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EK-VT420-PS-002

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Document:	VT420 Service Guide
Order Number:	EK-VT420-PS
Revision:	002
Pages:	82
Original Filename:	http://bitsavers.org/pdf/dec/terminal/vt420/EK-VT420-PS-002_VT420_Service_Guide_199201.pdf

OCR Text

VT420 Service Guide
Order Number EK-VT420-PS-002

···-----·'"···········..

Digital Equipment Corporation

First Edition, December 1989
Second Edition, January 1992
The information in this document is subject to change without notice and should not
be construed as a commitment by Digital Equipment Corporation. Digital Equipment
Corporation assumes no responsibility for any errors that may appear in this document.
The software described in this document is furnished under a license and may be used or
copied only in accordance with the terms of such license.
No responsibility is assumed for the use or reliability of software on equipment that is not
supplied by Digital Equipment Corporation or its affiliated companies.
Restricted Rights: Use, duplication, or disclosure by the U. S. Government is subject to
restrictions as set forth in subparagraph ( c) ( 1 ) ( ii ) of the Rights in Technical Data and
Computer Software clause at DFARS 252.227-7013.
Copyright e Digital Equipment Corporation 1989, 1992
All Rights Reserved.
Printed in U.S.A.

The following are trademarks of Digital Equipment Corporation:

SSU, VMS, VT, VT52, VTlOO, VT220, VT320, VT420, and the DIGITAL logo.
ADP is a trademark of Automatic Data Processing, Inc.

Kodak is a registered trademark of Eastman Kodak Co.
OLIVE'l'TI is a registered trademark of Ing. C. Olivetti & C.,·S.p.A.
UNIX is a registered trademarlt of UNIX System Laboratories, Inc.

This document was prepared and published by Educational Services Development and
Publishing, Digital Equipment Corporation.

Contents
About This Guide
1
1.1
1.2

Vll

VT420 Models and Features
VT420 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VT420 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1
1

Troubleshooting and Testing

Troubleshooting .................................. .
2.1
VT420 Self-Tests ................................. .
2.2
Before You Start ................................ .
2.2.1
2.2.2
How to Type an Escape Character .................. .
Power-Up Self-Test .............................. .
2.2.3
DEC-423 Port Loopback Test (6-Pin) ................ .
2.2.4
RS-232 Port Data Lines Loopback Test
2.2.5
(25-Pin, Worldwide Model Only) ................... .
RS-232 Port Control Lines Loopback Test
2.2.6
(25-Pin, Worldwide Model Only) ................... .
Printer Port Loopback Test (6-Pin) .................. .
2.2.7
2.2.8
Screen Alignment Test ........................... .
Printer Problems ................................. .
2.3
Error Codes ..................................... .
2.4

10
11
11

13
14
16
17
18
18
19
20

iii

iv Contents

Removing and Replacing FRUs

3.1
3.2
3.3
3.4
3.5

Top Cover........................................
CRT/Yoke/Bezel Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . .
Terminal Board Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CRT Disposal (Digital Service Representatives Only) . . . . . .

Adjusting The Video Monitor

4.1
Aligning the Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Monitor Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.1
Before You Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.2
Displaying the Screen Test Pattern . . . . . . . . . . . . . . . . . .
4.2.3
Screen Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Subcontrast ................................... .
4.2.4
Rotation ...................................... .
4.2.5
Horizontal Width ............................... .
4.2.6
4.2.7
Vertical Height ................................. .
Vertical Linearity ............................... .
4.2.8
Centering ..................................... .
4.2.9
4.2.10 Focus ........................................ .

Using Set-Up

5.1
5.2
5.3
5.4

Displaying Set-Up Screens. . . . . . . . . . . . . . . . . . . . . . . . . . .
Changing Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Saving Set-Up Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recalling Set-Up Values.............................

Modems, Cables, and Documentation

A.1
A.2
A.3

Modems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22
26
34
36
38

42
45
46
46
47
47
47
49
49
49
50
50

51
53
53
53

54
54
57

Contents

VT420 Recommended Spares

B.1
B.2
B.3

VT420 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recommended Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical/Functional Diagrams

58
60
61

Index
Figures
2-1
2-2
4-1
4-2
4-3

VT420 Video Terminal with Keyboards . . . . . . . . . . . . . . . . .
VT420 Rear Connector Panel and Loopback Connectors . . . .
Set-Up Directory Screens. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Screen Align Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Monitor Adjustment Controls . . . . . . . . . . . . . . . . . . . . . . . . .
4-4 Screen Test Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-5 Rotation and Centering Adjustment. . . . . . . . . . . . . . . . . . . .
5-1 Set-Up Directory Screens... . . . . . . . . . . . . . . . . . . . . . . . . .
A-1 VT420 Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C-1 VT420 North American Model . . . . . . . . . . . . . . . . . . . . . . . .
C-2 VT420 Worldwide Models . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5
15
43
44
45
46
48
52
56
64
66

Tables
1-1
2-1
2-2
2-3

VT420 Model Differences... . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting the VT420 . . . . . . . . . . . . . . . . . . . . . . . . . .
VT420 Self-Test Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VT420 Display Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . .

3
6
12
20

This guide describes how to service the VT420 monochrome video
terminal. The guide is for Digital's service personnel.
The guide has five chapters that cover the following topics:
VT420 models and features
Troubleshooting and testing
Removing and replacing field replaceable units (FRUs)
Adjusting the video monitor
Using set-up
Appendices provide information on the following topics:
Modems, cables, and related documentation
VT420 models and recommended spares
Physical/functional diagrams

Tools Required
You need the following tools to service the VT420 video terminal:
Tool

Part Number

Anode discharge t.ool

29-24 717 -00

25-pin, RS-232 EIA loopback connector

12-15336-00

Metric measuring tape

29-25342-00

Two 6-pin, DEC-423 loopback connectors (modular jack)

12-25083-01

Phillips screwdriver, number 2

29-11005-00

Tuning wand

29-23189-00

Video alignment tool

29-26128-00

vii

viii

About This Guide

Conventions
The following conventions are used in this guide:
Warnings

Provide information to prevent personal injury.

Cautions

Provide information to prevent damage to equipment.

Notes

Provide general operating information.

Set-up features

The names of set-up features appear in bold type.
Example: Use the save feature in the Set-Up Directory
screen.
Set-up feature settings and fields appear in this type.
These are the settings that appear on the screen.
Example: Select the Screen Align field.

ANSI keyboard keys
(LK401 or LK421)

Appear as normal text in a~

PC keyboard keys
(LK443 or LK444)

Appear as bold text in a§!.

ANSI keys (with PC
keys)

When a PC (LK.4431LK444) command sequence differs
from an ANSI (LK.401/LK421) command sequence, the
PC key sequence appears in parentheses after the ANSI
key sequence.

Example: Press the IRetum I key.
Example: Press the

la.turn Ikey.

Example: Press the IRetum Ikey 4Enter~.
RS-232

Used to represent electrical standard EIA 232-D, which
replaces electrical standard RS-232-C.

This is an abbreviation for part number.

1.1 VT420 Models
The VT420 is a monochrome text terminal that provides all VT320
features plus enhancements. The VT420 has a 359 mm (14-inch) diagonal
monitor with a flat, antiglare screen. The monitor can display 24, 25, 36,
or 48 lines of text in an 80- or 132-column format. The last line of each
session is reserved for a status line. An attachable tilt-swivel base lets
the user adjust the viewing angle for optimum comfort.
There are three models of the VT420 video terminal:
•

North American (VT mode)

•

Worldwide (VT mode)

•

Worldwide (VT mode and PC TERM mode)

The worldwide models come in two versions, standard and low-emission.

1.2 VT420 Features
The following list includes the features that are common to the North
American and model and two worldwide models. Table 1-1 lists the
differences between the three models. The worldwide model with PC
TERM mode can use the standard ANSI (LK401), short ANSI (LK421),
or PC (LK443/LK444) keyboard. See Installing and Using the VT420
Video Terminal with PC Terminal Mode for details on the features of the
different keyboards.

2 VT420 Models and Features

Common Features
•

Two-session capability

•

Local copy and paste feature

•

Off-screen page memory

•

Ability to display 24, 25, 36, or 48 lines/screen

•

Screen centering capability

•

Screen overscan

•

FCC Class A compliance

•

Two 6-pin, DEC-423 connectors (One is for the primary host port, and
one is for the secondary host or printer port. Both have DEC-423 local
direct-connect capability.)

•

Asynchronous communication up to 38.4K bits/second

•

Four operating modes:
VT400 mode, 7-bit controls (default)
VT400 mode, 8-bit controls
VTlOO mode
VT52 mode

•

Ability to store macros

•

One full-screen window or two horizontal split-screen windows

•

Screen saver

•

Character sets:
U.S. ASCII
DEC Supplemental Graphic
ISO Latin Alphabet No. 1
ISO Latin-1 Supplemental
DEC Special Graphic
DEC Technical
Downloadable character set

•

Terminal status line

•

Keyboard indicator on the last line of the screen

•

Ability to disable or enable keys E.!I through ~

•

Extended keyboard reports

VT420 Models and Features

•

LK401 keyboard that includes
Right and left I Alt Function I keys
Right I Compose Character I key
Lock and Hold LEDs

Table 1-1

VT420 Model Differences

Features

FCC Class B compliance

Yes

Attached

Yes

Detachable with country-specific plug

Yes

120 V at 60 Hz only

Yes

100 V to 240 V (autoselect) at 50 Hz or 60 Hz

Yes

One 25-pin, RS-232 connector for the primary host, with
modem control

Yes

Screen rotation capability

Yes

National replacement character sets

Yes

Two Group Shift keys on the German LK401 keyboard to
replace the Compose Character keys

Yes

PC TERM mode

Yes

PC character sets

Yes

PC keyboard with 101 or 102 keys (LK443/LK444)

Yes

Short ANSI (UNIX style) keyboard with 74 keys (LK421)

Yes

Support for XPC communications protocol•

Yes

Driver support for the terminal in appropriate operating
systems

Yes

AC power cord:

Power supply ac input and line frequency:

•Refers to the remapping ofXON and XOFF points in PC TERM mode. After remapping,
XON is 65 1s and XOFF is 671&·
NA = North American model with VT mode.
WW = worldwide model with VT mode.
PC = worldwide model with VT mode and PC TERM mode.

This chapter explains how to troubleshoot general problems on the VT420
terminal. The chapter also describes how to run the self-tests built into
the terminal and lists error codes for the tests.

2.1 Troubleshooting
Table 2-1 lists probable causes and solutions for general problems with
the terminal.
When you turn on the VT420 terminal, it performs a power-up self-test to
check for problems. If the test finds an error, the terminal may display an
error message at the upper-left comer of the screen (Section 2.4).
During the test, the LED indicators on the keyboard (Figure 2-1) flash on
and off. If the test is successful:
•

The keyboard makes one bell tone.

•

The keyboard LEDs turn off.

•

A VT420 OK message appears on the screen.

For details on the power-up self-test, see Section 2.2.3.
The worldwide model with PC TERM mode can use the standard ANSI
CLK401), short ANSI (LK421), or PC (LK443/LK444) keyboard. See
Installing and Using the VT420 Video 'lerminal with PC 'lerminal Mode
for details on the features of the different keyboards.

Troubleshooting and Testing

•

•
Figure 2-1

VT420 Video Tenninal with Keyboards

0 ANSI (LK401/LK402) keyboard
•

Short ANSI (LK421, UNIX style) keyboard

0 PC (LK443/LK444) keyboard

U.011GS·TMI

6 Troubleshooting and Testing

Table 2-1

Troubleshooting the VT420

Symptom

Probable Cause

Solution•

Problems at Power-Up
Nothing appears
on the screen.

'Thrminal board.

The VT420 OK
display appears
and the bell tone
sounds, but the
VT420 cannot
communicate with
host.

The terminal was
powered down
with sessions
enabled.

When power is restored to the
terminal, press F4

VT420
communication
port cable is loose.

Check the cable connection on the
rear of terminal.

Baud rate is
incorrect.

Check the transmit and receive
speeds in the Communications
Set-Up screen.

The on-line/local
feature is set to

Change the feature setting to On
Line in the Global Set-Up screen.

1. Make sure all connectors on

the board are seated properly.
2. Replace the terminal board (3.3).

(lAltl Scroll Lock

Local.

Continuous bell
sound at power
up.
The bell tone does
not sound, but
VT420 OK appears
on the screen.

Communication
port circuits are
faulty.

Run the RS-232 or DEC-423
loopback tests (2.2.4, 2.2.5, 2.2.6).

'Thrminal board.

Replace the terminal board (3.3).

An object is
resting on the
keyboard

Remove all objects from the
keyboard.

Keyboard.

Replace the keyboard (3.4).

Keyboard speaker
transducer

Replace the keyboard (3.4).

• Section numbers follow the solution.

Troubleshooting and Testing

Table 2-1 (Cont.) Troubleshooting the VT420
Symptom

Probable Cause

Solution"

Screen Display Problems
Screen is off
center or rotated.

A horizontal
or vertical line
appears on the
screen.

The screen
display is
distorted or
jittery.

The screen
display does not
scroll. The hold
indicator is on.

There is
interference from
electromagnetic
energy.

Adjust the screen by using the
Screen Align field in the Set-Up
Directory screen. On worldwide
models, you can also adjust the
screen rotation.

'Turminal board.

Replace the terminal board (3.3).

CRT yoke harness
connector

Check and reconnect the connector
(3.2).

'Turminal board.

Replace the terminal board (3.3).

CRT/yoke/bezel
assembly.

Replace the CRT/yoke/bezel
assembly (3.2).

There is electrical
interference from
nearby devices.

Move the terminal away from nearby
electrical devices.

The monitor is out
of alignment

Adjust the monitor (Chapter 4).

'Turminal board.

Replace the terminal board (3.3).

Replace the
CRT/yoke/bezel
assembly

Replace the CRT/yoke/bezel
assembly (3.2).

The~

Press ~ Scroll Lock
resume scrolling.

(I Scroll Lock ~

I) to

key was pressed.

The terminal
appears locked
and does not
respond to data
from the host.

• Section numbers follow the solution.

In the Set-Up Directory:
1.

Select Clear Comm to clear the
terminal.

Select Reset to reset the
terminal.

8 Troubleshooting and Testing

Table 2-1 (Cont.)

Troubleshooting the VT420

Symptom

Probable Cause

Solution•

Screen Display Problems
The screen is
blank, except for
the blinking block
cursor in the
lower-right corner.
The screen has
been inactive for
one-half hour.

CRT saver feature
is activated.

Press any key to restore the screen
display.

Phosphor retains
an imprint of
characters on the
screen when the
monitor is turned
off.

CRT/yoke/bezel
assembly.

Replace the CRT/yoke/bezel
assembly (3.2).

Character Display Problems
In local mode,
the screen
displays different
characters than
those typed.

Alternate
character set
selected.

Clear by selecting the Reset field in
the Set-Up Directory.

Worldwide only:
Wrong keyboard
language selected.

Check the keyboard language
feature in the Set-Up Directory.

Keyboard.

Replace the keyboard (3.4).

'Turminal board.

Replace the terminal board (3.3).

• Section numbers follow the solution.

Troubleshooting and Testing

Table 2-1 (Cont.) Troubleshooting the VT420
Symptom

Probable Cause

Solution*

Character Display Problems
While on-line
with the host,
the screen
displays different
characters than
those typed. (The
terminal works in
local mode.)

Incorrect transmit
and receive
speeds.
Incorrect bits
per character or
parity setting.
Stop bits setting
is incorrect.

Set the speeds to match the host, in
the Communications Set-Up screen.
Set the data bits/parity feature
to match the host, in the
Communications Set-Up screen.
Set the stop bits feature to match
the host, in the Communications
Set-Up screen.
Replace the terminal board (3.3).

'Turminal board.
When using the
copy and paste
feature, the
pasted characters
do not match
the characters
selected. (VMS
environment)

Transmit speed
is set to 19200
baud, causing
the terminal to
send characters
faster than the
host computer can
receive them.

Using the VMS operating system,
type the following command at the $
prompt: SET TERMINAL/HOSTSYNC

Messages are
garbled and
reverse question
marks appear on
the screen.

Baud rate is
incorrect.

Check the transmit and receive
speeds in the Communications
Set-Up screen.

XON/XOFF flow
control is not
enabled.

Enable XON/XOFF fl.ow control
with the XOFF feature in the
Communications Set-Up screen.

'Turminal board.

Replace the terminal board (3.3).

Incorrect mode
settings

Select Local in the Global Set-Up
screen. Select VTlOO Mode in the
General Set-Up screen.

Other Problems

IF11I ( IEscl) does
not work when
running self-tests.

• Section numbers follow the solution.

1O Troubleshooting and Testing

Table 2-1 (Cont.) Troubleshooting the VT420
Probable Cause

Solution•

After powerup, one or more
keyboard LEDs
stay on. Or,
the LEDs do
not go through
their power-up
sequence.

Keyboard.

Replace the keyboard (3.4).

'Turminal board.

Replace the terminal board (3.3).

The set-up cursor
does not appear.

'Turminal board.

Replace the terminal board (3.3).

When using a
modem, the
modem speed
select signals do
not work.

Cables.

Check all cables and cable
connections. Replace the terminal
board (3.3).

Symptom
Other Problems

Worldwide
model: In PC
TERM mode, a
modem does not
work with the
terminal.

'Turminal board.

The modem's XON
/XOFF settings
are incompatible
with the terminal.

Use a modem with compatible XON
/XOFF settings. In PC TERM mode,
the terminal's XON point is 65 1s
characters, and the XOFF point is
6716 characters.

• Section numbers follow the solution.

2.2 VT420 Self-Tests
The VT420 has a series of self-tests to determine if the terminal board
is the faulty field replaceable unit (FRU). You can run each test from the
keyboard by entering the escape sequence for the test. Table 2-2 lists the
tests and their escape sequences.
If a test indicates the terminal board is faulty, refer to
•

Chapter 4, to adjust the components on the board, or

•

Chapter 3, to replace the board

After making adjustments or replacing the terminal board, repeat the
tests in this chapter to ensure the terminal operates correctly.

Troubleshooting and Testing

2.2.1 Before You Start
Before you run any self-test, you must either
•

Install the appropriate loopback connector on the communication port,
or

•

Set the terminal to local mode

You should save the current settings in set-up before you run tests. If you
are unfamiliar with set-up, see 5, "Using Set-Up".
•

Use the arrow keys to move the cursor in all set-up screens.

•

The IEnter I and IReturn I keys perform the same function in all set-up
screens.

To set the terminal to local mode:
1.

Press~ (jA1tlls.topj) to enter set-up. The Set-Up Directory screen

appears.
2. Move the cursor to the Global field. Press !Enter~ The Global Set-Up
screen appears.
3. Move the cursor to the on Line field. Press the !Enter! key to change
the setting to Local.
4. Press~ ( IAltlls.Jopl) to leave set-up. You do not need to save the
settings because t ey take effect when you exit set-up.
Remember to return the set-up features to their original settings after
testing.

2.2.2 How to Type an Escape Character
PC (LK443/LK444) Keyboard Only

Use the IEscl key.
All Keyboard Models

There are three ways to type an escape (ESC) character:
•

Press !Ctrll [O

•

Press !Ctrll @]

12 Troubleshooting and Testing

•

Set the terminal to VTlOO Mode in the General Set-Up screen. In
VTlOO mode, you can press IF11I to generate an ESC character. See
Chapter 5 for a description on using set-up.

Table 2-2 VT420 Self-Test Chart
Self-Test

Prerequisites

Sequence•

Power-up

None

Tum the
terminal on.

Set-up
- Local mode

Once:
ESC[4;ly
Continuously:
ESC[4;1;9y

RS-232 port data lines
loopbackt

RS-232 loopback connector

Once:
ESC[4;2y
Continuously:
ESC[4;2;9y

RS-232 port control lines
loopbackt

RS-232 loopback connector

Once:
ESCC4;6y
Continuously:
ESC[4;6;9y

Printer port loopback

DEC-423 port loopback
connector

Once:
ESCC4;3y
Continuously:
ESC[4;3;9y

DEC-423 port loopback

DEC-423 port loopback
connector

Once:
ESC[4;7y
Continuously:
ESC[4;7;9y

Screen alignment pattern

Set-up
-Local mode

ESC

Run all above tests, except
screen alignment pattern.

See individual tests. All
loopback connectors must be
connected.

Once:
ESC[4;0y
Continuously:
ESC[4;0;9y

Selected while the
VT420 is operating.

• Do not type spaces between the characters in any escape (ESC) sequence. The sequences
are shown with spaces for clarity only.

t Worldwide models only.

Troubleshooting and Testing

2.2.3 Power-Up Self-Test
This test runs automatically each time you turn on the terminal. The
test checks the terminal's internal memory, keyboard, and video circuitry.
The test also checks the communication and printer ports to see if they
are operating correctly. The individual loopback tests perform a more
complete test of each port.
You can also run the power-up self-test manually while the terminal is
operating, as follows:
NOTE

After you run the power-up self-test, all the set-up features are
automatically set to their saved values.
1.

Set up the terminal (Sections 2.2.1 and 2.2.2).

2. Type one of the following DECTST sequences:
ESC [ 4 ; 1 y
Runs the test once.
ESC [ 4 ; 1 ; 9 y
Runs the test continuously.
While the test is running:

A Wait message appears in the upper-left comer of the screen. The Wait
message may disappear at times, but it reappears until the test detects
an error or the terminal's power is turned off.
NOTE

The DECTST control function causes a disconnect. Do not use
DECTST when the connection is made through a modem.
If the test is successful:
1. The keyboard's LED indicators tum off.

2. The keyboard makes a bell tone.
3. A VT420 OK message appears on the screen. This message disappears
when any of the following events occur:
•

The terminal receives any character except XON, XOFF, or NUL.

•

You press any key.

•

You leave the terminal on and inactive for 30 minutes.

14 Troubleshooting and Testing

If the test finds an error:

If possible, the terminal displays an error message at the upper-left corner

of the screen. Each error message starts on a new line at the left margin
of the display. Table 2-3 describes these error messages.
The error messages disappear when the terminal receives any character
(except XON) or when you type any key. In local mode, the terminal
ignores characters from the host, so error messages are not affected.

2.2.4 DEC-423 Port Loopback Test (6-Pin)
For this test, connect the DEC-423 port transmit and receive data lines
together with a loopback connector (Figure 2-2). The terminal sends a
predefined set of characters on its transmit line and receives them on
its receive line. Then the terminal compares the output characters to the
input characters. If the characters do no match, an error message appears
on the screen.
To run the test:

Use a DEC-423 loopback connector, PN 12-25083-01.
1. Set up the terminal (Sections 2.2.1 and 2.2.2).
2. Connect the loopback connector to the 6-pin DEC-423 port.
3. Type one of the following sequences:
ESC [ 4 ; 7 y
Runs the test once.
ESC [ 4 ; 7 ; 9 y
Runs the test continuously.
NOTE

The continuously running test ends only if an error occurs or you
turn off the terminal. The keyboard does not make a bell tone
during this test.
If the test Is successful:

1. The keyboard makes a bell tone.
2. The keyboard's LED indicators are off.
3. A VT420 OK message appears on the screen.

Troubleshooting and Testing

If the test finds an error:

The screen displays the following message. See Table 2-3.
VT420 DEC-423 Port Error -- 5

Worldwide

Comm2 Port
6-Pin, DEC-423
Connector
(Also, Printer Port)

Power
Receptacle

North American

Comm2 Port
6-Pin. DEC-423
Connector
(Also, Printer Port)

Comm1 Port
6-Pin, DEC-423
Connector

Power
Cord

Loopback Connectors
~

6-Pin

~ (12-25083-01)

From
Pin

To
Pin

2
4

From
Pin

To
Pin

22
17

4
GSF_1448_89.DG

Figure 2-2

VT420 Rear Connector Panel and Loopback Connectors

16 Troubleshooting and Testing

2.2.5 RS-232 Port Data Lines Loopback Test
(25-Pin, Worldwide Model Only)
For this test, you connect the RS-232 port transmit and receive data lines
together with a loopback connector (Figure 2-2). The terminal sends a
predefined set of characters on its transmit line and receives them on
its receive line. Then the terminal compares the output characters to the
input characters. If the characters do no match, an error message appears
on the screen.
To run the test:

Use an RS-232 loopback connector, PN 12-15336-00.
1.

Set up the terminal (Sections 2.2.1 and 2.2.2).

2. Connect the loopback connector to the 25-pin RS-232 port
(Figure 2-2).
3. Type one of the following sequences:
ESC [ 4 ; 2 y
Runs the test once.
ESC [ 4 ; 2 ; 9 y
Runs the test continuously.
NOTE

The continuously running test ends only if an error occurs or you
turn off the terminal. The keyboard does not make a bell tone
during this test.
If the test is successful:
1. The keyboard makes a bell tone.

2. The keyboard's LED indicators tum off.
3. A VT 4 2 o OK message appears on the screen.
If the test finds an error:

The screen displays the following message. See Table 2-3.
VT420 RS-232 Port Error -- 2

Troubleshooting and Testing

2.2.6 RS-232 Port Control Lines Loopback Test
(25-Pin, Worldwide Model Only)
This test checks the following control signals:
Data terminal ready (DTR)
Request to send CRTS)
Carrier detect (CD)
Data set ready (DSR)
Clear to send (CTS)
To run the test:

Use an RS-232 loopback connector, PN 12-15336-00.
1. Set up the terminal (Sections 2.2.1 and 2.2.2).

2. Connect the loopback connector to the 25-pin RS-232 port
(Figure 2-2).
3. Type one of the following sequences:
ESC [ 4 ; 6 y
ESC [ 4 ; 6 ; 9 y

Runs the test once.
Runs the test continuously.

NOTE

2. The keyboard's LED indicators turn off.
3. A VT420 OK message appears on the screen.
If the test finds an error:

The screen displays the following message. See Table 2-3.
VT420 RS-232 Port Controls Error -- 3

18 Troubleshooting and Testing

2.2.7 Printer Port Loopback Test (6-Pin}
For this test, you connect the printer transmit and receive data lines
together with a loopback connector (Figure 2-2). The terminal sends a
predefined set of characters on its transmit line and receives them on
its receive line. Then the terminal compares the output characters to the
input characters. If the characters do no match, an error message appears
on the screen.
To run the test:

Use a DEC-423 loopback connector, PN 12-25083-01.
1. Set up the terminal (Sections 2.2.1 and 2.2.2).
2. Connect the loopback connector to the 6-pin DEC-423 port.
3. Type the following sequences:
ESC [ 4 ; 3 y
Runs the test once.
ESC [ 4 ; 3 ; 9 y
Runs the test continuously.
NOTE

The continuously running test ends only if an error occurs or you
turn off the terminal. The keyboard does not make a bell tone
during this test.
If the test is successful:

1. The keyboard makes a bell tone.
2. The keyboard's LED indicators are off.
3. A VT420 OK message appears on the screen.
If the test finds an error:

The screen displays the following message. See Table 2-3.
VT420 DEC-423 Port Error -- 6

2.2.8 Screen Alignment Test
This test fills the screen with uppercase E's. Use this display to adjust
the display height, width, and linearity. See Chapter 4 for the adjustment
procedures.

Troubleshooting and Testing

To run the test:
1.

Set up the terminal (Sections 2.2.1 and 2.2.2).

2. Check the following settings in the Display Set-Up screen:
•

Make sure the columns feature is set to so Columns.

•

Set the number of lines/screen feature to 24 Lines/Screen.

3. Type ESC # 8. The screen fills with a pattern of uppercase E's.
4. Perform the adjustment procedures in Chapter 4.

2.3 Printer Problems
If the VT420 is connected to a local printer, you may have to troubleshoot
some printer problems. The following procedure helps you isolate the
problem to the printer or the terminal.

To troubleshoot printer problems:
1.

Run the power-up self-test (Section 2.2.3).
If the terminal passes the test, go to step 2.

2. Run the printer port loopback self-test (Section 2.2. 7).
If the terminal passes this test, go to step 3.
NOTE
If your terminal passes the above tests, it is running correctly.

The problem is probably not in the terminal.
3. Test the printer. See your printer's service guide for the correct
procedures. If your printer is operating correctly, go to step 4.
4. Go to the Printer Set-Up screen.
•

Check the following settings. They must match the printer's
settings. See your printer's service guide for the correct settings.
Baud rate
Data bits/character
Parity

•

Make sure Printer: Ready appears on the VT420 status line.

5. Make sure you are using the correct cable between the terminal and
printer (Appendix A). Make sure the connections are secure at both
ends of the cable.

20 Troubleshooting and Testing

6. Set up the terminal (Sections 2.2.1 and 2.2.2).
7. Type the following sequence: ESC # 8.
The screen displays a test pattern of uppercase E's.
8. Press the ~ (Print) key. If the printer is operating correctly, the test
pattern displayed on the screen should print out.

2.4 Error Codes
If the self-test finds an error, the terminal

•

Stops operating

•

Makes the keyboard bell tone sound

•

Displays an error message in the upper-left comer of the screen

Table 2-3 lists the error messages and solutions.
Table 2-3 VT420 Display Error Codes
Error Message

Solution•

VT420 NVR Error - 1

2.
3.
4.
5.

Press~ ( IA1tl SetUpl) to enter
the Set-Up Directory.
Move the cursor to the Default
field and press !Enter~
Move the cursor to the Save field
and press IEnter~
Move the cursor to the Global field
and press !Enter~
Move the cursor to the second
field on the second line. Press
IEnter! until the setting changes to
Sl-Comml,S2•Comm2.

6.
7.
8.
9.
10.
*Section numbers follow the solution.

Press ~ ( IA1t 11 SetOp I ) to leave
set-up.
Press ~ to switch sessions.
Repeat steps 1 to 3 for the second
session.
Press~ ( IA1tl ls.top to leave
set-up.
Turn the VT420 off, then on.

Troubleshooting and Testing

Table 2-3 (Cont.)

VT420 Display Error Codes

Error Message

Solution*
If the error continues, replace the
terminal board (3.3).
Replace the terminal board (3.3).

11.
RS-232 Port Data Error - 2

(worldwide model only)
RS-232 Port Controls Error - 3

Replace the terminal board (3.3).

(worldwide model only)
Keyboard Error - 4

DEC-423 Port Error - 5
Printer Port Error - 6
*Section numbers follow the solution.

Make sure the keyboard is plugged
in.
2.
Replace the keyboard (3.4).
3.
If the error continues, replace the
terminal board (3.3).
Replace the terminal board (3.3).
Replace the terminal board (3.3).

This chapter shows you how to remove and replace the field replaceable
units (FRUs) for the VT420. See Appendix B for the recommended spares
list.
CAUTION

Always use a static protection kit (PN 29-26246-00) when handling
static-sensitive material.
This chapter covers all three models of the VT420, the North American
model and the two worldwide models. Where differences occur, the
worldwide procedure appears first, then the North American procedure.

3.1 Top Cover
Remove the top cover as follows. You can leave the tilt-swivel base in
place.
1. Turn off the terminal and unplug the power cord from the wall outlet.

If you have a worldwide model, you can disconnect the power cord
from the back of the terminal, as well.

Removing and Replacing FRUs 23

2. Place the terminal facedown on a clean piece of paper, to avoid
scratching the bezel.

GSF _1'38_89.DG

24 Removing and Replacing FRUs

3. Loosen the two captive screws at the base of the bezel so the screws
extend out from the top cover.

GSF _ 1439_89.DG

4. Grasp the rear of the top cover firmly with one hand. Place your other
hand securely on the base assembly.
5. With your hands in position, push down on the base assembly and
pull the top cover away from the base. Place the cover aside.

Removing and Replacing FRUs 25

GSF _ 1440_89.0G

To install the top cover:

Extend the captive screws out from the top cover.

2. Slide the top cover into the front bezel so the two tabs on the top of
the bezel align with the cover. Align the rest of the cover with the
base assembly.
3. Align and tighten the captive screws.
On the North American model, make sure the small connector cover is
installed on the rear panel.

Removing and Replacing FRUs

3.2 CRT/Yoke/Bezel Assembly
To remove the CRT/yoke/bezel assembly:
1.

Turn off the terminal and unplug the power cord from the wall outlet.

2. Remove the top cover (Section 3.1).
WARNING

The following steps may expose you to high voltages. To
protect yourself, discharge the anode with anode discharge
tool (PN 29-24717-00).
3. Discharge the anode as follows.
a. Attach the alligator clip of the anode discharge tool to the
grounding braid on the rear of the CRT.
WARNING

The support bracket assembly is not a ground point.
b. Insert the tool under the rubber anode cap until you make contact
with the anode connector. Discharge the anode for at least three
seconds.

Not a
Ground Point

GSF_1441_89.DG

Removing and Replacing FRUs 27

Remove the anode discharge tool.

4. Remove the CRT anode connector from the CRT.
a. Grasp the rubber anode cap and push the cap away from you.
b. Press the front of the cap with you thumb and lift the front up to
get one of the wire prongs out of the anode hole. Lift the cap to
ensure the wire prong is out of the hole.
c.

If both of the wire prongs are still in the anode hole, repeat the
previous steps until one is out.

d. Pull the back of the rubber anode cap forward and lift up to get
the other wire prong (the anode connector) out of the anode hole.

GSF _ 1'42_19.DG

Removing and Replacing FRUs

NOTE

If you have a North American model, skip the next two steps.

5. If you have a worldwide model, disconnect the ground clip from the
hood.

GSF _ 1443_811.0G

Removing and Replacing FRUs 29

6. If you have a worldwide model, loosen the two screws securing the
hood and remove the hood.

GSF_1444_89.DG

30 Removing and Replacing FRUs

7. Disconnect the ground clip from the arc protection board.

GSF _ 1US_ll.DG

Removing and Replacing FRUs 31

8. Remove the arc protection board from the back of the CRT.

GSF_1447_89.0G

CAUTION

To prevent damage to terminal board components, be careful
when you unlock and remove the yoke wiring harness
connector in the next step.

To prevent damage to the connector wires, only pull on the
connector.

Removing and Replacing FRUs

9. Disconnect the locking connector on the yoke wiring harness from the
terminal board by pushing the locking tab and pulling the connector.

GSF_ 1'0_19.DG

10. Separate the base from the CRT/yoke/bezel assembly, as follows:
a. Release the two base support brackets.

Removing and Replacing FRUs 33

b. Lift or pull the base away from the CRT/yoke/bezel assembly.

GSF _ 1450_89.DG

To install the CRT/yoke/bezel assembly, reverse the installation steps.

Removing and Replacing FRUs

3.3 Terminal Board Assembly
To remove the terminal board assembly:
CAUTION

To prevent damage to internal components, do not replace the
fuse if it burns out. A burnt fuse is a symptom of a problem inside
the terminal.
1. 'furn off the terminal and unplug the power cord from the wall outlet.

If you have a worldwide model, you should also disconnect the power

cord from the back of the terminal.
2. Disconnect all cables from the terminal.
3. Remove the top cover (Section 3.1).
4. Remove the CRT/yoke/bezel assembly (Section 3.2).
5. Loosen the captive screw in the center of the terminal board.

GSF _ 1,52_1t.OG

Removing and Replacing FRUs 35

6. Pull the board away from the plastic tab on the connector side of the
terminal board. You can release the tab by inserting a screwdriver
through the hole below the tab.
7. Lift the terminal board out of the base.

GSF _ 1453_H.OG

To install the terminal board assembly, reverse the installation steps. If
you need to adjust the video display, refer to Chapter 4.

Removing and Replacing FRUs

3.4 Keyboard
If the keyboard is faulty, replace the keyboard. Turn the terminal off and

disconnect the keyboard cable from the keyboard cable connector on the
right side of the terminal. Remove and save the legend strip. The PC
(LK443/LK444) keyboard does not have a legend strip.
To install a new keyboard:
1. 'furn the terminal off.

2. The keyboard cable is already connected to the back of the keyboard.
If you want the keyboard cable routed to the right or left, press it into
one of the grooves on the bottom of the keyboard.
3. Insert the other end of the cable into the keyboard connector on the
right side of the terminal.
4. 'furn the terminal on.

GSF _0&14_H.DG

Removing and Replacing FRUs 37

5. If you want the keyboard raised up, lower the two legs on the bottom.
6. Turn the keyboard over. Install the legend strip, aligning the strip
with the tabs.
ANSI (LK401) keyboard: Place the strip below the top-row function
keys as shown.
Short ANSI (LK421) keyboard: Place the strip above the top-row
function keys.

GSF .0127_11.DG

38 Removing and Replacing FRUs

3.5 CRT Disposal (Digital Service Representatives
Only)
This section describes how to safely dispose of the monitor's cathode-ray
tube (CRT).
NOTE

This procedure replaces any other tech tips on replacing and
disposing of CRTs. This procedure is for Digital personnel
only, and is not intended for use by OEM and self-maintenance
customers.
CRTs are glass vacuum tubes. Because air pressure outside the tube
is greater than air pressure inside, there is always the possibility of
accidental implosion.
WARNING

You must handle CRTs very carefully to avoid accidental
implosion and shattering glass.
To prevent personal injury from CRT implosion, use the following
guidelines and disposal procedure to remove and dispose of a CRT. These
guidelines and procedure are Digital service policy for all CRTs more than
three inches in diameter.
Location

Work in areas where risks and exposure are limited to trained Digital
service personnel. Only Digital service personnel should be in the area
during CRT removal and replacement.
Protective Gear

Any service person replacing a CRT must wear at least safety goggles and
the approved gloves.
Safety goggles
PN 29-16141
Gloves
PN 29-16146
WARNING

To avoid injury to the eyes or hands, always wear goggles and
gloves when you work with a CRT.

Removing and Replacing FRUs 39

Handling a CRT

•

Never handle the CRT by the neck. Always use two hands and hold
the CRT by the sides near its face.

•

Keep the CRT away from your body during handling.

•

Do not let the neck strike anything.

•

Do not rest the CRT on its neck.

•

Do not let the CRT touch any tools, such as screwdrivers and soldering
irons.

Stocking and Storage

All CRTs must be kept in a closed container or mounted on the device
cabinetry.

CRT Disposal
Use the following procedure to safely dispose of CRTs. Always perform
this procedure at a Digital facility.
WARNING
Do not dispose of any CRT until it is rendered inoperative and
safe to dispose.

Never perform the following disposal procedure at the customer
site. Return the defective CRT to the local Digital facility for
disposal.
At the Digital facility you will need
•

An area clear of nonessential personnel

•

A second person in the area in case of an emergency

•

Safety goggles (PN 29-16141)

•

Gloves (PN 29-16146)

•

Pliers (PN 19-10008)

WARNING
Be careful when performing this procedure. For your safety, you

must use the specified gloves and goggles.

40 Removing and Replacing FRUs

Never handle pieces of phosphor coated glass without wearing
protective gloves.
1.

Place the old CRT and the original packing material in the container
from which you removed the new CRT.

GSF_14S1_89.DG

Removing and Replacing FRUs 41

2. Seal up the container so that only the very tip of the CRT neck is
exposed.
3. Using the specified pliers, slowly crush, but do not snap, the
evacuation point. Do not move or disturb the CRT until the hissing
sound of inrushing air has stopped.
NOTE

The evacuation point is a protrusion that extends from
the circular area defined by the CRT neck pins. The glass
protrusion is sometimes encased in a protective plastic cap,
and more force is required to crush it.
4. Seal the carton with packing tape and dispose of it in the Digital site's
trash compactor or receptacle.
NOTE

This safe gassing of the CRT is necessary to prevent liability and
safety problems that may arise from accidental CRT implosion.

This chapter describes how to adjust the VT420 monitor. You do not have
to perform every adjustment each time you align the monitor. However,
you should check all adjustments in the order shown, because many
adjustments affect each other. If a setting is already correct, you can skip
that adjustment and go on to the next setting.

4.1

Aligning the Screen

The alignment of the screen on the VT420 may have changed after
shipping. This change occurs when the VT420 is shipped to countries
where the magnetic field of the earth is different from that of the shipping
location. Before making any adjustments inside the monitor, align the
screen from the Set-Up Directory screen.
Center or rotate the border of the screen as follows:
Use the arrow keys to move the cursor in all set-up screens.
The IEnter I and IReturn I keys perform the same function in all set-up screens.
1. Press the~ (Set-Up) key to enter set-up. The Set-Up Directory

screen appears (Figure 4-1). The cursor is on the Global Set-Up
field.

Adjusting The Video Monitor 43

Worldwide
Set-Up Directory
Ml@I

Display

Clear Display

VT420 V1 .O

General

Clear Comm

Comm

Printer

Keyboard

Reset Session

Recall

Set-Up .. English

North American Keyboard

Enable Sessions

Disable Sessions

Exit

Tab

Save

Default

Screen Align

North American
Set-Up Directory
MIMI Display
Clear Display
Default

General

Clear Comm

VT420 AV1 .0
Comm

Printer

Reset Session

Keyboard
Recall

Tab

Save

Screen Align

Enable Sessions

Disable Sessions

Exit

002 003)

Pr r1 1

,J'J -1

'v1'.Jci 1 n1

[ -- ::~

Session 1

GSF _ 15811_89.DG

Figure 4-1

Set-Up Directory Screens

2. Move the cursor to the Screen Align field.
3. Press IEnterl and follow the instructions that appear on the screen
(Figure 4-2).

44 Adjusting The Video Monitor

Worldwide

North American

GSF _ 1590_90.0G

Figure 4-2

Screen Align Screens

NOTE
The North American model of the VT420 does not have the

feature to rotate the active display on the screen.

Adjusting The Video Monitor 45

4. When you have finished centering or rotating the border, return to the
Set-Up Directory. Move the cursor to the Save field.
5. Press IEnter~ This saves all the current settings in each set-up screen.
A Done message appears at the bottom of the screen.
6. Press ~ to leave set-up.

4.2 Monitor Adjustments
Figure 4-3 shows the location of the controls you use to make
adjustments.

Vertical Size
(V-SIZE)
(R619) (Clear)

Horizontal Hold
(H-HOLD)
(R615) (Black)

Width Coil
(L602) (White)

Screen
Static Focus (RSS?) (Blue)
(R656) (Blue)

GSF _ uu_a9.DG

Figure 4-3

Monitor Adjustment Controls

46 Adjusting The Video Monitor

4.2.1 Before You Start
Before you perform any adjustments, complete the following steps:
WARNING

The following procedures expose you to high voltages. Use
caution when performing them.
1. Remove the top cover (Section 3.1).

2. Plug in the power cord.
3. 'furn the power switch on by moving it toward the ( I ). Wait for the
VT420 OK message to appear on the screen.
4. Make sure all shields are in place before doing any adjustments.

4.2.2 Displaying the Screen Test Pattern
You use the same screen test pattern for all monitor adjustments. The
test pattern is a screen full of E's (Figure 4-4). To display the test pattern:
1. Set up the terminal (Sections 2.2.1 and 2.2.2).

2. Enter the sequence ESC # 8 to display a screen full of E's.
If you do not know how to enter an ESC character, see Section 2.2.2.
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
MA·XIUl·ll

Figure 4-4

Screen Test Pattern

Adjusting The Video Monitor 47

4.2.3 Screen Control
To adjust the screen control:
1. On the front of terminal, set the brightness control to maximum and
the contrast control to minimum.
2. Adjust the screen control (R657) until the white background (raster)
almost disappears, but is still visible.
3. Readjust the brightness control to the user's preference.

4.2.4 Subcontrast
To adjust the subcontrast control:
1.

Display the alignment pattern of E's (Section 4.2.2).

2. Set the contrast control on the front of the terminal to maximum.
3. Turn the brightness control on the right side of the terminal until the
raster just disappears.
4. Adjust the SUB CONTRAST control (R647) to the maximum intensity,
maintaining the focus of screen characters.
5. Readjust the contrast control to the user's preference.

4.2.5 Rotation
Worldwide Model

To adjust the rotation:
1.

Recall the default settings for the terminal by using the Default field
in the Set-Up Directory.

2. Adjust the rotation by using the Screen Align field in the Set-Up
Directory.
North American Model

To adjust the rotation:
1.

Display the alignment pattern of E's (Section 4.2.2).
WARNING

The next step exposes you to the CRT anode, which stores a
high voltage. Use caution when working this area.
2. Loosen the yoke clamp screw on the CRT neck (Figure 4-5).

Adjusting The Video Monitor

3. Gently rotate the yoke until the display is square and level on the
CRT/yoke/bezel assembly.
CAUTION

Make sure you take up the slack on the CRT clamp before you
tighten the screw. Do not overtighten, or you may crack the
CRT neck.
4. Tighten the screw on the CRT connector clamp.

GSF_l46'_19.0G

Figure 4-5

Rotation and Centering Adjustment

Adjusting The Video Monitor 49

4.2.6 Horizontal Width
Check and adjust the horizontal width as follows. You need a metric
measuring tape (PN 29-25342).
1.

Display the Screen Align screen by selecting the Screen Align field in
the Set-Up Directory screen.

2. Use your metric measuring tape to measure the width of the active
video display.
3. If the size does not measure approximately 232 mm, use the tuning
wand (PN 29-26128-00) to adjust the horizontal WIDTH (L602) coil.

4.2.7 Vertical Height
To check and adjust the vertical height:

1. Display the Screen Align screen by selecting the Screen Align field in
the Set-Up Directory screen.
2. Use your metric measuring tape to measure the height of the active
video display. If the size does not measure approximately 168 mm,
use the tuning wand to adjust the V-SIZE control (R619).
3. If necessary, readjust the vertical linearity {V-LIN) (R611)
(Section 4.2.8).

4.2.8 Vertical Linearity
To check and adjust the vertical linearity:
1.

Display the alignment pattern of E's (Section 4.2.2).

2. Check the height of the E characters on the top and bottom rows of
the display. All characters should appear to be the same size.
3. If necessary, use the tuning wand to adjust the V-LIN control (R611)
until all characters are the same height.
4. If necessary, readjust the vertical height CV-SIZE) (R619)
(Section 4.2. 7).

Adjusting The Video Monitor

4.2.9 Centering
To check and adjust the centering of the screen display:
1.

Display the Screen Align screen by selecting the screen Align field in
the Set-Up Directory screen (Figure 4-2).

2. Follow the instructions on the screen to center the active video display.
3. If you are not able to center the display, select the Default field from
the Set-Up Directory screen to recall the factory-default settings.
4. Make sure you have completed the following adjustments, if they are
needed:
Screen control
Subcontrast
Rotation
Horizontal width
Vertical height
Vertical linearity
5. Use the centering rings on the neck of the CRT to center the active
video display within the CRT bezel (Figure 4-5).

4.2.1 O Focus
To check and adjust the focus:
1. Display the alignment pattern of E's (Section 4.2.2).
2. Check the E characters at the four corners and at the center of the
screen. The characters should appear clearly in focus.
NOTE

Make sure the screen is clean. This condition can appear to
affect the focus.
3. If necessary, adjust the STATIC FOCUS control (R656) so that you
can see each character clearly and distinctly.

The VT420 terminal has a series of set-up screens that let you change the
settings of operating features from the keyboard. This chapter provides a
brief summary of how to use set-up. The set-up chapter in Installing and
Using the VT420 Video Terminal describes the set-up screens in detail.
Each set-up screen provides a group of related features, such as
communication or display features. You can move from one set-up screen
to the other to change or review settings.

5.1

Displaying Set-Up Screens

To enter or leave set-up, you press ~~Al.ti l~)P~ When you enter

set-up, the Set-Up Directory appears ( gure

You can select any set-up screen from the Set-Up Directory. Use the
arrow keys to move the cursor to name of the desired screen. Then press
the IEnterl or IReturn I key to display that screen.

Using Set-Up

Worldwide
Set-Up Directory
HMiiii

Display

Clear Display

VT420 V1 .0

General

Clear Comm

Comm

Printer

Keyboard

Reset Session

Recall

Set-Up=English

North American Keyboard

Enable Sessions

Disable Sessions

Exit

Tab

Save

Default

Screen Align

Prrnter

Ready

Modem

DSR

Session 1

North American
Set-Up Directory
GMiiil

Display

Clear Display
Default

General

Clear Comm

VT420 AV1.0
Comm

Printer

Reset Session

Keyboard
Recall

Tab

Save

Screen Align

Enable Sessions

Disable Sessions

Exit

Prrnter

Ready

Modem

DSR

Session 1

GSF _ 1589_89.DG

Figure 5-1

Set-Up Directory Screens

Using Set-Up 53

5.2 Changing Settings
You use the arrow keys to move to different fields in each set-up screen.
The cursor highlights the selected field in reverse video.
Some set-up features are action fields. Others are parameter fields with
two or more possible settings.
Action fields
Move the cursor to the desired field. Then press lEnterl or
IReturn I to have the t.erminal perform the action.
Move the cursor to the desired field. Then press IEnter Ior IReturn I
Paramet.er
to st.ep through the values until the desired value appears.
fields

5.3 Saving Set-Up Values
You should save the current settings in set-up before you run tests.
Inform the user about your action. Saving the user's current settings
before you run tests enables you to recall them later.
To save the current set-up settings:
1.

Press ~ ( !Alt 11 SetOp I to enter Set-Up. The Set-Up Directory appears.

2. Use the arrow keys to move the cursor to the Save field.
3. Press !Enter~ This procedure saves the current settings in all set-up
screens.
The save feature stores the current values of the set-up features. The
terminal uses these values until you change them.

5.4 Recalling Set-Up Values
You can reset the terminal to the previous set-up values by recalling the
values from the Set-Up Directory screen. You can select two types of
set-up values. Ask the user which settings were in use.
•

Recall (user's saved settings)

•

Default (factory-default settings)

To select
1. Saved settings-Move the cursor to the Recall field and press !Enter~
2. Factory-default settings-Move the cursor to the Default field and
press IEnteri

You can order the following modems, cables, and manuals from Digital for
the North American and worldwide versions of the VT420. See the end of
this appendix for ordering information.

A.1

Modems

Part Number

Description

DF242 Scholar Plus

300, 1200, and 2400 baud, full-duplex asynchronous

DF224

300, 1200, and 2400 baud, full-duplex, asynchronous

DF124

300, 600, and 1200 baud, full-duplex, asynchronous

A.2 Cables
Figure A-1 shows cable connections to the VT420.
Part Number

Length

Connector

Printer Cables and Adapter (VT420 to printer)
BC16E-10

3 m (10 ft)

6-pin M DEC-423 to

BC16E-25

7.6 m (25 ft)

6-pin M DEC-423

H8751-A adapter

6-pin F DEC-423 to
25-pin F RS-232

H8751-C or -F adapter

25-pin F RS-232 to
6-pin M DEC-423

M = male. F = female.
xx = length in feet (10, 25, 50, 100, 200, 250).

Modems, Cables, and Documentation

Length

Connector

BC22E-10

3 m (10 ft)

25-pin F RS-232 to

BC22E-25

7.6 m (25 ft)

25-pin M RS-232

Part Number

Extension Cables

Null Modem Cables

25-pin F RS-232 to
25-pin F RS-232

BC22D-xx
Communication Cables
3 m (10 ft)

6-pin M DEC-423 to

BC16E-25

7.6 m (25 ft)

6-pin M DEC-423

AC Power Cables

Country

BN20V-2E

Australia, New Zealand

BN20S-2E

Austria, Belgium, Finland, France, Germany,
Netherlands, Norway, Portugal, Spain, Sweden

BN20P-2E

Canada

BN20U-2E

Denmark

BN20R-2E

Ireland, United Kingdom

BN19U-2E

Israel

BN20W-2E

Italy

BN20T-2E

Switzerland

BC16E-10

M = male. F = female.
xx = length in feet (10, 25, 50, 100, 200, 250).

Modems, Cables, and Documentation

6-Pin Comm2
(Printer) Port
H8571-A
Adapter

!llll1;:r.;i...----

8C16E Cable

-------------------------------------~~~P-ri_n_te_r_

6-Pin
Comm Port

H8571-C or -F
Adapter

%1d___
~

:8'.l

,..6 d

e_c_1_s_e__c_a_b_1e____________________

6-Pin
Comm Port

Modem

H8571-C or -F
Adapter
BC16E Cable

BC22E Cable

+-------------..M F Host
L

6-Pin
Comm Port
BC16E Cable

H8571-C or -F
Adapter
Null
Modem Cable

+-----------~F

BC22D-xx

M Host
L

RS-232 25-Pin
Comm1 Port
H8571-A

~-t-e_r

________s_c
__
16_e_c_a_b_1_e__________

_,..~

Host

GSF _ 1465_89.0G

Figure A-1

VT420 C8bles

Modems, Cables, and Documentation

A.3 Related Documentation
You can order the following VT420 documents from Digital:
Installing and Using the VT420 Video Terminal
Provides users with the information needed to install, operate, and maintain the
VT420 terminal. Also provides a summary of programming control functions.
There are two versions of this manual.

North American Model

EK-VT420-UG

Worldwide Model

EK-VT420-UU

Installing and Using the VT420 Video Terminal with
PC Terminal Mode

EK-VT42A-UU

Provides users with the information needed to install, operate, and maintain
the VT420 terminal with PC terminal mode. Also provides a summary of
programming control functions.

VT420 Programmer Reference Manual

EK-VT420-RM

Provides information on character processing, character codes, and control
functions available for all VT420 applications including PC terminal mode.

VT420 Video Terminal IDustrated Parts Breakdown

EK-VT420-IP

Provides a detailed parts breakdown of the terminal's field replaceable units. Does
not provide part numbers for printed circuit board components.

VT420 Family Field Maintenance Print Set

MP-o2949-0l

Provides a complete set of VT420 electrical and mechanical schematic diagrams.

Installing and Using the Session Support Utility

AA..JB84C-TE

Provides system managers with instructions for installing SSU software to support
two sessions over one communication line. The guide is part of an SSU software
kit. The kit is available on different media.

This appendix has two sections.
•

Section B. l lists the available models of the VT420 video terminal.

•

Section B.2 lists the spare components that a Digital service
representative should have when servicing a VT420 video terminal.

•

Section B.3 lists the keyboard model numbers.

8.1

VT420 Models

The VT420 comes in the following basic models and versions:

Location

Model
Number

Screen
Color

Power
Requirement

North American Terminals (Standard Version)
North America

VT420-A2
VT420-B2
VT420-C2

White
Green
Amber

120V
120V
120V

Worldwide Turminals (Standard Version)
Northern Hemisphere

VT420-A4
VT420-B4
VT420-C4

White
Green
Amber

100 v t.o 240 v
100 v t.o 240 v
100 v t.o 240 v

VT420 Recommended Spares 59

Model
Number

Screen
Color

Power
Requirement

Southern Hemisphere

VT420-A5
VT420-B5
VT420-C5

White
Green
Amber

100 v to 240 v
100 v to 240 v
100 v to 240 v

Israel (Hebrew)

VT420-A7
VT420-B7
VT420-C7

White
Green
Amber

100 v to 240 v
100 v to 240 v
100 v to 240 v

Greece

VT420-A8
VT420-B8

White
Green

100 v to 240 v
100 v to 240 v

Turkey

VT420-A9
VT420-B9
VT420-C9

White
Green
Amber

100 v to 240 v
100 v to 240 v
100 v to 240 v

Automatic Data
Processing, Inc. (ADP)

VT42C-B4

Green

100 v to 240 v

Olivetti

WS885-A4
PC TERM
WS885-B4
PC TERM
WS885-C4
PC TERM

White

100 v to 240 v

Green

100 v to 240 v

Amber

100 v to 240 v

Location

Worldwide 'Thrminal (Low-Emission Version)
VT420-A6

White

100 v to 240 v

VT420-D6
PC TERM

White

100 v to 240 v

Kodak

VT42C-Al

White

100 v to 250 v

Olivetti

WS885-L
PC TERM

White

100 v to 240 v

Northern and Southern
Hemispheres

VT420 Recommended Spares

B.2 Recommended Spares
The following is a list of recommended spares for the VT420 video
terminal:

Assembly

Part
Number

Tilt-swivel base

70-26541-01

Top cover

70-26542-01

Bottom cover

70-26535-01

Model Number

CRT/bezel/yoke
White

70-26534-04

Green

70-26534-05

Amber

70-26534-06

White (low emission)

70-26534-07

ADP 70-26534-15

VT42C-B4

Terminal board
North American

70-26536-01

VT420-A2, -B2, -C2

Worldwide: Northern and
Southern Hemispheres

70-26536-02

VT420-A4, -B4, -C4, -A5,
-B5, -C5

Worldwide: Hebrew

70-26536-04

VT420-A7, -B7, -C7

Worldwide: Olivetti

70-26536-05

WS885-A4, -B4, -C4 (PC
TERM)

Worldwide: Greek

70-26536-07

VT420-A8, -BS

Worldwide: Turkish

70-26536-08

VT420-A9, -B9, -C9

Worldwide: ADP

70-26536-12

VT42C-B4

Low emission: Northern
and Southern Hemispheres

70-26536-03

VT420-A6

70-26536-11

VT420-D6 (PC TERM)

70-26536-06

WS885-L (PC TERM)

Low emission: Olivetti

VT420 Recommended Spares 61

Loopback Connector

Part Number

DEC-423 port

12-25083-01

RS-232 port

12-15336-00

B.3 Keyboard Models
The keyboards for the VT420 are available in the following versions:
Model Number
Standard.

WPS

North America/United Kingdom

LK401-AA

LK402-AA

Belgium (Flemish)

LK401-AB

LK402-AB

Country
LK401 ANSI Keyboard

Canada (English)

LK401-AE

Canada (French)

LK401-AC

LK402-AC

Denmark

LK401-AD

LK402-AD

Finland

LK401-AF

LK402-AF

France/Belgium

LK401-AP

LK402-AP

Germany/Austria

LK401-AG

LK402-AG

Italy

LK401-AI

LK402-AI

Netherlands (Dutch)

LK401-AH

LK402-AH

Norway

LK401-AN

LK402-AN

Portugal

LK401-AV

LK402-AV

Spain

LK401-AS

LK402-AS

Sweden

LK401-AM

LK402-AM

Switzerland (French)

LK401-AK

LK402-AK

Switzerland (German)

LK401-AL

LK402-AL

LK421 Short ANSI (UNIX) Keyboard

North America/United Kingdom

LK421-AA

VT420 Recommended Spares

Model Number
Country

Standard

LK443 PC Keyboard

Canada (French)

LK443-AC

North America

LK443-AA

LK444 (PC) Keyboard

Australia/New Zealand

LK444-AZ

Belgium

LK444-AB

Canada (English)

LK444-AQ

Denmark

LK444-AD

Finland

LK444-CA

France

LK444-AP

France (English)

LK444-AQ

Germany/Austria

LK444-AG

Italy

LK444-AI

Netherlands (Dutch)

LK444-AH

Norway

LK444-AN

Portugal

LK444-AV

Spain

LK444-AS

Sweden

LK444-AM

Switzerland (French/German)

LK444-CH

United Kingdom/Ireland

LK444-AE

WPS

This appendix shows the components and pin assignments for the North
American and worldwide models of the VT420 video terminal.
Figure C-1 shows the components of the North American model.
Figure C-2 shows the components of the worldwide models.

Physical/Functional Diagrams

P701
-.....,.,.._...__ GRNG1
BLEG4
J701
'-+~~++;z-- BANH 1
REDG2

R647 SUB
CONTRAST
R619 V-SIZE-.+.-G
R611 V-LIN
R615 H-HOLD

P6-RED
P7-BLUE

Comm2/
Printer
DEC-423

Comm1
DEC-423

AC IN

GSF _ 1466_811.DG

Figure C-1

VT420 North American Model

VT420 North American Model: Signals and Pin Assignments
Tennlnal Board Assembly
Jl DEC-423 Com.ml Port Connector
Pin
1
HDTR2
Data terminal ready
Transmitted data
2
HTXD2
Transmit ground
3
GND
Receive ground
HCOM
4
Received data
5
RXD2

Physical/Functional Diagrams 65

6
DSR2
Data set ready
J2 DEC-423 Com.m21Printer Port Connector
Pin
1
HPI'RDTR
Data terminal ready
2
HPI'RTXD
Transmitted data
3
GND
Transmit ground
4
PI'RCOM
Receive ground
5
PI'RRXD
Received data
PI'RDSR
Data set ready
6
J3 Keyboard Port Connector
1
HKBTXD
Transmitted data
Ground
2
GND
3
+12V
KBRXD
Received data
4

CRT/Yoke/Bezel Assembly
J601 CRT Yoke Connector
Pin
1
No connection
2
No connection
3
Vertical yoke
4
Vertical yoke
5
Horizontal yoke
6
Horizontal yoke

Arc Protection Board Assembly
J701 CRT Socket Connector
GRNGl
Pin
1
YELK2
2
BRNHl
3
P701 (H2)
4
Not used
5
REDG2
6
BLUG4
7

Grid 1 (green)
Cathode (yellow)
Heater -12 V (brown)
Heater ground (black)
Grid 2 (red)
Grid 4 (blue)

Physical/Functional Diagrams

P701

-.._or--_ _ GR NG 1
BLEG4
J701
L-+-~-.i...+;r-- BR NH 1
REDG2

R647 SUB
CONTRAST

0304

R619 V-SIZE--1-*o
P1-GREEN

R611 V-LIN

PS-RED
Comm2/ Comm1
Printer
DEC-423
DEC-423

Comm1
RS-232
LJ·01628· TIO

Figure C-2

VT420 Worldwide Models

VT420 Worldwide Model: Signals and Pin Assignments
Terminal Board Assembly
Jl DEC-423 Com.ml Port Connector
Pin
1
HDTR2
Data terminal ready
2
HTXD2
Transmitted data
3
GND
Transmit ground
Receive ground
HCOM
4
Received data
RXD2
5

Physical/Functional Diagrams 67

6
DSR2
Data set ready
J2 DEC-423 Comm2/Printer Port Connector
Pin
1
HPl'RDTR
Data terminal ready
2
HPl'RTXD
Transmitted data
3
GND
Transmit ground
Pl'RCOM
4
Receive ground
5
Pl'RRXD
Received data
PrRDSR
Data set ready
6
J3 RS-232 Comml Port Connector
Pin
1
GND
Ground
HTXDl
2
Transmitted data
3
RXDl
Received data
HRTS
4
Request to send
5
CTS
Clear to send
6
DSRl
Data set ready
7
SIGGND
Signal ground
8
HCD
Carrier detect
Not used
9
10
Not used
Not used
11
12
SPDIND
Speed indicator
13
Not used
14
Not used
Not used
15
16
Not used
17
Not used
Not used
18
19
Not used
20
HDTRl
Data terminal ready
21
Not used
Not used
22
HSPDSEL
Speed select
23
Not used
24
Not used
25
J4 Keyboard Port Connector
1
HKBTXD
Transmitted data
2
GND
Ground
3
+12V
Received data
4
KBRXD

Physical/Functional Diagrams

CRT/Yoke/Bezel Assembly
J601 CRT Yoke Connector
Pin
1
Rotation coil (green)
2
Rotation coil (black)
3
Vertical yoke (brown)
4
Vertical yoke (yellow)
5
Horizontal yoke (white)
6
Horizontal yoke (red)

Arc Protection Board Assembly
J701 CRT Socket Connector
1
Pin
GRNGl
2
YELK2
3
BRNHl
P701 (H2)
4
5
Not used
6
REDG2
7
BLUG4

Grid 1 (green)
Cathode (yellow)
Heater -12 V (brown)
Heater ground (black)
Grid 2 (red)
Grid 4 (blue)

HOW TO ORDER ADDITIONAL DOCUMENTATION
From

Call

Write

Alaska, Hawaii,
or New Hampshire

603-884-6660

Digital Equipment Corporation
P.O. Box CS2008
Nashua NH 03061

Rest of U.S.A.
and Puerto Rico1

800-DIGITAL

1Prepaid orders from Puerto Rico, call Digital's local subsidiary (809-754-7575)

Canada

800-267-6219
(for software
documentation)

Digital Equipment of Canada Ltd.
100 Herzberg Road
Kanata, Ontario, Canada K2K 2A6
Attn: Direct Order Desk

613-592-5111
(for hardware
documentation)

Internal orders
(for software
documentation)

DTN: 241-3023
508-874-3023

Software Supply Business (SSB)
Digital Equipment Corporation
Westminster MA 01473

Internal orders
(for hardware
documentation)

DTN:234-4323
508-351-4323

Publishing & Circulation Services (P&CS)
NR02-2/l5
Digital Equipment Corporation
Northboro MA 01532

Index
A

ADP parts, 59, 60

IF11l(ESC)key, 9, 12
Focus adjustment, 50

B
Bell tone problems
does not tum off, 6
no bell tone, 6

c
Cables, 54 to 56
Centering adjustment, 50
Character sets, 2
Communication problems, 6
reverse question marks, 9
Copy and paste problems, 9
CRT disposal, 38
CRT/yoke/bezel assembly removal,
26

D
DEC-423 port loopback test, 14
Documentation, 57

E
Error characters
Reverse question marks, 9
Error messages, 20 to 21
IEscl key, 9, 11
Escape (ESC) characters, 11

H
Horizontal width acljustment, 49

K
Keyboard LED problems
LEDs stay on, 9
Keyboard models, 61 to 62
Keyboard removal, 36
Kodak parts, 59

L
Local mode, selecting, 11
Loopback connectors, 15
Loopback tests
printer port, 18
RS-232 port control lines, 17
RS-232 port data lines, 16

M
Modems
Modem speed problems, 10
part numbers, 54
Monitor acljustments, 45 to 50
centering, 50
controls, 45
Index 1

Index

Monitor adjustments (Cont.)
focus, 50
horizontal width, 49
rotation, 4 7
screen control, 47
subcontrast, 47
test pattern, 46
vertical height, 49
vertical linearity, 49

Power-up self-test, 4, 13 to 14
Printer port loopback test, 18
Protective gear, 38

Screen alignment, 42 to 45
Screen alignment pattern, 18
Screen control adjustment, 47
Screen display problems
blank screen, 7
distorted or jittery, 7
ghost characters, 8
horizontal or vertical lines, 7
off center or rotated, 7
reverse question marks, 9
wrong characters displayed
local mode, 8
on-line, 8
Screen is blank, 6
Scrolling problems, 7
Self-tests, 10 to 21
DEC-423 port loopback, 14
power-up, 13
screen alignment pattern, 18
selecting local mode, 11
Set-up, using
displaying set-up screens, 51
Set-up cursor missing, 10
Set-up screens, using, 51 to 53
Subcontrast adjustment, 4 7

Recommended spares, 60
Removing FRUs, 22 to 41
CRT disposal, 38
CRT/yoke/bezel assembly, 26
keyboard, 36
terminal board assembly, 34
top cover, 22
Rotation adjustment, 47
RS-232 port control lines loopback
test, 17
RS-232 port data lines loopback test,
16

Terminal board assembly removal,
34
Testing, 10 to 21
'Ibols required, vii
Top cover removal, 22
Troubleshooting, 4 to 10
table of problems and solutions, 6

N
North American model, 1
components, 63
model numbers, 58
pin assignments, 64

0
Olivetti parts, 59, 60
Operating modes, 2

Index

v
Vertical height adjustment, 49
Vertical linearity adjustment, 49
VT420 features
common features, 1
VT420 models
description, 1
differences, 3
features compared, 1 t.o 3

overview, 1
part numbers, 58
VT420 rear connect.or panel, 15

w
Worldwide model
components, 65
model numbers, 58
pin assignments, 66
Worldwide models, 1