Digital Equipment VT420 User manual

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
Vll
1 VT420 Models and Features
1.1 VT420 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 VT420 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Troubleshooting and Testing
2.1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.2.8
2.3
2.4
Troubleshooting .................................. .
VT420 Self-Tests ................................. .
Before You Start ................................ .
How to Type an Escape Character .................. .
Power-Up Self-Test .............................. .
DEC-423 Port Loopback Test (6-Pin) ................ .
RS-232 Port Data Lines Loopback Test
(25-Pin, Worldwide Model Only) ................... .
RS-232 Port Control Lines Loopback Test
(25-Pin, Worldwide Model Only) ................... .
Printer Port Loopback Test (6-Pin) .................. .
Screen Alignment Test ........................... .
Printer Problems ................................. .
Error Codes ..................................... .
4
10
11
11
13
14
16
17
18
18
19
20
iii

iv Contents
3 Removing and Replacing FRUs
3.1 Top Cover........................................ 22
3.2 CRT/Yoke/Bezel Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3 Terminal Board Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.5 CRT Disposal (Digital Service Representatives Only) . . . . . . 38
4 Adjusting The Video Monitor
4.1 Aligning the Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2 Monitor Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2.1 Before You Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.2.2 Displaying the Screen Test Pattern . . . . . . . . . . . . . . . . . . 46
4.2.3 Screen Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8
4.2.9
4.2.10
Subcontrast ................................... .
Rotation ...................................... .
Horizontal Width ............................... .
Vertical Height ................................. .
Vertical Linearity ............................... .
Centering ..................................... .
Focus ........................................ .
5 Using Set-Up
47
47
49
49
49
50
50
5.1 Displaying Set-Up Screens. . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.2 Changing Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.3 Saving Set-Up Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.4 Recalling Set-Up Values............................. 53
A Modems, Cables, and Documentation
A.1 Modems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
A.2 Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
A.3 Related Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Contents v
B VT420 Recommended Spares
B.1 VT420 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
B.2 Recommended Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
B.3 Keyboard Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
C Physical/Functional Diagrams
Index
Figures
2-1 VT420 Video Terminal with Keyboards . . . . . . . . . . . . . . . . . 5
2-2 VT420 Rear Connector Panel and Loopback Connectors . . . . 15
4-1 Set-Up Directory Screens. . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4-2 Screen Align Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4-3 Monitor Adjustment Controls . . . . . . . . . . . . . . . . . . . . . . . . . 45
4-4 Screen Test Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4-5 Rotation and Centering Adjustment. . . . . . . . . . . . . . . . . . . . 48
5-1 Set-Up Directory Screens... . . . . . . . . . . . . . . . . . . . . . . . . . 52
A-1 VT420 Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
C-1 VT420 North American Model . . . . . . . . . . . . . . . . . . . . . . . . 64
C-2 VT420 Worldwide Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Tables
1-1 VT420 Model Differences... . . . . . . . . . . . . . . . . . . . . . . . . . 3
2-1 Troubleshooting the VT420 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2-2 VT420 Self-Test Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2-3 VT420 Display Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . 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
Anode discharge t.ool
25-pin, RS-232 EIA loopback connector
Metric measuring tape
Two 6-pin, DEC-423 loopback connectors (modularjack)
Phillips screwdriver, number 2
Tuning wand
Video alignment tool
Part Number
29-24717-00
12-15336-00
29-25342-00
12-25083-01
29-11005-00
29-23189-00
29-26128-00
vii

viii About This Guide
Conventions
The following conventions are used in this guide:
Warnings
Cautions
Notes
Set-up features
ANSI keyboard keys
(LK401 or LK421)
PC keyboard keys
(LK443 or LK444)
ANSI keys (with PC
keys)
RS-232
PN
Provide information to prevent personal injury.
Provide information to prevent damage to equipment.
Provide general operatinginformation.
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.
Appear as normal text in a~
Example: Press the IRetum Ikey.
Appear as bold text in a§!.
Example: Press the la.turn Ikey.
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 4Enter~.
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 ofthe
different keyboards.

2 VT 420 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 38.4Kbits/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 3
• LK401 keyboard that includes
Right and leftI Alt Function Ikeys
RightI Compose Character Ikey
Lock and Hold LEDs
Table 1-1 VT420 Model Differences
Features
FCC Class B compliance
AC power cord:
Attached
Detachable with country-specific plug
Power supply ac input and line frequency:
120 V at 60 Hz only
100 V to 240 V (autoselect) at 50 Hz or 60 Hz
One 25-pin, RS-232 connector for the primary host, with
modem control
Screen rotation capability
National replacement character sets
Two Group Shift keys on the German LK401 keyboard to
replace the Compose Character keys
PC TERM mode
PC character sets
PC keyboard with 101 or 102 keys (LK443/LK444)
Short ANSI (UNIX style) keyboard with 74 keys (LK421)
Support for XPC communications protocol•
Driver support for the terminal in appropriate operating
systems
NA
No
Yes
No
Yes
No
No
No
No
No
No
No
No
No
No
No
WW
Yes
No
Yes
No
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
PC
Yes
No
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
•Refers to the remapping ofXON and XOFF points in PC TERM mode. After remapping,
XON is 651s 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.
4

Troubleshooting and Testing 5
•
•
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
Problems at Power-Up
Nothing appears
'Thrminal board.
on the screen.
The VT420 OK
The terminal was
display appears
powered down
and the bell tone with sessions
sounds, but the
enabled.
VT420 cannot
communicate with
host.
VT420
communication
port cable is loose.
Baud rate is
incorrect.
The on-line/local
feature is set to
Local.
Communication
port circuits are
faulty.
'Thrminal board.
Continuous bell An object is
sound at power
resting on the
up. keyboard
Keyboard.
The bell tone does Keyboard speaker
not sound, but
transducer
VT420 OK appears
on the screen.
• Section numbers follow the solution.
Solution•
1. Make sure all connectors on
the board are seated properly.
2. Replace the terminal board (3.3).
When power is restored to the
terminal, press F4
( lAltl Scroll Lock
Check the cable connection on the
rear of terminal.
Check the transmit and receive
speeds in the Communications
Set-Up screen.
Change the feature setting to On
Line in the Global Set-Up screen.
Run the RS-232 or DEC-423
loopback tests (2.2.4, 2.2.5, 2.2.6).
Replace the terminal board (3.3).
Remove all objects from the
keyboard.
Replace the keyboard (3.4).
Replace the keyboard (3.4).

Troubleshooting and Testing 7
Table 2-1 (Cont.) Troubleshooting the VT420
Symptom
Probable Cause
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.
The terminal
appears locked
and does not
respond to data
from the host.
There is
interference from
electromagnetic
energy.
'Turminal board.
CRT yoke harness
connector
'Turminal board.
CRT/yoke/bezel
assembly.
There is electrical
interference from
nearby devices.
The monitor is out
of alignment
'Turminal board.
Replace the
CRT/yoke/bezel
assembly
The~
(I Scroll Lock ~
key was pressed.
• Section numbers follow the solution.
Solution"
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.
Replace the terminal board (3.3).
Check and reconnect the connector
(3.2).
Replace the terminal board (3.3).
Replace the CRT/yoke/bezel
assembly (3.2).
Move the terminal away from nearby
electrical devices.
Adjust the monitor (Chapter 4).
Replace the terminal board (3.3).
Replace the CRT/yoke/bezel
assembly (3.2).
Press ~ q Scroll Lock I)to
resume scrolling.
In the Set-Up Directory:
1. Select Clear Comm to clear the
terminal.
2. Select Reset to reset the
terminal.

8 Troubleshooting and Testing
Table 2-1 (Cont.) Troubleshooting the VT420
Symptom Probable Cause
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-halfhour.
Phosphor retains
an imprint of
characters on the
screen when the
monitor is turned
off.
CRT saver feature
is activated.
CRT/yoke/bezel
assembly.
Character Display Problems
In local mode,
the screen
displays different
characters than
those typed.
Alternate
character set
selected.
Worldwide only:
Wrong keyboard
language selected.
Keyboard.
'Turminal board.
• Section numbers follow the solution.
Solution•
Press any key to restore the screen
display.
Replace the CRT/yoke/bezel
assembly (3.2).
Clear by selecting the Reset field in
the Set-Up Directory.
Check the keyboard language
feature in the Set-Up Directory.
Replace the keyboard (3.4).
Replace the terminal board (3.3).

Troubleshooting and Testing 9
Table 2-1 (Cont.) Troubleshooting the VT420
Symptom
Probable Cause
Character Display Problems
While on-line
with the host,
the screen
displays different
characters than
those typed. (The
terminal works in
local mode.)
When using the
copy and paste
feature, the
pasted characters
do not match
the characters
selected. (VMS
environment)
Messages are
garbled and
reverse question
marks appear on
the screen.
Other Problems
IF11I ( IEscl) does
not work when
running self-tests.
Incorrect transmit
and receive
speeds.
Incorrect bits
per character or
parity setting.
Stop bits setting
is incorrect.
'Turminal board.
Transmit speed
is set to 19200
baud, causing
the terminal to
send characters
faster than the
host computer can
receive them.
Baud rate is
incorrect.
XON/XOFF flow
control is not
enabled.
'Turminal board.
Incorrect mode
settings
• Section numbers follow the solution.
Solution*
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).
Using the VMS operating system,
type the following command at the $
prompt: SET TERMINAL/HOSTSYNC
Check the transmit and receive
speeds in the Communications
Set-Up screen.
Enable XON/XOFF fl.ow control
with the XOFF feature in the
Communications Set-Up screen.
Replace the terminal board (3.3).
Select Local in the Global Set-Up
screen. Select VTlOO Mode in the
General Set-Up screen.

1O Troubleshooting and Testing
Table 2-1 (Cont.) Troubleshooting the VT420
Symptom
Other Problems
After power-
up, one or more
keyboard LEDs
stay on. Or,
the LEDs do
not go through
their power-up
sequence.
The set-up cursor
does not appear.
When using a
modem, the
modem speed
select signals do
not work.
Worldwide
model: In PC
TERM mode, a
modem does not
work with the
terminal.
Probable Cause
Keyboard.
'Turminal board.
'Turminal board.
Cables.
'Turminal board.
The modem's XON
/XOFF settings
are incompatible
with the terminal.
• Section numbers follow the solution.
2.2 VT420 Self-Tests
Solution•
Replace the keyboard (3.4).
Replace the terminal board (3.3).
Replace the terminal board (3.3).
Check all cables and cable
connections. Replace the terminal
board (3.3).
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.
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 11
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 IEnterI and IReturn Ikeys 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
Power-up
Selected while the
VT420 is operating.
RS-232 port data lines
loopbackt
RS-232 port control lines
loopbackt
Printer port loopback
DEC-423 port loopback
Screen alignment pattern
Run all above tests, except
screen alignment pattern.
Prerequisites
None
Set-up
-Local mode
RS-232 loopback connector
RS-232 loopback connector
DEC-423 port loopback
connector
DEC-423 port loopback
connector
Set-up
-Local mode
See individual tests. All
loopback connectors must be
connected.
Sequence•
Tum the
terminal on.
Once:
ESC[4;ly
Continuously:
ESC[4;1;9y
Once:
ESC[4;2y
Continuously:
ESC[4;2;9y
Once:
ESCC4;6y
Continuously:
ESC[4;6;9y
Once:
ESCC4;3y
Continuously:
ESC[4;3;9y
Once:
ESC[4;7y
Continuously:
ESC[4;7;9y
ESC 8
Once:
ESC[4;0y
Continuously:
ESC[4;0;9y
• 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.