

aside

by

the

systems

programmer

for

the

specific

use

of

the

CPU.

From

time

to

time,

the

CPU

finds

it

necessary

to

"remember"

more

than

it

has

internal

capacity

to

store.

In

these

cases,

it

"pushes

the

data

onto

the

stack".

Later,

when

----------llad1elhaell----------

-

19

-

Color

Computer

-----------TRS·BO

2

®

-----------

Service

Manual

15

___

A____,l_I

0

PC

s

- PROGRAM COUNTER

- HARDWARE STACK POINTER

u - USER STACK POINTER

x

y

B-------'

- INDEX REGISTER

- INDEX REGISTER

- ACCUMULATORS

-----------

D

DP

CC - CONDITION CODE REGISTER

Figure

- DIRECT PAGE REGISTER

4-1.

MC6809E

Programming

llad1elllaell----------

Model

-

20

-

__

c_o_1_o_r_c_o_m_p_u_t_e_r_2

it

is

ready
from
execution
has
next
instruction
after
to
storing
altering
program

(RTS)

the

already

instruction.

the

return

instruction.

to

stack".

of

updated
will

execution

to

the

return

of

the

flow

____

retrieve

One

a

subroutine.

alter

the

next

PC,

upon

encountering

example

itself

The

Branch
the

of

the

instruction

address

the

TRS-BO

the

information,

of

Recall

to

contain

to
contents
subroutine,

on

the

CPU

is

®

the

that

Subroutine

of

following
stack

able

the

to

Return

use

the

it
of

the

address

the
the

prior

return

from

Service

"pulls
the
program

(BSR)
PC.
CPU

is

the

to
to

Subroutine

Manual

the

data

stack

However,
BSR. By

the
the

is

counter

of

the

required

main

the

The
temporary

Pointer
as
programmer,
hardware-related

Two
registers.
points
much
beginning
book.
table

The
B.
CPU,
mathematical
MC6809E,
double

S

register

instructions.

called

the

S

additional

in

the

Data

by

MC6809E

The

accumulators

and

(D)

storage

as

memory,

same

of

reference

are
the

accumulator,

is

also
of

In

addition,

the

far

as

but

is

storage

16-bit

These

way a book

the

can

CPU

the

and

two

registers
such

Logarithmic

then

(U23)

registers
logical

accumulators

data

U

register.
the
not

registers

be
to

the

contains

are

available

via

the

there

pushing
used

as

which

by

requirements.

can

the

beginning

mark

retrieved

the

operations

can

Tables

pointer

main

upon

can
is

to

Push
is

This
and
the

are

be

mark

from
used.

two

workhorse

which

be

then

the

and

a

dedicated

register
pulling
CPU

for

the

used

the

in

the

(or

8-bit

most

are

combined

a

programmer

Pull

acts

of

data

any

of

X

and

Y

index

to

mark

of

a
page
back
stored

accumulators,

of

performed.
16-bit

specific

data

that
of

registers

the
to

register.

for

user

the
by

its

table,

a

into)

form

Stack
the

is

math

of

In

one

same

the

the

A

and
a

the

----------llad1elhaell----------

-

21

-

Color

Computer

-----------TRS-80

2

®

Service

Manual

Another
When
significant
DP

register.

The
individual
individual
processor
programmer
conditions.

8-bit

memory

Condition

C -

V -

Z -

register

is

accessed

eight

Code
bits,
bits

operations.

to

the
an
register

the

set
of
notation.

the
an

rather

are

mask

The

bits

carry

operation

overflow

when

the

register

zero

operation

bits

Register

set

out

are:

bit.

to

store

the

bit.

is

the

in

of

the

than

or
The
two

This

is

greater

bit.
result

to

This

is

equal

Direct

the

Direct

address

CCC)

an
cleared
other
of

the

bit

it.

Similar

is

store

bit

is

8-bit

as

two

three

is

than

greater

it

is

to

zero.

Page

Mode,
will

best

group.
the

bits

set

to

in

set

(DP)

be

thought

result

are

possible

when

the

capacity

the

than

"two's

when

register.

the

most

taken

Six
used

the

C

bit,
the

complement"

the

from

of

as

of

these

of

internal

by

the

interrupt

result

of

but

capacity

result

the

eight

of

the

it

of

is

N -

I -

H -

F -

E -

the

negative

the

most

operation

the

IRQ

mask
programmer
interrupts.

the

half-carry

processor
the

FIRQ

it

is

desired

the

"Entire"
interrupts,
preserved.
indicating

bit.

significant

is

set.
bit.

when

in

mask

that

it

bit.

decimal

bit.

to

flag.
indicating
It

is

only

The

bit

The

is

This
arithmetic

Is

ignore

This

cleared

PC

negative

(sign

IRQ

desired

bit

set

FIRQ

bit

that

by

and

bit)

mask

to

is

by

the

interrupts.
is

all

FIRQ

CC

were

bit

is

set

of

an

bit

is

set

ignore

used

operations.

set
registers

by

programmer

by

NMI

interrupts,

preserved.

IRQ

the

were

when

by

the

when

and

IRQ

----------

nat11elhaell----------

- 22 -

Color

Computer

2

-----------TRS-80

®

Service

Manual

Figure

4-2

shows

the

pinouts

of

U23,

the

MC6809E CPU.

Note

that

there

are

sixteen

address

lines

(AO

through

Al5).

These

address

lines

are

output

from

the

CPU

and

are

used

to

select

one

of

65,536

different

memory

locations.

The

memory

and

I/O

devices

must

be

wired

to

accept

the

correct

combination

of

highs

and

lows

on

the

address

lines.

The

order

of

the

devices

and

how

they

respond

to

the

different

lines

is

called

the

memory

map.

PIN

ASSIGNMENTS

V

ss

1 e

-1

0

HALT

NMI

2

39

TSe

TRO

3

38

Lie

FiRO

4

37

RTI"Ei

BS

5

36

AVMA

BA

6

Vee

7

AO

8

33 BUSY

A1

9

32

R/W

A2

10

A3

11

30

01

A4

12

29

02

A5

13

28

03

A6

14

'L

l

04

A7

15

26

05

AB

16

25

06

A9

17

24

07

A10

18

23

A15

A11

19

22

A14

A12

20

Figure

4-2.

MC6809E

Pin

Assignments

----------llad1elhaell----------

-

23

-

Color

Computer

-----------TRS-BO

The

CPU

has

eight
bidirectional
data

The

functions,
course,
the
signal.
These

In

SAM

0.89

signal
The

specific
Computer

to

and

remaining

the

GND

line

clock

the

Color

chip

MHz.

which

CPU

contains

retrieve

both

Vee

The E and

signals

and

As

sequences

2

are:

2

data

and

are

lines

input

pin

is

the

Q

Computer

are

50%

shown

leads

E

a

number
of

lines

used

data

on

the

control

is

the

return

lines

must

2,

duty

in

Figure

by

events.

by

from

CPU
power

reference

are
be
these

cycle

90

degrees.

of

(D0-D7).

the

memory

are

and

the

present

signals

clocks

4-3,

inputs

The

®

-----------

processor

or

used

output

input

for

clock

for

Q

is

which

ones

These

I/O

for

control.

line

both
inputs

the

are

provided

at

a

a

quadrature

serve

used

Service

data

to

lines

both

devices.

control

to

the

power

to

CPU

to

frequency

to

by

the

Manual

are

route

Of
CPU

and

and

the

CPU.

function.

by

the

of

clock

initiate

Color

RESET* ­HALT*

NMI*

IRQ* -

FIRQ* -

Upon

<if

receipt

enabled),
address
1 -

System

registers
receipt

-

-

of

from

the

Description).

are

of

the

Used
Stops

of

on

the

current

power

continue
Non-Maskable

CPU

to

"interrupt"

and

execute

routine.

Interrupt
masked
CC

register.

Fast
masked
doesn't
other

the

the

CPU

(defeated)

Interrupt

by

preserve

interrupts).

RESET

will

Vector

preserved

RTI

(Return

up

program

instruction.

after

Interrupt.

a

special

Request.

the

F

signal,

get

Table

For

on

the

from

and

flow

HALT

is

its

Similar

by

Request.

bit.

all

or

the

appropriate

(see

the

the

interrupt

Stack

Interrupt)

to

reinitialize

after

Execution

removed.

Always

normal

"Interrupt

setting

Similar

It

is

registers

any

of

map

to

be

the

completion

will

causes

program

Handler"

to

NMI

but

the

I

bit

to

faster

the

because

(as

do

interrupts

subroutine

in

the

Section

routines,
restored
instruction.

the

flow

may

IRQ,

the

upon

the

in

CPU.

be

the

but

it

-----------llad1elhaell-----------

-

24

-

Color

Computer

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2

Service

Manua

l

®

111

7ns

629n

2.

4V

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s

o.sv

s

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Figure

4-3.

----------1tad1elhaell----------

NOTVALID

MC6809E

WRITE

DATA

TIMING

Read/Write

-

25

-

Timing

at

0.895

MHz

Color

Computer

------------TRS-80

2

®

-----------

Service

Manual

Other

(Three-state
TSC
DMA
go
Computer
permanently
CPU
data
read).
Figure
is
presented
presents
fast.

4.2

The
CRll,
different
provide
used
also
output
circuitry.

control

line
environment

into

modified

a

to

inform

transfer

Standard

4-4.

Reset

reset

and

a

to

used

signal

reset

lines

Control)

is

an

input

three-state

2

does

grounded.

the

is

However,

by

the

to

the

no

problem

Circuit

circuit
CR12.

time

pulse

as

durations

the

an

from

used

and

intended

and

will

condition

not

require

external

from

MC6809E

memory

This
of
output,

the
in

SAM

as

is

comprised

circuit

approximately

SAM

chip

pin

in

the

the

cause

multiprocessing,

The

R/W

memory

CPU

Read/Write

the

chip
long

7

only

for

so

of

so
as

(U22).

diode

U22

Color

R/W

Color
during

provides

power-up

(Read/Write)

for

use

the

if

line

and

(a

write)

that
the

of

R20,

10
CRlO

from

Address
high.

memory

Computer

in

a

Since

is

an

output

devices

or

timing

Computer

the

addresses

the

active

is

R22,

pulses

or

reset.

milliseconds

The

reset

is

used

the

rest

2

are

TSC

line.
multiprocessor
and

Data

the

this

whether

to

the

is

shown

2,

this

E

sufficiently

C48,

of

input

to

of

lines
Color

line

used

CPU

in

timing

are

time.

C58,
two
R22

which

to

isolate

the

and

reset

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is

by

the

the

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This

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C58

is

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the

or

to

is

+

sv

R22

100

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SWITCH

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i_y

-

-

Figure

CR12

CR11

C58

I 0.1µF

-

- -

VCLK SAM CLK VDG

4-4.

MC6883

CR10

3.58 mHz

U22

MC6883

Reset

----------llad1elhaell----------

us

MC6847

Circuitry

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R20

100

C48

11.0µF

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Kn

U23

MC6809E

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c_o_1o_r_c_o_m_p_u_t_e_r_2

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second
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and
milliseconds.
CR12
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discharge

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is

R20

becomes

and

reset

provided

provide

capacitors
slowly

R22).

____

pulse
to

this

CRll

forward

through

is

the

master

is

used

biased

C48

TRS-BO

the

master

CPU

and

reset
to

upon

and

C58,

their

®

both

pulse

isolate

power

rather

normal

system
PIA's

of
the
down

than

charging

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reset

CU2
approximately
two

and

signal.

and
R/C

is

them

resistors

U7).

circuits.
used
having

Manual

C48
100

to

to

4.3
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(DRAMs,

storing

at

bits

array

Computer
In

lines

16

called
row
this
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addresses
presented,
cycle,
retrieved
output
access
WE
time.

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any

at

is

order

are

pins,

address

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the

signal

Computer

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16,384

given

a

time,
said
2

operate

to

required.
the

row

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and

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from

pin

time

are

Figure

thru

bits

time.

to

address

addresses

address

is

presented
row
the

has

row

along

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the

some

of

the

active
4-6

2

U21).

(16K),

Since

eight

be

16K x 8.

from

16K

and

address
absence

latched

addresses),

with

Enable)

appropriate

time

DRAM.

shows

uses

However,

later.

prior

Dynamic

Each

the

DRAMs

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single

locations

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column

first,

by

of

CAS*.

is

During

the

any

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the

CAS*

the

to

memory

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CPU

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since
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and

presence
least

the

If

the

held

cell

The

CAS

read

Random

chip

of

needs
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+5

volt

in

each

the

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significant

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and

write

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access

in

the

supply.

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addresses

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two

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the

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data

memory

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only

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memories.)

you

memory

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MC6883

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to

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Video

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RF

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Manual

4.5

Artifacting

The

Motorola

MC6847/MC1372

component

combination

is

designed

to

produce

several

modes

of

graphics

operation.

The

highest

resolution

mode

(192

by

256

pixels)

is

designed

to

be

a

black

and

white

mode.

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this

mode,

the

MC6847/MC1372

component

combination

does

not

produce

the

color

burst

signal

necessary

to

make

the

television

"see"

color.

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is

a

phenomenon

whereby

a

color

television

set

can

reproduce

color

from

essentially

a

black

and

white

signal,

if

the

period

of

the

signal

is

less

than

that

of

the

color

oscillator

signal.

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for

the

television

set

to

do

this,

it

must

receive

the

color

burst

signal.

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artifacting

circuit

in

the

Color

Computer

2

forces

the

Motorola

MC1372

(09)

to

generate

the

burst

signal

in

the

high

resolution

mode,

contrary

to

the

original

design

of

the

component.

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addition,

the

phase

of

burst

generated

is

controlled

to

a

limited

degree

in

order

to

produce

a

desired

set

of

hues,

or

tints,

from

the

black

and

white

signal

which

is

now

being

interpreted

as

color.

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Color

Burst

signal

is

approximately

eight

cycles

of

3.58

MHz

riding

on

the

back

porch

of

the

horizontal

sync

pedestal.

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the

television,

this

signal

is

used

to

synchronize

the

set's

internal

chroma

oscillator

in

both

frequency

and

phase

to

the

transmitted

signal,

so

that

the

proper

colors

are

demodulated.

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phase

of

the

chroma

signals

with

reference

to

this

signal

determines

the

tints

of

the

colors

on

the

screen.

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the

absence

of

this

burst

signal

triggers

a

"color

killer"

circuit

in

the

TV

set,

which

shuts

off

the

chroma

bandpass

amplifiers

in

the

set.

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purpose

of

this

is

so

that

old

black

and

white

programs

will

be

seen

without

colored

"snow",

which

is

random

noise

amplified

by

the

chroma

bandpass

amplifiers.

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no

burst

received

by

the

TV,

the

color

killer

should

insure

that

the

set

produces

a

black

and

white

picture.

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colors

produced

in

the

artifacting

mode

depend

upon

the

phase

of

the

signal

that

is

being

interpreted

by

the

TV

as

burst.

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is

possible

to

force

the

MC6847

(08)

into

one

of

the

color

modes

during

horizontal

sync

time

and

thereby

cause

it

to

send

the

signal

to

the

MC1372

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makes

it

generate

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the

correct

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display

is

active.

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if

this

approach

is

used,

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burst

generated

by

the

MC1372

will

cause

the

TV

to

reproduce

the

"free

colors"

as

magenta

and

green,

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N/C

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Halt

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to

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1

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14

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4

15

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5

16

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6

17

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7

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20

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21

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2

22

A3

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23

A4

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4

24

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5

25

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26

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27

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8

28

A9

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9

29

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10

30

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1

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11

31

A12

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12

32

CTS*

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33 GND

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34

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35

SND

Sound

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36

scs*

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A13

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13

38 A14

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14

39

A15

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Bit

15

40

SLENB*

Input

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Table

3.

Cartridge

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Joysticks

optional
assemblies
a

schematic

a

push

button

potentiometers

is

a

both

reads

regardless
This
be

This

used

signal

allows

Transformer

Computer
transforms
supply.

is

3/10

amp,
should
parts.

Joystick

which

of

the

switch

connected

second

from

disables

by

the

2

Power
it

The

1.8
slow-blowing

only

Controllers

can

plug

Joystick

for

chip

of

and

select

writes

the

map

the

decoded

but

cartridge

Transformer

to

17.2

current

amps

be

replaced

into

RMS

Jl

VAC

rating

maximum.

Assembly.

the

fire

by a mechanical

signal

to

addresses

type.

internal

unused

hardware.

accepts

center-tapped

of

the

fuse.

with

are
and

The
genuine

two

J2.

It

button

and
assembly.

from

device

sections

110

secondary

The

primary

fuse

identical

Figure

consists

the

Ull.

FF40H

of

VAC

for

and

Radio

4-16

simply

dual

It

60

use

of
is
the

Shack

shows

is

Hz
by

of

WHITE +5V

YELLOW

Figure

GREEN

RED

BLACK

4-16.

Joystick

A

3 1

100K

Schematic

-----------1tad1elhaell----------

B

GND

3

100K

GND

LUG

-

55

-

Color

computer

-----------TRS-80

The

mechanical
changed
two-dimensional
so

that
variable
This

the

a

momentary

at
a 5

allows

handle

the

resistor,

is

2

assembly
same

control.

volt
the

center

moved.

ground

time.

reference

and

ground

wiper

The

contact

allows

This

The

potentiometers

is

applied
is

to

push-button

for

®

both

gives

connected

vary

an

input

Service

potentiometers

the

effect

are

to

one

side

to

the

from

0

switch

signal.

to

merely

to

of

connected

of
other.

5

volts

Manual

be

a

the

as

provides

4.16
The

with

TV
the
TV
computer
the
schematic

TV

antenna

connectors

antenna,

customer's

antenna

phone

INPUT

COMPUTER

Switch

is

output

plug
of

FROM

Box

switch

and

attached

the

box

provided

the

TV

through

is

connected

input

antenna

home TV.

on

,----

1

I

I
I

I I

L

_______

BALUN

consists

for

the

directly

the

switch

switch

of

attachment

The

switch

300

ohm

to

through

box.

j

a

switch

twin-lead

the

a

box.

60 dB

SWITCH

I I

to

the

box

switch
75

ohm

Figure

I

and

computer,

is

box.
coax

a

balun,

connected
output.

The

cable

4-17

shows

TWIN LEAD OUTPUT

TO

THE

the

to

The

to

a

TV

ATTENNA

300

INPUT

ohm

>>-,_-------------'V"'

----~~~~~~~~-r-u~'

>

Figure

From
switch
inpedance
signal
specially
required

the

box

is

computer,

which
to
then
designed

between

-----------ltadle

4-17.

matches

a

TV's
connected

the

the

signal

300

to

provide

computer

Antenna

the

modulator's

ohm

antenna

to

the

-

J

~-'-~~o

Switch

is

connected

switch.

the

60

and

the

lhaell----------

56

-

Box

input

dB

TV

Schematic
to

75

ohm

impedance.

The

switch

of

isolation

antenna.

a

balun
output

is

in
This

the

Color

Computer

-----------TRS-BO

2 ®

"

-----------

Service

Manual

Main

Logic

PCB

#8857625

(8857636*),

Color

Computer

2

=======================================================

Item

Ref

Description

Part

Number

=======================================================

1 1

2
3
4
5 2
6

7
8 1
9 1
10
11

CAPACI'rORS

1

9
3

5

1

2
1

Cl
C2
C3
C4

cs

CG

C7

ca

C9

ClO

Cll
Cl2
Cl3
Cl4
Cl5
Cl6
Cl7
Cl8
Cl9
C20
C21
C22
C23
C24
C25
C26
C27

PCB,
Lug,
Socket,
Socket,
Socket,

Socket,
Switchcap

Bracket,
Heats
Nut,
Label,

220
4700

0.1

0.1

100

0.1

0.02

0.02

0.02

0.02

100

N.A.

0.02

0.02

0.1

0.02

0.02

0.1

0.1
10

0.1

0.02

0.02

0.1

0.1

0.001

0.02

Main
Fast-On

U22,23)

ink,
#6 KEPS

mfd,

mfd,
mfd,
mfd,
mfd,
mfd,

mfd,

mfd,

mfd,

mfd,

mfd,

mfd,

mfd,

mfd,

mfd,

mfd,

mfd,
mfd,

mfd,

mfd,

mfd,

mfd,

mfd,
mfd,

mfd,

mfd,

Logic

16-Pin

20-Pin
24-Pin
40-Pin

(Reset)

Switch

6015-PBSEl

PCB

Serial

16V

16V
50V
50V
16V
50V

50V
50V
50V
50V

16V

50V
50V

50V

50V

50V
50V
50V

25V

Elec

50V

50V

50V
50V
50V

50V

50V

DIP(Ul,14-21)
DIP(U3,5,6)
DIP(Ul2,13)
DIP(U2,7,8,

(Reset)

Elec

Mono
Mono

Elec
Mono

Elec

Mono

Mono
Mono

Mono

Mono
Mono

Elec

Cer
Cer
Cer
Cer

Cer

Cer

Cer
Cer

Cer
Cer

Poly

Cer

Rad

Rad
Axial
Axial
Rad
Axial

Disk
Disk

Disk

Disk

Rad

Disk
Disk

Axial

Disk

Disk
Axial
Axial

Rd

Axial

Disk

Disk

Axial
Axial

Disk

NP

(Ql)

8709416
8529016
8509003
8509009
8509001
8509002

8489066
8729223
8549016
8579004

8789963

8327221

8328471

8374104
8374104
8327101
8374104
8303223
8303223
8303223
8303223
8327101

8303223
8303223
8374104
8303223
8303223
8374104

8374104
8396101
8374104
8303223
8303223
8374104
8374104
8352104

8303223

*Extended

Basic

-----------lladtelhaell----------

PCB

Number

-

67

-

__

c_o_1o_r_c_o_m_p_u_t_e_r_2

____

TRS-BO

®

______

s_e_r_v_i_c_e_M_a_n_u_a_l_

Main

Logic

PCB

#8857625

(8857636*),

Color

Computer

2

=======================================================

Item

Ref

Description

Part

Number

=======================================================

CAPACITORS

C28
C29
C30
C31
C32

C33
C34
C35

C36
C37

C38

C39

C40
C41
C42

C43

C44

C45

C46

C47

C48 1

C49

cso
CSl
C52
C53
C54
C55
C56
C57
C58
C59
C60
C61
C62

(cont'd)

mfd,

0.1

0.1

mfd,

mfd,

0.1
N.A.

mfd,

0.1
mfd,

0.1

0.1

mfd,

mfd,

0.1

0.1

mfd,

pfd,

~3

pfd,

56

pfd,

56

0.1

mfd,

N.A.
N.A.
9-35
39

pfd,

0.1

mfd,

10

mfd,

0.1

mfd,

mfd,

N.A.

mfd,

0.1
mfd,

0.1
mfd,

0.1
mfd,

0.1
mfd,

0.1
mfd,

0.1
mfd,

0.1
mfd,

0.1
mfd,

0.1
pfd,

150

pfd,

33

150

pfd,

10

mfd,

pfd

sov
sov

sov

50V

50V

50V
sov
SOV

SOV
50V
SOV

SOV

Trimmer

SOV

SOV

25V

50V

SOV

sov
sov
sov
sov
sov
sov
sov
50V
sov
SOV

SOV

SOV

25V

Mono
Mono
Mono

Mono
Mono
Mono
Mono

Mono
Cer
Cer
Cer

Mono

Cer

Mono
Elec

Mono

Elec

Mono
Mono
Mono
Mono
Mono
Mono
Mono
Mono
Mono

Cer

Cer

Cer

Elec

Axial
Axial
Axial

Axial
Axial

Axial

Axial

Axial
Disk
Disk
Disk

Axial

Disk

Axial

Rad

Axial
Rad

Axial

Axial

Axial

Axial

Axial

Axial

Axial
Axial
Axial

Disk

Disk

Disk

Rad

8374104
8374104
8374104

8374104
8374104
8374104
8374104
8374104
8300334
8300564
8300564
8374104

8360356
8300394
8374104
8326102
8374104

8325104
8374104

8374104
8374104
8374104
8374104
8374104
8374104
8374104
8374104
8301154
8300334
8301154
8326102

CONNECTORS

J3
J4
Jl
J2
JS

JG

4-Pin

5-Pin

6-Pin
6-Pin
Keyboard
40-Pin

DIN
DIN
DIN
DIN

Right

Angle

lladle lhaell

-

68

-

8519094
8519085
8519095
8519095
8519176
8519139

__

c_o_1_o_r_c_o_m

....

p._u_t_e_r_2

____

TRS-BO

®

_____

s_e_r_v_i_c_e_M_a_n_u_a_l_

Main

=====================================================~==

Item

Logic

Ref

PCB

#8857625

Description

(8857636*),

Color

Computer

Part

Number

2

========================================================

DIODES

CRl
CR2
CR3
CR4
CRS
CR6
CR7
CR8
CR9
CRlO
CRll

CR12

CR13

FBl
FB2
FB4
FB7

1N4002,
1N4002,
1N5401,
1N5401,
1N4148
1N4148
1KF20-04
1KF20-04
1N4148
1N4148
1N4148
1N4148
1KF20-04

Ferrite
Ferrite
Ferrite
Ferrite

sov,
sov,

lOOV,
lOOV,

Bead
Bead
Bead
Bead

lA
lA

3A

3A

8150002
8150002
8160401
8160401
8150148
8150148
8160020
8160020
8150148
8150148
8150148
8150148
8160020

8419013
8419013

8419013
8419013

Kl

TRANSISTORS

Ql

Q2

RESISTORS

Rl
R2
R3
R4
RS
R6

R7

R8
R9
RlO
Rl l
Rl2
Rl3
Rl4
Rl5
Rl6
Rl7

Relay

SJ5812
MPS3904

51

ohm,

0.1

ohm,

270

ohm,

510

ohm,

4.7

kohm,

4.7

kohm,

10

kohm,

10

kohm,

1

kohm,

9.1

kohm,

1

00

ohm,

4.7

koh

10

ko

hm,

4.7

kohm,

1.5

ko

10

koh

m,

4.7

kohm,

1/

l/4W

m,

hm,

4W

5 %
l/2W
l /
l /

l/4W
l /

l /
l/

l/4W5%

4W

4W
l/4W
l/4W

4W

l /

4W

2W

l/4W

4W

l/

4W

l/4W
l/4W

5%
5%
5%

5%
5%

5%

5%

5%

5%
5%

5%
5%
5%

5%

5%

8429107

8110569
8110904

8207051
8247002
8207127
8207151
8207247
8207247
8207310
8207310
8207210
8207291
8217110
8207247
8207310
8207247
8207215
8207310
8207247

----------1tad1elhaeli----------

-

69

-

Color

Computer

-----------TRS-80

2

®

-----------

Service

Manual

Main

Logic

PCB

#8857625

(8857636*),

Color

Computer

2

========================================================

Item

Ref

Description

Part

Number

========================================================

RPl

Sl
S2

Ul
U2
U3
U4

us

U6
U7

u0

U9

UlO

Ull

Ul2

Ul4

thru

21

U22

U23

(cont'd)

4.7

kohm,

100

ohm,

100

kohm,

4.7

kohm,

100

kohm,

220

ohm,
ohm,

150

ohm,

100

ohm,

Res

Pack,

DPDT,
SPST,

CIRCUITS

Custom

MC6821,

Custom
NE555
74LS273,
74LS244,
MC6822,
MC6847,
RF

Modulator

74LS02,
74LS138,
MC68A364,
MC68A364,

MCM4517,

MC6883,
MC6809E,

l /

4W

l/4W

l /

4W
l/4W
l /

4W

l/2W

1 I 4 w s %

l/4W
l/4W

4.7

Push
Momentary

SALT

PIA

DAC

Octal

Buffer
PIA
VDG

Quad

Decoder

ROM
ROM

RAM

SAM

CPU

ON/OFF

NOR

5%

5%

5%
5%
5%

5%

5%
5%
kohm,

Latch

10

Pin

8207247
8207110
8207410
8207247
8207410
8217122
8207110
8207115
8207110
8294247

8489062
8489065

8050527
8040821
8050526

8040055
8020273
8020244
8040822
8040847
8429500
8020002
8020138
8040364B
8042364A
8040517

8040278
8040809

RESISTORS

Rl8

Rl9
R20
R21
R22
R23

R24 1 o o

R25
R26

SWITCHES

INTEGRATED

*Ul3

*Used

Yl

on

Crystal,

#8857636

-----------1tad1elhaell----------

14.31818

Extended

Basic

- 70 -

PCB

8409008

only

__

c_o_1_o_r_c_o_m_p_u_t_e_r_2

5/

Troubleshooting

____

TRS-BO

®

Service

Manual

This
diagnostic
Computer

waveform

5.1
The

technicians.

computers

dual-trace

computer,
problem
because
desired

fault.

thoroughly

2,
available

technician

Standard

Identify,

consists

this

save

cable

problem.

exist,

observing

defective

equipment,

section

INTRODUCTION

Color

as

well

step
hours

was

Localizing

of

the

routines,

2.

Scope

diagrams.

Computer

Throughout

will

it
and
a

particular
by
It

from

troubleshooting

Localize,

largely

it
bad,

After

the
component

be

oscilloscope.

is

important

a

software

the

user,

is

therefore

familiar

as

the

Radio

in

the

of

is

wise

of

troubleshooting

or

identifying

symptoms.

and

sometimes,

manual

and

settings

2

should

assumed,

problem.
program
the

with

Theory

Shack

servicing

and
making

to
that
can

it

usually

will

contains

scope

this

As

to

hardware

recommended

the

of

techniques

Isolate.

check

was

Isolating
often

part

waveforms

are

noted

be

serviced

guide

as

will

is

true

distinguish
does

operation

Operation.

National

of

the

sure

that
the
time
some

that

be

involve
substitution.

Stated

a
accomplished

troubleshooting

for

on

the

only

a

basic

the

ability

when

not
is

not

that

Parts

Color

include

The

a

obvious.

only
other
problem

a

problem

servicing

between

another

yield

necessarily
the

of

the

Diagnostic

to

Computer

first

problem

to

relatively

the

the

Color

individual

by

qualified

knowledge

to

a

way,

the

results

technician

Color

assist

the

steps

step,

exists.

Doing

find

really

use

out

by

down

of

merely

hints,

of

use

a

any

hardware

just

at

Computer

aids

the

2.

Identify,
so

can

that

minor

does

to

the

test

be
are

In

a

Following

might
Video

Keyboard
Processing
cassette
RS-232
Sound
Joystick
cartridge

be

identified

is

a

problems

problems

----------ltad1elhaell----------

list

of
on

virtually

the

Color

-

71

all

of

Computer

-

the

problems

2:

that

__

c_o_1_o_r_c_o_m

...

p._u_t_e_r_2

____

TRS-BO

®

Service

Manual

If

a

problem

exists

in

more

than

one

area,

the

first

course

of

action

should

be

to

look

for

a common

cause.

Although

it

is

possible

to

have

two

or

more

independent

problems,

it

is

more

likely

that

a

single

failure

can

cause

a

multitude

of

symptoms.

It

is

apparent,

for

example,

that

if

the

power

supply

is

dead,

that

all

of

the

above

areas

will

have

problems.
Once

a

problem

has

been

identified

in

one

of

the

above

areas,

it

can

be

localized

by

observing

the

specific

symptom.

For

example,

if

a

Cassette

problem

exists,

is

it

a

Read

problem,

a

Write

problem,

or

a

Motor

Control

problem?

After

the

problem

is

localized,

isolating

it

to

a

specific

component

is

usually

not

very

difficult.

Included

in

this

section

is

a

flowchart

for

verifying

proper

operation

of

the

power

supply,

oscilloscope

pictures

of

various

signals

under

proper

operation,

and

a

textual

description

of

symptoms

one

might

expect

along

with

probable

causes.

5.2

Video

Problems

5.2.1

No

Display

One

of

the

first

indications

that

the

Color

Computer

2

is

working

is

the

display

on

the

T.V.

If

upon

powerup

the

T.V.

continues

to

display

"snow",

indicating

that

it

is

not

receiving

a

signal

from

the

computer,

the

first

thing

that

should

be

done

is

to

check

the

obvious.

Is

the

proper

channel

selected

on

the

T.V.

and

the

computer?

Is

the

coaxial

cable

connected

from

the

computer

to

the

T.V.

switchbox?

Is

the

switchbox

connected

to

the

VHF

inputs

of

the

T.V.?

Is

the

switchbox

in

the

"computer"

position?

On

sets

requiring

it,

is

the

75

ohm

VHF

link

connected

to

enable

the

300

ohm

inputs?

If

the

answer

to

each

of

the

above

questions

is

yes,

then

either

the

power

supply

or

the

modulator

is

dead.

In

this

case,

a

quick

check

for

the

presence

of

+5

volts

at

the

left

side

of

C32

should

suffice

to

determine

whether

the

power

supply

or

the

modulator

is

at

fault.

If

the

+5

volts

is

there,

then

the

modulator

should

be

replaced.

If

the

voltage

is

incorrect

or

missing,

proceed

to

the

section

on

checking

the

power

supply.

-----------1tad1elhaell----------

-

72

-

__

c_o_1_o_r_c_o_m_p_u_t_e_r_2

It

is

also
screen
this
computer,
the

possibility

fault.

"gotcha"
both
contrast
these
the
Figure
is
then
the
shorts

case,

power

the

Y

the

US

power

are
signal

possible

remaining

the

which

supply

that

There

--

check
T.V.
of

the

O.K.,

at

5-6.

most

is

or

If

likely

probably
supply
opens

____

snowy,

T.V.

indicates

and
one

is

also

that

and

the
T.V.
then
pin
the

(do

associated

to

have

it

is

at

modulator.
or

the

the

the

computer,

are

get

2S

of

Y

signal

suspect.

at

fault.

a

complete

TRS-BO

no

video,

is

completely
least
at

least

other

possibility

proper

set

at

out

the

US. A

is
If

Other

with

®

but

receiving

partial

However,

of

these

of

channel

and

that

an

appropriate

oscilloscope

normal

present,

the

Y

signal

possibilities

check)

US

and

and

the

instead

black

a

signal

functioning

there

components

some

is

selected

the

brightness

Y

signal

then

circuit
modulator.

Service

or

is

obvious

level.

and

is

the

is

missing,

Manual

of

the

blank.

from
still

check

modulator

include
board

the

of

is

on

and

If

for

shown

In

the
at

in

5.2.2
If

is
suspect
there
and
out
signal
proper
in

(US)

also
If

frequency,

5.2.3
In

indicates
this
require
example,
executed
also
should
function,

the
rolling

is
the
the

must

Figure

is
remotely

the

many

is

start

No

frequency

clock

stop

Sync

image

is
computer

3.5S

bad,

"Garbage"

cases,
the

screen

on

vertically

US

one

obvious

MHz

be

5-5.

or

signal

proceed

a

processing

case,

"SOUND

directly

the

at

proceed

the

or

the
set

clock

at

the

C3.5S

If

the

the

possible

to

on

a

screenful

try

output

60,20"

if

cassette

the

end.

to

screen

or

clock

thing
to

the

signal

proper

MHz).

clock

Y

signal

that

is

missing,

the

Screen

problem.

some

to

or

one

and,

the

is

not

diagonally),

signal

to

check

same

going

amplitude

A

normal

is

o.

is

loaded

the

modulator

or

section

of

"garbage"

simple

prove

some

types
If

section

they
similar

carefully.

if

tests

a

synchronized

then

going

channel?

K.,

the

on

To

commands

short

like

on

to

first
into

(TTL
clock
then
by a PC

wrong

checking

(random

verify
are

working.

sound

program

these

Processing

the

US.

-­If

pin

level)

either

is

whether

that

"CLOAD"

properly

most

Of

course,

are

amplitude

command

do

the

so,

33

of

signal

short.

bad.

the

characters)
do

is
not

Problems.

then

US.
and

the

clock.

or

not

For

should
loaded,

likely

T.V.

scope
the

is

shown

VDG

It

or

not

may

Cit

This

is

be

-----------1tad1elhaell-----------

- 73 -

Color

Computer

2 ®

Service

Manual

-----------TRS-BO

R

-----------

If

the

above

tests

indicate

that

the

processor

is

functioning

normally,

then

the

problem

is

likely

caused

by

either

bad

RAMs,

(Ul4

-

21),

a

bad

latch

(U5),

or

a

bad

VDG

(U8).

Substitution

with

known

good

RAMs

should

be

used

to

isolate

a

RAM

problem.

For

the

other

two

possibilities,

an

oscilloscope

should

be

used

to

check

all

signals

for

valid

TTL

levels.

The

latch

should

be

clocked

by

the

RAS*

signal,

which

also

appears

at

pin

4

of

the

RAM

chips.

If

a

bad

logic

level

is

found,

then

the

chip

producing

the

logic

level

is

suspect.

If

no

problem

is

found

with

the

RAMs

or

the

latch,

the

VDG

should

be

checked

by

substitution

(again,

with

a

known

good

IC).

5.2.4

Clear

Screen,

No

Signon

When

the

Color

Computer

2

is

first

powered

up,

it

clears

screen

and

prints

the

appropriate

BASIC

signon

message.

the
If

the

screen

clears,

but

the

signon

fails

to

appear,

there

is

most

likely

a

processing

problem.

Particularly

suspect

would

be

an

active

FIRQ*

without

a

cartridge

present.

Proceed

to

the

section

on

Processing

problems.

5.2.5

No

Color

Before

attempting

to

fix

a

no-color

problem

in

the

computer,

ensure

that

the

T.V.

is

properly

adjusted.

The

color

level

control

must

be

set

to

an

appropriate

level

and

the

tint

control

should

be

approximately

centered.

The

fine

tuning

control,

if

present,

must

be

properly

adjusted,

or

no

color

will

appear.

It

is

a

good

idea

to

try

the

computer

on

both

channels

(3

and

4)

to

determine

if

it

is

merely

an

adjustment

problem.

Also

note

that

the

computer

will

not

generate

color

on

a

T.V.

that

depends

on

the

vertical

Interval

Reference

(VIR)

signal

to

be

present.

Some

T.V.s

that

use

the

VIR

signal

to

automatically

adjust

the

color

have

a

switch

to

defeat

this

feature;

others

do

not.

If

the

VIR

option

cannot

be

defeated,

then

color

will

not

be

produced

on

this

T.V.

as

the

computer

does

not

generate

the

VIR

signal.

If

color

is

produced

on

one

channel

and

not

on

another,

it

should

be

determined

whether

the

computer

or

the

T.V.

is

at

fault.

This

may

be

done

by

trying

several

computers

on

the

T.V.,

or

by

trying

the

computer

on

several

T.V.s.

If

the

computer

is

determined

to

be

at

fault,

the

modulator

should

be

replaced.

-----------

lladle

lhaell----------

-

74

-

__

c_o_1_o_r_c_o_m

If

the
possibilities
presence
A

scope

missing,

will
this

leaking,

which

even

...

p,_u_t_e_r_2

computer

of

picture

or

produce

include

or

is

the

produce

exist.

the
less

a
Rl3

the

SAM
a

____

does

3.58
is

shown

than

black

open

modulator

chip,

black

TRS-BO

not

The

MHz

100

and

or

is

and

generate

first

clock

in

Figure

mV

p-p

white

increased

itself.

not

working

white

®

color

thing

into

picture.

picture.)

the

5-5.

amplitude,

in

(If

on

to

check

modulator

If
Probable

value,

the

the

system

Service

any

the
the

C61

clock

T.V.,
is

the

(pin

clock

modulator

causes
shorted
source,

will

Manual

several

A).

is

for
or

not

After
thing

VDG.
greater
about
10,

Figures

levels

(photographs

green).

levels,
cure
shorts

5.2.6
The

the

properly

control,

VDG.

caused
resistors,

determining
that
The

than

3/4

respectively,)

5-6

of

the

the

or

Wrong

procedure

same

Note

by

should

Ch B

0

to

1

thru

Phase

are

If

any
VDG

problem,

again,

Colors

for

as

that
adjusted,
and

then

that

the

Artifacting

capacitors,

the

clock

be

checked
output
volts
volt.

5-9.

A

and

given

of

is

possibly

for

check

an

(pin

and

The

outputs

Phase

the
suspect.

then

troubleshooting

no

paying

irregularity

9)

probably

Phase

should

Note

for

screen

signals
the

signals

a

color.

particular

the

circuit

and

diodes).

signal

is

the

should

A

that
B

bad

chroma

the

determines

are

If

replacing
modulator.

Insure

of

to

be

Chroma

be

less

and

Phase

display

relationship

colors

missing

are

wrong

attention

signals

the

(04,

O.K.,

outputs

some

than

waveforms

the
of

or

the

loaded

colors

that

coming
Phase
Q2,

and

the

next

of

steady

2

volts--usually

B

(pins

of

color

red,

the

blue,

at

improper
VDG
by

either

is

T.V.

to

A

signal
associated

does

basically
the

out

the

DC

value

11

and

shown

the

and
not

is

tint

of

may

in

DC

PC

the

be

5.2.7

The

responsible

mode,

of
the

wrong

a

different

is

(04)

No

artifacting

so

the

artifacting

following

color

obtained

is

not

Artifacting

for

that

this

symptoms:
all
color

in

operating,

-----------1tad1e

circuit
generating

mode
circuit

the

time,

from

the

high-res

Or

in

will

no
the
or

Improper

the

Color

burst

be

could

color

or

left

rest

mode,

the

transistor

lhaell-----------

-

Artifacting

in

the

displayed

result

in

part

of

the

then

75

-

Computer

high-resolution

in

in

one

the

high-res

of

the

screen.

either

(Q2)

2

is

color.

or

screen

If
the
is

Failure

more

mode,

shaded

no

one-shot

not

of

color

__

c_o_1_o_r_c_o_m

... p ...

u_t_e_r_2

____

TRS-BO

®

Service

Manual

coupling
theory
circuit
circuit

symptom

a

different

indicates
causing
portion
defective
or

by

increase

5.3

5.3.1

No
These
main

resistor
of
particular,

button
problem.

Keyboard

keyboard

include:

PCB,

the

this

of

operation
works.)
are

shown

is

that

color

that
the

level

of

the

U4,

No

Keyboard

entry

defective

pack

keyboard

note

leads

signal

Oscilloscope

in

of

from

the

of

video

by

leakage

in

value

may

broken

RPl,

row

that

CC15

and

onto

for

a

Figures

the

left
the

one-shot

Phase
display.

of

Entry

be

flex

PIA

U7,

defective

inputs,

the

Cl8)

Phase
detailed

pictures

5-10

side

rest

is

A

to

or

improper

resistor

caused

cable
+5

RPl,

or

capacitors

might

A.

of

taking

be

This

by a variety
volt
a

(Consult

description

of

thru

of

the

the

too

shifted

may

value

RlO.

which

connection

a

short

defective

on

short

5-12.
screen.

and

the

the

screen

long

during

be

caused
of

of

connects

to

ground

keyboard.

the

joystick

cause

earlier

of

how

artifacting

One

strange

being

This

to

time

the

by

capacitor

factors.

keyboard

to

pullup

on

this

this

shaded

out,

active

a

C26,

to

any

In

fire

5.3.2
The

most

do

is

an

in

the
isolated
on

the
of

keys
schematic
Other

RPl.

5.3.3
If

that

most

keyboard
the
One
section,

possible

a

different

should
likely

aforementioned
additional

Some

connecting
keyboard

Wrong

Keys Inoperative

common

open

key

does

itself,

particularly

somewhere

does

not

diagram),

Character

be
a

short.

cause

flex
not

itself.

work

then

causes

character
displayed

in

the

possibilities

possibility

of

some

--

cable,

work,

However,

(see

any

are

a

for

is
for

Again,

connector,

on

the

keys

either

or

the

problem

the

keyboard

of

the

defective

Key

Pressed

displayed

a

given

the

is

a

defect

data

not

on

the

on

the

if

a

above

key,

short

or

should

bus.

working

keyboard

PC

is

whole

matrix

is

PIA

other

the

could

on

the

also

in

the

board.
almost

row
a

CU7)

than

be
PCB.

be

when

on
possibility.
and

problem

processing

others

itself,

If

certainly

or

column

the

defective

the

one

on

the
All

checked.

or

an

is

of

-----------1tad1e

lhaell----------

- 76 -

___ c __

o_1_o_r

__

c_o_m_p_u_t_e_r

___ 2 ______

__,,.Fl!S-EiCJ ®

___________

s_e_r_v_1_·c_e

__ M __

a_n_u_a_1

___

5.4

5.4.1
Processing

is
valuable
is

determine

that
half-level
case
outputs,
Observe
5-16.
trace)
to

In
the
it
appropriate
absolutely
the
going
exactly
sync
time
the
previous
to

is

the

Processing

General

because
the

oscilloscope.
the
of

Note

goes

a

valid

addition

signal

sometimes

picture

blip

pedestal

is

blip

generate
Figure

E

and

problems
there

tools

whether

high

tri-state

when

the

the

measured

is
discussion

and

almost

not
scope
that
to

logic

to

is

happening

gets

combination

necessary.

of

of

same

of
exactly
color

5-4,

Q

signals.

Problems

are

for

there
low
always
outputs.
tri-stated,
picture

although

a

half-level
0

showing

rather

Y

and

the

Phase

time
Y
on

burst.)

which

are

the

so

many

locating

In

is

levels

and

up
valid

at
of

As

Phase

B

as

(top

the
under
that

shows

trace).

horizontal

most

possibilities.

the

cause

many

indicates

complicated

the

this

cases,

activity

are

Even

should

of

the

the

data

at

to

a

levels,

the
signals,

an

example,

B.

signal

back

the

back
is

Another

the

memory

times,
valid

appropriate

Note

quadrature

difficult

of

it

on a given

valid

a

problem,

a

signal

go

output

that

logic
a
to

this

observe

that

(bottom

porch

This

where

is
axis
porch.

example

to

processing

is

sufficient

TTL

levels.

with

to

valid

signals,

line

it

1

scope

time.

trigger

is

possible

the
trace)

of

the

evident

of

the

(Recall

this

that

relationship

isolate.

One

line,

except

tri-state

(bottom

also

at
can

Figure

small

horizontal
scope,

blip

of

the
problems

and

A

in

TTL

levels.

Figure

goes

other

tell

Although

off

the

if

5-6,

negative-

happens

because

from

needs

shows

This
most

to

the

down

times.

you

at

and

the

to

timing

of

if

be

5.4.2
There

problems:

nothing),
instructions

it
correctly,
caused
items,
processing
problem.

is

Symptoms

are

several

the

it

supposed

but

by

the

instead

check

processor

may

and

to
not

same

of

-----------------------------~nad1elhaell------------------------------

common

"go

wild"

appear

be

doing),

quite.

type

being

list

symptoms
may

to

of
listed

for

"lock

(randomly

be

doing

or

Any

of

defect.

by

any

type

-

77

of

up"

something,

it

may

these

Therefore,

symptom,

of

-

processor-type

(appear

execute

function

symptoms

comprise

processor-related

to

garbage

but

the

do

not

"almost"

may

be

following

a

what

____

c_o_1_o_r

__

c_o_m_p_u_t_e_r

___ 2 _________

"TFl!S-EICJ

®

___________

s_e_r_v_i_·c_e

___

M_a_n_u_a_l

___

5.4.2.1

E

and

Q

Check

for

the

presence

of

E

and

Q.

These

signals

should

look

like

the

ones

in

Figure

5-4.

If

either

clock

is

missing,

the

CPU

will

not

operate.

Also

make

sure

that

the

clocks

have

good

logic

levels.

The

E

clock

is

more

demanding

than

the

Q

clock,

and

requires

a

high

logic

level

of

at

least

4

volts.

These

clocks

are

produced

by

the

SAM

chip

(U22).

Eis

sent

to

both

PIAs

(U2

and

U7),

the

CPU

(U23),

the

NOR

gate

CU10)

and

the

edge

connector.

The

Q

clock

goes

only

to

the

processor

and

the

edge

connector.

Both

clocks

have

small

value

capacitors

on

them

to

prevent

harmonic

radiation.

If

any

of

these

components

connected

to

these

clock

lines

become

shorted,

it

is

likely

to

reduce

the

amplitude

of

the

clock

signal.

5.4.2.2

Interrupt/Halt/Reset

After

power

up,

without

a

cartridge

installed

and

without

executing

any

program,

the

NMI*

line

(pin

2),

the

FIRQ*

line

(pin

4),

the

HALT*

line

(pin

40),

and

the

RESET*

line

(pin

34)

of

the

processor

should

all

be

high.

In

addition,

the

IRQ*

line

(pin

3)

should

have

a

60

Hz

pulse

on

it

Cit

should

have

a

short

low-going

pulse

about

every

16

msec).

If

any

of

these

lines

are

stuck

low,

you

have

found

the

problem.

Replace

the

processor.

If

the

condition

still

exists,

find

out

what

is

pulling

the

line

low,

and

repair

it.

If

the

IRQ

line

is

low,

the

PIA

U7

could

be

bad,

or

a

problem

could

exist

in

the

address

decoding

section.

(Once

the

PIA

generates

an

interrupt,

the

processor

must

access

the

PIA

to

clear

the

interrupt.)

5.4.2.3

Address/Data

Lines

It

is

rather

difficult

to

define

exact

patterns

of

address

and

data

lines

on

the

CPU

as

these

are

dependent

upon

which

address

is

being

accessed,

and

the

data

to

be

read

or

written.

All

address

and

data

lines

should

be

capable

of

activity,

however,

and

the

output

levels

should

be

valid

TTL.

Figures

5-13

and

5-14

show

typical

address

and

data

patterns.

Note

that

some

of

the

address

lines

may

not

show

activity

when

the

processor

is

in

a

loop.

However,

by

depressing

the

RESET

button

while

scoping

the

address

lines,

at

least

momentary

activity

should

be

displayed.

Another

clue

is

that

typically

(although

certainly

not

always)

the

address

lines

should

act

more

or

less

like

a

frequency

divider

--

that

is,

the

frequency

of

activity

on

Al

should

------------------------------~ad1elhaell-------------------

-

78

-

Color

Computer

-----------TRS-BO

be

half

frequency

accesses

is

altered.

If

any

generating

is

indicated.

(U23),

probably

the

frequency

of

instructions

of

the

either

then

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shorted,

2

A2,

address

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device

and

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the

or

of

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on.

sequentially

or

data

valid

which

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logic

fault

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lines

persists

is

on

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of

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or

the

PCB

®

-----------

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because

until

seem

valid
after
appropriate

short.

and

twice

the

the

program

incapable

logic

replacing

Service

the

processor

0,

bus

counter

of

a

the
is

Manual

fault

CPU

5.4.2.4
If

the

CPU
correct
PIA,
evident.
accepting
accessing
Keyboard
enable
the
signals
the
should
through
Ull

inputs
is

output

5.4.2.5
If

signals
does
or
substitution
could
problems,
execution,
committed,
two
or
typical
shown

etc.)

line

PIA
3-to-8

be

can

and

that

signals

the

ROM

clear

RAM

problem

also

cases

command

in

Address

is

functioning

addresses,

is

not

During

keyboard
the

ROM

PIA

chip

is

S2
be

the

Memory

are

RAM

(U7,

(Ul2,

enable
absent,
decoder

checked

lines
easily
outputs,

ROM

is

good,

but

with

be

such

the
and

require

before

waveforms

Figures

being

responsible

Decoding

but

selected,

the

entry),

(Ul2,

looking

pin

(U7,

likely

(Ull)

by

(pins

checked

as

(Ul2)

of

Ull,

Problems

enabled

but

the

signon

is

indicated.
known

as

intermittent

display

incorrect

careful
assuming

5-15

Section

normally,

the

appropriate

a

"idle"

20)

substitution,

25,

can

and

or

the

of

(RAS, CAS,

and

the

to

obtain

for

should

pin

suspects

or

26

with

Ul2.
the
that

screen
does

good

for

error

results

analysis

a

5-16.

mode

23).

the

frequently

devices.

ROM

outputting

processing

(after

CPU

should

instructions)

keyboard

show

If

are

NOR

gate

or

and

27)

an

oscilloscope

A

PIA

These
other

(U7)

PCB

never

not

lock-up,

messages

of
or

DATA

final
faults

appear,

should

processing

computations.

of

RAM

device

problem

power

be

entry).
activity,
either

the

SAM

(UlO).

by

observing

on

the

remote

are

loading

exist.

and

all

clears

then
be

ROM

and

random

when

the

attempted

problem.

IN,

and

all

of

(ROM,

up

alternately

of

chip

oscilloscope.

for

other

or

checked

RAM

type

(garbage)

no

DATA

RAM,

will

but

before

and

the

The

ROM

as

should

these

CU22),

The

SAM

the

proper

possibility

the

CPU

the

screen

either

faults

error

The

program

Some

OUT)

the

be

SO

a

by

was
last

chip

ROM

are

-----------

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-

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Manual

5.5

5.5.1
Of

motor
course,
bad
can
depressing
continuity
pins)
is
heard,
relay
following
components:

After
a

then
the
If
suspect
fault

Cassette

Motor

all

possible

control

the
cable
be

tested

of

bad

or
then

itself

10

POKE

20

POKE

30

GOTO

this

squarewave

change

same

it

is

component

is

Problems

Control

problems

is

probably

obvious

or

bad

cassette

by

listening

the

Reset

does

the

the

simple

program

squarewave.

there,
indicated.

not

cassette

PCB

possible

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program

65313,60
65312,52

10

of

approximately

U2.

then

or

coil),

is

If

does

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in

should

button.

appear

connector,
connector
bad

components
will

keyed

it

is

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it

change

not

the

the

easiest

not

be

recorder.

for

the

If

at

pins

is

as

well

allow

in

and

40

present,

is

not

the

correct

Color

overlooked,

Actuation

relay

the

click

1

and

J4,

relay.

open.
as

run,

Hz.

then
there,

the

then

are

PCB

checking

Computer
to

isolate.

click

is

3

(the

either

If

the

U2,

Ul,

faults.

scope

If

it

is

scope

then

If

replacing

problem,

2,

which

of
while

heard,

of

U2

not

Ul

change

lack

the

two

the
click
and

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these

pin

pin

then

of

Of

includes

relay

but

outside

relay

is

the

39

present,

9

for

Ul.
the
a PCB

not

for

5.5.2
Cassette

repair.
the
a

cassette

following

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top
directly
not

indicated.
pin
re-run

Write

write
Again,

cassette

program:

10

SOUND

look

waveform

at
17

the
is

the

for
at

not

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problems

don't

recorder

write

the

connector,

If

program.

problem

200,255:GOTO

the

waveforms

is

there,
chip

it

shorted

is

are

forget

and

but

(U3

a PCB

not

to

If

the

also

to

cable.

exists,

10
as

the

pin

17).

fault
present
ground.

waveform

very

verify

key

shown

bottom

at

If

you

in

in

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or

connector

the

If

not,
is

simple

one

it

-----------1tad1elhaell----------

the

obvious,

are

and

Figure

isn't,

is

chip,

replace

still

to

isolate

convinced

execute

5-17.

look

at

the
fault

insure
not

such

the

If

for

chip,

is
that

U3

and

present,

and

as

that

the

it

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____

TRS-BO

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Manual

then
cassette
2

5.5.3
Isolating

difficult.

some
signal
microfarad,
as

bottom
Ul),
as

but

CUl).

faults
Remember,

should

valid

volts

above

the

not

replace

Read

kind.

coupled

waveform

then

PCB
If

or
be

TTL

PIA

output

p-p.

Problems

a

cassette
However,

A

non-polarized

and

look

check

and

the

output
the
PIA
the
at

least

levels.

U7

and

amplitude

sufficient

back

connector.

output
U2

input

to

for

is

not

input

waveform,

to

be
must

100

repeat

should

read
to

is

problem

do

so

signal

the

cassette

capacitor.

the

waveforms

present

components

If

still

loading

go

mv

p-p.

the

requires

the

then

not

the

both

be

can

(the

C23,

above

Also,

test.

somewhere

is

not

an

be

the

input

Run

in

Figure

input

R23,
input
replace

present,

output

and

the

Remember

between

much

waveform

more

input

cassette
through
the

same
5-18.

to

the

and
the

SALT

then

waveform.

below

output

signal

SALT

R4,

is

look

ground,
should

that

1

output

a

10

program

If

chip,

as

well

present,

chip

for

the
and

of

the

PCB
and

be

5.6

5.6.1
RS-232

The
short

4:

A
square
3
directly
change
change
Ul
current-limiting

possible

negative-going
computer
supply.
pin

RS-232

output

program,

10
20

30
square
volts

pin

15.

Output
problems

POKE
POKE
GOTO

wave

wave

positive.

at

Ul

and

PIA

12

but
to
that

Check
If

Problems

Missing

are

may

be
running

65312,2
65312,0

10

of

should
the

chip

try

U2

or
not

have

portion,

utilizes

for

it

is

or

Incorrect

just

checked

approximately

go

If

again.

look

at
resistor
a

positive-going

negative

not

it,

at

the

(Ul

for

the

the

there,

about

by

least

output

pin

If

PCB

edge

R3,

as

as

entering

and

scoping

40
3

12).
the

faults.

connector,

or

this
negative

is

voltage

proceed

easy

Hz

volts

is

not

If

output

look

output,

the

portion

C-7.5

as

in

the

the

should

negative

there,

it

is

If

check

for

only

to

the

cassette

following

output

appear.

is

still

still

the

PCB
but

circuit
of

or

better)

Power

and

look

not

output

faults.

not

the

problems.

at

J3

The

at

least

for

not

there,
there,
is

It

the

in

the

power

at

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pin

it

at

is

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Manual

flowchart.
portion
likely

5.6.2
RS-232

Ground
connect
goes
any
still

5.7

Almost

traced
modulator.
and
modulator,

low.

of

exist,

Sound

look

10

at

Input
input

pin

the

any

to

If

to

the

fault.

1

pin

1

Repeat

conditions

Problems
sound

U3.

As a

for

pin

SOUND

it

is

there,

RS-232

Problems
problems

of

J3

of

J3

then

problem

Other

quick

the

waveform

F:

200,255:GOTO

output

can

and

to

the

test

are

change

possibilities

be

insure

+5

volts

not

PIA

in

check,

shown

but

there

waveshape,

checked

that

and

with

10

U2

the

J3

met,

or

Color

key

in

in

Ul

insure

pin

replace

check

include

in

the

Figure

is

no

negative

then

a

static

pin

5

goes

that

2

and

Ul.

for

Computer

PIA

following

5-17

Ul

Ul
PCB

2
U2

at

is

most

condition.
high.

Ul

pin

pin

If

problems

faults.

can

and

program

the

4.

be

Then

5

If

the

If

the

the

modulator

the

T.V.
then
exists,

5.8
As

associated

joystick
problems.
a

joysticks

change

Joystick

with

problem.

5 CLS
10
20
30
40
50
60

70 PRINT @

80

waveform

was

check

sound

with

pots,

Of

and

A=JOYSTK(O)
B=JOYSTK(l)
C=JOYSTKC2)
D=JOYSTK(3)

E=(PEEKC65280)AND1)

F=(PEEK(65280)AND2)/2
GOTO

is

(did

turned

U3

or

U2

for

PCB

Problems
problems,

U3.

and

course,

To

test

key

in

O,A,B,C,D,F,E

10

present

you

check

up?).

as

faults.

Additional

U7,

CR7,

PCB

the

and

necessary.

joystick

joysticks,

but

to

If

and

and

execute

no

sound

see

if

the

waveform

If

problems
possibilities
CR8

for

connector

connect

the

is

heard,

the

volume
is

the

problem

are

fire
faults

two

following

not

almost
include

button

could
KNOWN

program:

replace
control
present,

still

always

U2

also
GOOD

on

for

be

----------1tad1elllaell----------

-

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c_o_1_o_r_c_o_m_p_u_t_e_r_2

The

top

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joystick.

get

each

numbers

joystick,
bottom
be

1

when

fire
button

If

results,

if
Shack
are

button

any

it

special

is
replacement

By

number

in

between.

which

two

numbers

the

and

the

of

the

replace

necessary

is

diodes

____

rotating

to

change

should

represent

fire

above

button

depressed.

right

the

to

diodes

with

TRS-BO

on

the
the

from

The

next

be

tested
is

number

testing

components

replace

of

a

low

®

screen

joystick,

the
not

(The

is

does

the

represent

0

to

two

numbers

in
two
depressed

left

the

not

discussed

CR7

or

proper

forward-voltage

you

63
the

fire

number

right

yield
CR8,

should

and

same

fire

part

Service

the

include

represent

manner.

buttons,

and

0

is

the

button.)

the

desired
above.
use

exact

number

drop.

right
be

able

all

the

and

when

left

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Radio

as

Manual

to
left

The

will

the

fire

these

5.9
In

cartridge,
using
causes
the
the
oscilloscope,

probe

should,
possibility
addressing"
device
caused

(U22)

If

should

5.10
The

the

testing
checked
defective
addition
power

frequency

flowchart

supply

cartridge

checking

a

known

the

most

edge

at

of

at
by

and

the

cartridge
be

Power

Color

unit

of

without

supply should

is

Problems

any

the

obvious

good

computer
likely
connector.

and

the

processor

course,

that
type

a

time

the

address

UlO

checked

to

to

and

Supply

Computer

work.

the

power

external

tight

noise.

for

information

"almost"

kind

cartridge.

to

cause

check

see
could
of

problem,

to

be

Ull.

does

for

2

Following

any

I/O

load

(+/-

be

Refer

functioning

of

symptom

first
lock

would

To

check
each

and

identical
cause

activated.

decoding

not

auto

opens· to

power

supply.

devices

could
5%)
relatively

to

on

dealing

step

If

up

or

be

open

this,

address

the

other

signals.

this

which

circuit

start,
the

supply

is

a

The

or

confuse

regulation

Figure

AC

content.

correctly,

is

to

a

known

execute

address

use

and

at

symptom

would

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consisting

the

connector.

must

flow

power

cartridges

free

5-3

function

chart

the
of

of

as

with

be

a
the

would

supply should

an

sure

good

random

or

dual

data

connector.

One

would

allow

lines

for

findings.

the

DC

AC

ripple

well

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the

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external
that

cartridge

garbage,

data

trace

line,

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more

most

of

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and

properly

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attached,

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power

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than

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or

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than

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quite

to

that

computer

not

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case

configuration

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be

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can

might

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work

at

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as

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the

cause

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than

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-

__

c_o_1_o_r_c_o_m_p_u_t_e_r_2

____

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Manual

Check

for
at
(End

Scope

at

Set Scope

+5VDC

Right

End

closest

+5V

right

end

mV/Div

100

Check negative
voltage at
pin

15

of

to U 1)

Source

of

for

50-

.

U1,

R2

R2.

No

No

POWER

SUPPLY

CHECK

Preliminary:
Unplug

the

probe

top

ground

the

case.

Computer
coax
output

cable

to
switchbox.
ohm

twin
switchbox
Channel
both
Plug
T.V.

3

T.V.

in

computer.

and

Computer.

Connect

lead

ground.

from

modulator

TV/Computer

Connect

lead

to
or
and

T.V.

output

4

as

modulator.

Computer.

Remove

scope

to

Connect

the

from

Select

desired

Turn

75

on

on

No

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__

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TRS-BO

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Service

Manual

Check DC Voltage

at

collector

Measure

across

of

01

DCV

R2

Check

at anodes

CR3 & CR4

POWER

AC

Voltage

of

SUPPLY

Check AC Voltage
of

CHECK

at outside

transformer

(continued)

lugs

sec

.

Replace These

Diodes

Check capacitors

PCB

for

REPAIR

shorts.

as

Recheck supply.

required

Measure

Recheck supply

at U1-1

Replace

DCV

01

Replace

Recheck supply

U1

Check AC voltage

Xfmr pri

at

Replace cord

Recheck supply

as

required

mary

or

fuse

Replace switch

Recheck

Replace

Recheck supply

supply

Xfmr

Recheck

Supply

ltadle

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lhaeli----------

86

-

Color

Computer

2

TRS-BO

®

Service

Manual

POWER

SUPPLY

CHECK

(continued)

Measure voltage at

collector

of

a 1

(case)

Replace

U1

Recheck supply

Check.cathodes

of

CR1

&CR2

for

AC

voltage

Replace

01

Recheck supply

With

'scope

determine

frequency

of

AC

component

Check Vee

pin

of

each IC

to

determine

if

IC excessively noisy

Use

'scope

'.

Check

AC

voltage

at anodes

of

CR3 &

CR4

Replace C2

Recheck supply

Replace

CS, C11,

or U1. Recheck

supply

Replace despike

capaci

tor

for

that

chip

Replace

chip

Recheck

supply

Replace chip

Recheck

supply

ltad1elhaell---------

- 87

__

.....

c_o_1_o_r__.c.o_m~p-u•t-e_r

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"T~!S-~CJ

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Ch. A -

Cathodes

of

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AC

Coupled

Ch.

B -

Anodes

of

CRl,

2

.2

V/Division

AC

Coupled

Horizontal

- 5

mSec/Div

Trigger

-

Internal,

Ch.

A

Slope

Positive

Figure

5-1.

Normal

Power

Supply

(120

Hz

Ripple)

All

settings

same

as

above.

One

transformer

lead

pulled

loose

to

simulate

open

diode.

Note

that

ripple

frequency

has

changed

from

120

Hz

to

60 Hz,

and

that

ripple

has

increased

from

approximately

1 V

p-p

to

2 v

p-p.

Although

this

computer

might

appear

to

function,

the

regula-

tor

transistor

gets

excessively

hot

and

erratic

operation

would

likely

follow.

Figure

5-2.

Power

Supply

(60

Hz

Ripple)

---------------------~ad.Olhae~-------------------

-

88

-

____

c_o_1_o_r

__

c_o_m_p_u_t_e_r

___ 2 ________

"T~!3-EICl

®

___________

s_e_r_v_1_·c_e

__

M_a

__

n_u_a_1

__

Ch.

A - +5V

Source

CU21-8)

50

mV/Division

AC

Coupled

Horizontal

-

.5µSec/Division

Trigger

-

Internal,

Ch.

A

Figure

5-3.

High

Frequency

Component

of

+5V

Source

---------------------~ad1elhae~-------------------

-

89

-

____

c_o_1_o_r

__

c_o_m~p-u_t_e_r

___ 2 ________

T'~Si-~C>

® ----------•s•e•r-v•1-·c.e.-....M-a.n.u.a.1--.

Figure

5-4.

Ch. A - E

Ch. B - Q

Horizontal

Trigger

E

and Q Clocks

Clock

(top
2V/Division
DC

Coupled

Clock

(top
2V/Division
DC

Coupled

-

.2µSec/Div.

-

Internal,

Slope

Negative

R26)

R24)

Ch.

A

Figure

5-5.

VDG

Clock

(top)

Ch.

A -

Ch. B -

Horizontal

Trigger

and

Modulator

08

pin

33
lV/Division
DC

Coupled

Modulator,
50

mV/Division

AC

Coupled

-

.2µSec/Division

-

Internal,
Slope

Negative

Clock

pin

"A"

Ch.

A

(bottom)

---------------------nad1elhaeli---------------------

-

90

-

Color

Computer

-----------TRS-BO

2

®

-----------

Service

Manual

Note
porch
the
the

This

Ch.

A - Y

Ch.

B -

Horizontal
Trigger

the

dip

time.

1372

3.58

chip
MHz

picture

CU8

pin

.2V/Division

AC

Coupled

Phase

B (U8
lV/Division
DC

Coupled

-

lOµSec/Division

-

Internal,

Slope

in

This

the

Positive

Phase

unbalances

(inside

Burst
was

Signal

taken

Figure

28)

pin

Ch.

B

the

Modulator),

for

with

5-6.

10)

A

signal

the

the

a

standard

Y

LEFT

MARGIN~

that

balanced

causing

T.V.

and

Phase

:

occurs

Modulator

green

B

BACK

PORCH
FRONT

I

~VIDEO~

PORCH

ACTIVE

during

it

to

screen.

SYNC

...

r---

1

SYNC

PEDESTAL

back

inside

generate

TIP

RIGHT

"-MARG
1

I

I

I

IN

-------------------nad1elhaell------------------

- 91 -

Color

Computer

-----------TRS-80

2

®

-----------

Ch.

A -

Ch.

B -

Horizontal
Trigger

Service

Phase

B,

.5V/Division

DC

Coupled

Phase

.

5V/Division

DC

-

A,

Coupled

-

lOµSec/Division

Internal,

Slope

Positive

Manual

U8-10

U8-ll

Ch.

A

Figure

Figu

re

5- 7 .

5-8.

Phase

Phas

Band

e B

and

A

A

Phase

Phase

Green

Screen
10
20

Relationships,

Settings

Blue

Screen

10

20

Relationships,

CLS
GOTO

same

CLS
GOTO

20

as

6

20

Green

Figure

Blue

Screen

5-7

Screen

Figure

5-9.

Phase

B

and

A Ph

ase

- 92 -

Settings

Red

Screen

10

20

Relationships,

same

CLS

GOTO

as

4

Figure

20

Red

5-7

Screen

Color

Computer

-----------TRS-BO

ARTIFACTING SIGNALS
To

check,
accomplish
to

garbage

the

this,
on

2

computer

run

the

screen):

must

the

be

in

following

®

-----------

the

High-Res

program

(pay

Service

mode.

no

attention

Manual

To

Figure

5-10.

Artifacting

Signals

10
20

Ch.

Ch.

POKE
GOTO

A - Y

B -

Horizontal
Trigger

Ch.

A - Y (U8

Ch.

B -

Horizontal
Trigger

65314,
20

CU8

pin

.2V/Division

AC

Coupled

U4

pin

6

2V/Division

DC

Coupled

-

lOµSec/Division

-

Internal,

Slope

Positive

pin

.2V/Division

AC

Coupled

U4

pin

5
2V/Division
DC

Coupled

-

lOµSec/Division

-

Internal,

Slope

Positive

24

28)

28)

Ch.

Ch.

A

A

Figure

Figure

5-11.

5-12.

Artifacting

Artifacting

-----------nad1el'haell-----------

Signals

Signals

-

93

-

Ch.

A - Y (U8

Ch.

B -

Horizontal
Trigger

pin

.2V/Division

AC

Coupled

Phase

A

CU8-ll)
lV/Division
DC

Coupled

-

lOµSec/Division

-

Internal,

Slope

Positive

28)

Ch.

A

__

c_o_1_o_r_c_o_m.-p_u_t_e_r_2

____

TRS·BO

®

_____

...

s

...

e_r

...

v_.i_.c.e.....,M-.a_n_,u_a_l_

Figure

5-13.

Address

Ch. A -

Ch.

B -

Horizontal
Trigger

Lines

A9

CU23,
2V/Division
DC

Coupled

A7

CU23,
2V/Division
DC

Coupled

-

.2µSec/Div.

-

Internal,
Slope

(typical)

Positive

pin

pin

17)

15)

Ch.

A

Figure

5-14.

Data

Ch.

A -

Ch.

B -

Horizontal

Trigger

Lines

(typical)

D2

CU23,
2V/Division
DC

Coupled

D3

(U23,

2V/Division

DC

Coupled

-

.2µSec/Division

-

Internal,

Slope

Positive

pin

pin

29)

28)

Ch.

A

-----------1tad1e

lhaell----------

-

94

-

__

c_o_1_o_r_c_o_m..;p•u-t_e_r

__ 2 ____

TRS-BO

®

_____

.;s;..;e;..;r•v•i•c•e-...M-.-a

...

n.-u.-a.1.__

Memory

Signals

Ch.

A -

RAS*

(021,

pin

4)
2V/Division
DC

Coupled

Ch.

B -

CAS*

(021,

pin

15)
2V/Division
DC

Coupled

Horizontal

-

.lµSec/Div.

Trigger

-

Internal,

Ch.

A

Slope

Negative

Figure

5-15.

RAS*

and

CAS*

Ch. A -

Data

In

(021,pin

2)
2V/Division
DC

Coupled

Ch.

B -

Data

Out

(021,

pin

14)
2V/Division
DC

Coupled

Horizontal

-

.2µSec/Division

Trigger

-

Internal,

Ch.

A

Figure

5-16.

Data

In

and

Data

Out

----------1tad1elhaeli----------

-

95

-

_.....,c_.o

... 1 ...

o_r_..c._o;..m_.p._u;;.t.;.e_r...-2

____

TRS·BO

®

_____

..

s.,.e.,.r

...

v._1

.. · c,;;;,;;;;;e.....,.M_a.n.u

.. a ..

1..__

Figure

5-17.

Sound

Ch. A -

Ch.

B -

Horizontal
Trigger

10

and

SOUND

cassette

Sound

CU3,

Out

pin
2V/Division
DC

Coupled

Cassette

CJ4,

pin
2V/Division
DC

Coupled

-

.5µSec/Div.

-

Internal,

Slope

200,

Positive

255:GOTO

Output

Out

1)

5)

Ch.

A

10

Figure

5-18.

cassette

Ch.

A -

Ch. B -

Horizontal

Trigger

Note:

nal

CJ4-5)

the

Cassette
through
capacitor.
above

zero

Crossing

Cassette

Detector
2V/Division
DC

Coupled

cassette

.5V/Division

DC

Coupled

-

-

Internal,
Slope

The

Cassette
is

a

10

The

must

be

Zero

Crossing

CUl,

Input(J4

.5µSec/Division

Ch.

B

Positive

Output

coupled

Input

µF

non-polarized

same

back

signal

program

executed.

Detector

pin

pin

sig-

to

CJ4-4)

7)

4)

as

--------------------nat11elhaell--------------------

- 96 -

Color

Computer

2 ®

Service

Manual

-----------TRS-BO

R

-----------

6/

Exploded

View/Parts

List

Contained

in

this

section

of

the

manual

is

the

exploded

view

and

parts

list

for

the

Color

Computer

2.

The

standard

BASIC

unit

is

catalog

Number

26-3026

and

does

not

contain

IC

Ul3.

Ul3

is

used

only

for

the

Extended

BASIC

version

of

the

Color

Computer

2.

The

parts

listing

for

the

main

PCB

reflects

this

difference.

Be

sure

to

specify

the

correct

board

number

if

ordering

a

complete

board

assembly.

-----------1tad1elhaell----------

-

97

-

Exploded

---------lladlOlhaell---------

View,

Color

Computer

- 98 -

2,

26-3026/7

C

olor

Computer

2 ®

Service

Manual

-----------TRS-BO

R

-----------

Parts

List,

Color

Computer

2,

#26-3026

(Standard

Basic)

or

#26-3027

(Extended

Basic)

=======================================================

Item

Qty

Description

Part

Number

=======================================================

1

2

3

4

5

6

7

8

9

10

11

12
13
14
15

16

17
18
19

20
21

22
23

1
1

4

1

1
1

1
1

3

1

6

3

2

1

2

3

6

1

1
1
1

1
1

Case,

Bottom

case,

Top

Feet,

Rubber

Door,

Cartridge

Spring,

Cartridge

Cord,

Power

Transformer,

Power

(Tl)

Fuse,

300

mA,

Slo-Blo

(Fl)

Jumper

Wire

Shield,

Bottom

RFI

Clip,

RFI

Shield

Clip,

Keyboard

Clip,

RFI

40-Pin

Connector

Keyboard

Assembly

Screw,

#6-19

x

1-1/2"

CXfmr)

Screw,

#4-19

x

5/8"

(PCB)

Screw,

#6-19

x

3/4"

(Case)

Logo,

Radio

Shack

CC2

Label,

Serial/UL

Label,

Tamper

Label,

FCC

ID

Con

26-3027

Model

only)

Label,

UL

Double

Insulated

Logic

Board

Assembly

Con

26-3027

Model

only)

8719311
8719312
8719123
8719284
8739012
8709423
8790052
8479020
8432019
8539037
8729238
8729239
8729078
8790529
8569086
8569193
8569185
8719324
8789964
8789090
8789961

or

8789100
8857625

or

8857636

----------ltadlOlhaell----------

-

99

-