Morrow MDT 50 Service Manual

MDT50

VIDEO DISPLAY TERMINAL

SERVICE

MANUAL

Copyright

(C) 1983

by

Morrow

Inc.

All

rights

reserved.

No

part

of

this

publication

may

be

reproduced,

transmitted,

transcribed,

stored

in

a

retrieval

system,

or

translated

into

any

language

or

computer

language,

in

any

form

or

by

any

means,

electronic,

mechanical,

magnetic,

optical,

chemical,

manual

or

otherwise,

without

prior

written

permission

of

Morrow

Inc.

DISCLAIMER

No

representations

or

warranties,

express

or

implied,

are

made

with

respect

to

the

contents

hereof,

including,

but

not

limited

to,

the

implied

warranty

of

merchantability

or

fitness

for

a

particular

purpose.

Further,

Morrow

Inc.,

reserves

the

right

to

revise

this

publication

and

to

make

changes

from

time

to

time

in

the

content

hereof

without

obligation

to

notify

any

person

of

such

revision.

Morrow
600 McCormick

St.

San

Leandro,

CA

94577

TABLE

OF

CONTENTS

SECTION

o

--

INTRODUCTION

Scope

of

this

Manual
WARNING
Components

Block

Diagram

Interconnections

Theory

of

Operation

Terminal

Operation

Data

Paths

Quick

Check-out

1

--

THE

VIDEO

BOARD

Theory

of

Operation

Video

Signal

Vertical

Synch

Horizontal

Synch

Miscellaneous

Controls

Troubleshooting

Components

Test

Points,

Typical

Waveforms

&

Signal

Levels

2

--

THE

MAIN LOGIC

BOARD

Theory

of

Operation

Test

Points,

Typical

Waveforms

&

Signal

Levels

3

--

THE

KEYBOARD

Theory

of

Operation

Test

Points,

Typical

Waveforms

&

Signal

Levels

4

--

THE

POWER

SUPPLY

Theory

of

Operation

Troubleshooting

Components
Test

Points,

Typical

Waveforms

&

Signal

Levels

PAGri

INT-l
INT-l
INT-l
INT-3
INT-4
INT-5
INT-5
INT-6
INT-7

VI})-l

VID-l

VID-l
VID-l

VID-;l
VID-;l

VID-2

VID-6

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KYB-l

KYB-l

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PWR-l
PWR-l

PWR-3

5

--

MAINTENANCE

The

Monitor

Unit
General
Replacing

the

CRT

tube

The

Keyboard

Unit

MTC-l

MTC-l
MT<.;-l
MTC-2

Introduction

Scope

of

this

Manual

IRnODUCTIOB

Page

INT-l

This

Manual

presents

details

of

the

circuitry

and

data

paths

of

the

Morrow

MDT50

Video

Display

Terminal)

along

with

information

on

typical

wave-

forms

and

signal

levels,

to

allow

service

personnel

to

troubleshoot

and

repair

the

terminal,

as

needed.

Familiarity

with

the

Morrow

MDT50·

User's

Manual

is

assumed.

While

every

effort

has

been

made

to

assure

that

the

information

contained

herein

is

accurate

and up

to

date)

Morrow

Designs,

Inc.

reserves

the

right

to

make

engineering

changes

and

appropriate

parts

substitutions

without

prior

notice

in

the

interests

of

increased

and

improved

performance.

> > > >

WARRING

< < < <

CRITICAL

COMPORDT

WARBlRG:

SERVICEMAR

WARRING:

This

product

contains

components

which

are

critical

for

X-Radiation

Safety.

See

Service

Manual

for

proper

replacement.

Normal 2nd Anode

Voltage

is

12

KV

at

Zero beam

current,

AC

120V

input,

and must

lOT

exceed

13

KV

under

any

operating

conditions.

To

measure

2nd Anode

Voltage,

use

High Impedance

meter.

Connect

(-)

to

chassis,

use

a High

Voltage

lead

from

(+)

to

2nd Anode.

Components

of

the

Morrow

MDTSO

Terminal
External
From

an

outside

viewpoint)

the

Morrow

MDTSOconsists

of

two

units:

The

Monitor

Unit,

containing

the

CRT)

power

supply)

and

control

circuits;

and

the

Keyboard

Unit,

containing

the

physical

keyboard)

its

decoding

circuitry,

and

circuits

for

communicating

with

the

Monitor

Unit.

The

Keyboard

and

Monitor

Units

are

connected

by

a

coiled

telephone

handset

cord

with

7,62

mm

(0.3

in)

male

plugs

at

each

end. Power

is

supplied

via

a

3-wire

grounded

cord,

terminated

by a

U.S.

NEMA

standard

plug

(which

may

be

replaced

to

suit

local

power

system

requirements).

Communications

with

a Host

computer

or

modem

and a

printer

are

provided

via

asynchronous

RS-232

communication

via

two

female

DB-25

receptacles

on

the

rear

of

the

Monitor

Unit.

Controls

are

provided

on

the

Monitor

Unit

for

Power

ON/OFF,

Contrast,

and

setting

operating

parameters.

Introduction

Internal
Internally,

the

Morrow

MDT50

consists

of:

Page INT-2

~

A

Transformer

and

Voltage

Selector

Switch

for

converting

115V

or

230V

AC

mains

power

to

10.5V

AC,

16.7V

AC,

and

21.3V

AC.

~

A Power

Supply

board,

with

rectifiers

and

voltage

regulators,

to

pro-

duce

+5V,

+15V,

and

-12V

DC

[regulated

to

±IO%].

~

A Main

Logic

Board,

with

a 68A02

Microprocessor,

16k

of

EPROM-resident

firmware,

2k

of

character

storage

RAM,

4k

of

attribute

and

control

storage

RAM,

a 68A45

CRT

Controller,

a 68A21

PIA,

one

6850

and

two

6851

ACIAs

for

Keyboard,

Host

and

Printer

communications,

respectively,

as

well

as

miscel-

laneous

control

and

sequencing

logic.

~

A Video

Control

board,

to

convert

Horizontal

and

Vertical

synch

pulses

to

the

proper

waveforms

for

controlling

CRT

raster

scan,

and

circuitry

to

control

pixel

display.

Connection

is

made

via

cables

to

a

12"

diagonal

CE745129

VRA

tube

(or

equivalent)

for

actual

display.

~

A

small

Contrast

control

and

connector

board,

having

a

rotating

poten-

tiometer

for

contrast

control,

and a

female·

RJ-ll

receptacle

for

the

Keyboard

connector

cord.

~

A

Keyboard,

with

a

93-key

switch-matrix

keyboard,

decoded

by

an

8035

stand-alone

microcomputer,

which

generates

RS-232

signals

by

toggling

one

output

line

under

the

control

of

on-chip

software,

and

receives

RS-232

data

via

software

use

of

interrupts.

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Introduction

Theory

of

Operation

Terminal

Operation

Page

INT-S

The

Morrow

MDT50

CRT

Terminal

is

designed

to

be

an

inexpensive

and

convenient

data-entry

and

console

device

for

a

wide

range

of

computer

and

data

applications.

The

Morrow

MDT50

will

normally

be

connected

toaHost

computer

system,

either

directly

or

via

MODEM,

by

asynchronous

RS-232

or

20ma

current

loop,

through

the

Host

connector

on

the

rear

of

the

Monitor

Unit.

The

terminal's

on-board

firmware

allows

it

to

communicate

with

the

Host

in

Full

or

Half

Duplex,

or

strictly

Local

mode

(no

outside

communication).

Communication

rates

range

from

110

to

19,200

baud.

A

subsidiary

Printer

port,

also

located

on

the

rear

of

the

Monitor

Unit,

allows

the

Morrow

MDT50

to

be

connected

to

any

ASCII

printer

with

an

RS-232

serial

interface.

Baud

rates

from

100

to

19,200

are

available.

The

terminal

provides

two

basic

modes

for

printer

operation:

Simultaneous

Mode

--

all

characters

transmitted

from

the

Host

are

displayed

on

the

monitor,

and

also

sent

to

the

Printer

Buffer

Mode

--

characters

from

the

Host

are

buffered

internally

in

the

Morrow

MDT50)

and

sent

to

the

Printer

without

being

displayed

on

the

monitor

The Morrow

MDT50"s

16k

of

on-board

firmware

provides

93

basic

commands,

as

well

as

numerous

options,

for

setting

operating

parameters.

These

commands

can

be

sent

by

the

operator

from

the

Keyboard,

or

by

the

Host

through

the

Host

port.

The commands and

their

effects

are

documented

in

the

Morrow

MDT50

User's

Manual.

Introduction

Data

Paths

Page INT-6

The Morrow

MDT50"'s

Main

Logic

Board

receives

serial

Asynchronous

RS-232C

character

data

from

either

the

Host

Port

or

the

Keyboard.

This

character

data

is

stored

ina2k-byte

Display

RAM.

Character

data

from

the

display

RAM

is

sent

continuously

to

the

Video

display

circuitry,

where

it

is

processed

by

a

Character

generating

ROM,

combined

with

attribute

data

fromaseparate

2k-byte

Attribute

RAM,

and

sent

to

the

CRT

for

display.

If

the

MorrowMDT50

is

in

Full

Duplex

Mode,

all

character

data

received

from

the

keyboard

is

immediately

transmitted

to

the

Host

hrough

the

Host

Port,

but

is

not

displayed

on

the

CRT.

If

it

is

in

Half

Duplex

Mode,

character

data

received

from

the

keyboard

is

displayed

on

the

CRT

in

addition

to

being

transmitted

to

the

Host.

In

either

Mode,

XON/XOFF

protocols

are

used

in

communicating

with

the

Host.

If

it

is

in

Simultaneous

(Transparent)

Print

Mode,

character

data

received

from

either

the

Host

or

the

Keyboard

is

displayed

on

the

CRT

and

transmitted

to

the

Printer

Port.

If

it

is

in

Buffered

Print

Mode,

character

data

received

from

the

Host

is

transmitted

directly

to

the

Printer

Port

(with

XON/XOFF

handshaking)

without

being

displayed

on

the

CRT.

Introduction

Quick

Check-out

Page INT-7

To

check

out

the

operation

of

the

Morrow

MDTSO

quickly,

and

isolate

problems:

1)

Check

for

11SV

AC

or

230V

AC

on

the

primary

(input)

leads

of

the

Power

Transformer.

a)

If

found,

go

to

Step

3.

b)

Check

the

fuse,

power

switch,

and

power

select

switch.

2)

Check

the

secondary

(output)

leads

for

10.6V

AC

on

blue,

2l.3V

AC

on

white,

and 16.7V

AC

on brown.

a)

If

OK,

go

to

Step

2.

b)

Replace

power

transformer.

3)

B204) .

Disconnect

cable

from

Power

Supply

to

Main

Logic

Board

(B404

<-->

Check

B404

for:

Pin

1

Pin

2

Pin

3

Pins

4 & S

-12V

DC

±.O.SV

+1SV

DC

±.O.

5V

+SV

DC

±.O.2SV

Ground

step

5.

a)

If

OK,

replace

cable

to

Main

Logic

Board (B404

<-->

B204).

Go

to

4)

Disconnect

cable

to

power

transistors

(B406,

407).

Check

connectors

for:

B406

Pin

1

IS.IV

DC

Pin

2

29.8V

DC

Pin

3

29.9V

DC

B407

Pin

1

5.IV

DC

Pin

2

I4.3V

DC

Pin

3

I4.4V

DC

a)

If

OK,

check

U40I

through

U403

and

capacitor.

b)

Check

Bridge

Rectifiers

BR40I,

BR402, BR403,

and

transistors

Q401

and Q403.

5)

Check

voltage

on B404

again.

a)

If

OK,

go

to

Step

7.

6)

Check Power

Transistor

voltages:

Q402

Base
Collector

-

Emitter

IO.6V

DC

5.1VDC

Il.4V

DC

Introduction

Q404

Base
Collector

-

Emitter

24.6V

DC

1S.IV

DC

2S.2V

DC

Page INT-8

7)

B104).

a)

If

OK,

check

U401

through

U403

and

capacitor.

b)

Replace

transistor(s).

Disconnect

cable

from

Main

Logic

Board

to

Video

Board

(B203

<-->

Check

signal

levels

and

typical

waveforms on

Connector

B203.

a)

If

OK,

reconnect

cable

(B203

<-->

B104)

and

run

Monitor

Check

Subroutine

(hit

ESC

M on

keyboard)

for

software

problems.

Check/replace

ROMs,

if

necessary.

b)

Go

to

Step

8.

8)

Disconnect

cable

to

Contrast

Board

(B208

<-->

B508).

Check

signal

levels

and

typical

waveforms on

Connector

B208.

a)

If

OK,

Reconnect

cable

to

Contrast

Board (B208

<-->

B508), go

to

Step

9.
b)

Check

all

test

points

on

Main

Logic

Board

for

proper

signal

levels

and

typical

waveforms,

then

isolate

and

replace

defective

parts.

9)

B309).

Disconnect

cable

connecting

Keyboard

to

Contrast

Board

(B509

<-->

Check

Contrast

Board

for

defective

parts

and

broken

traces.

a)

If

OK,

reconnect

cable

to

Keyboard

connector

(B509

<-->

B309)

and go

to

Step

10.

b)

Replace

Contrast

Board.

10)

Check

signal

levels

and

typical

waveforms

at

B309

on

Keyboard

PC

board.

a)

If

OK,

check

all

test

points

on

Keyboard

for

signal

levels

and

typical

waveforms.

Isolate

and

replace

defective

components.

b)

Replace

coiled

telephone

handset

cord.

11)

END.