Digital Equipment VT50 User manual

VT50/VT52
Pocket Service Guide

E K-VT502-PG-001
VT50/VT52
Pocket Service Guide
digital equipment corporation • maynard. massachusetts

1st Edition, January 1979
Copyright © 1979 by Digital Equipment Corporation
The material in this manual is for informational
purposes and
is subject to change without notice.
Digital Equipment Corporation assumes no re-
sponsibility for any errors which may appear
in
this manual.
Printed in U.S.A.
The following are trademarks of Digital Equipment
Corporation, Maynard, Massachusetts:
DEC DECtape
DECCOMM DECUS
DECsystem-lO DIGITAL
DECSYSTEM-20 MASSBUS
UNIBUS
PDP
RSTS
TYPESET-8
TYPESETcll

CONTENTS
1 INTRODt:CTION
1.1 Purpose ..................................... .
1.2 Reference Documentation
..................... .
2 TROUBLESHOOTING
2.1 Troubleshooting Philosophy. . . . . . . . . . . . . . . . . . . . 2
3 REMOVAL AND REPLACEMENT
3.1 Removing and Replacing the EIA
or 20 rnA Adapter Card. . . . . . . . . . . . .. . . . .. . . .. 15
3.2 Removing and Replacing the Power Supply/
Monitor Assembly
Heat Sink Panel. . . . . . . . . . . . . 16
3.3 Removing and Replacing the Base
Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.4 Removing and Replacing the Character
Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 18
3.5 Removing and Replacing the Printer
Interface Option. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.6 Removing and Replacing the
RUT and
DP Modules .... . . . . . . . . . . . . . . . . . . . . .. . . . . . .. 20
3.7 Removing and Replacing the Anti-Static
Ground
Shield... . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.8 Removing and Replacing the Keyboard. . . . . . . . .. 22
3.9 Removing and Replacing the Power
Supply/Monitor Assembly. . . . . . . . . . . . . . . . . . . .. 23
3.10 Removing and Replacing the CRT
Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 26
3.11 Removing and Replacing the CRT Yoke. . .. . . . .. 27
3.12 Removing and Replacing the Electrolytic
Copier Option. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 28
3.13 Removing and Replacing the Transformer
Assembly. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . . . 29
iii

iv CONTENTS
4 ALIGNMENT AND ADJUSTMENTS
4.1 CRT Yoke Alignment ........................ .
4.2 Display Adjustments ......................... .
5 ACCEPTANCE
TEST PROCEDURES
5.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33
5.2 Terminal
Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.3 Copier Option Tests. . . . . . . . . . . . . . . . . . . . . . . . .
.. 36
5.4 Printer Interface Option Tests. . . . . . . . . . . . . . . . .. 36
6 INSTALLATION A:"oID OPERATION
6.1 Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7 PMK04 OPERATION
APPENDIX A CARE AND HANDLING
OF
CATHODE RAY TUBES
APPENDIX B REPLACEABLE
:\10DULES
AND ASSEMBLIES PARTS LIST
FIGURES
2-1 Troubleshooting Procedures Index ..............
2-2 ROM Chip Locations .........................
2-3 Jumper W7 Location ..........................
3-1 Removal and Replacement Guide ...............
3-2 Removing and Replacing the EIA or
20 rnA Adapter Card ..........................
3-3 Removing and Replacing the Power
Supply/Monitor Assembly Heat Sink Panel ......
3-4 Removing and Replacing the Base
Assembly
....................................
3-5 Removing and Replacing the Character
Generator and Optional Printer Interface
Module
......................................
3-6 Removing and Replacing the
RUT and
DP Modules ................................. '
3-7 Removing and Replacing the Keyboard
.........
3
14
15
16
18
19
20
22

CONTENTS v
3-8 Removing and Replacing the Power
Supply/Monitor Assembly .....................
23
,9
Discharging the CRT and Power Supply
Capacitors ...................................
24
3-10 Power Supply/Monitor Assembly
Capacitor Connections
........................
25
3-11
Installing the Power Supply/Monitor
Board Assembly
..............................
26
3-12 Removing and Replacing the CRT Assembly
.....
27
3-13 Removing and Replacing the Electrolytic
Copier Option
................................
28
3-14 Copier Power and Signal Connectors
............
29
3-15 Transformer Assembly Wiring Diagram
.........
30
4-1 Yoke Alignment ..............................
31
4-2 Display Adjustments ..........................
32
6-1
Function and Baud Rate Switch Settings .........
38
6-2 Power
ON/OFF Switch and Intensity Control
Locations
....................................
38
B-1
VT52 Replaceable Modules and
Assemblies/Parts List
.........................
46
C-l Physical/Functional Block Diagram .............
47
TABLES
2-1 Power on Troubleshooting Procedure. . . . . . . . . . . . 4
2-2 Character Display Troubleshooting
Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2-3 Display Troubleshooting Procedure . . . . . . . . .. . . . 9
~-4 Copier Option Troubleshooting Procedure .. .. . . . 11
l-5 Printer Interface Option Troubleshooting
Procedure. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2-6 Printer Interface Option Baud Rate Selection. . . . .
13
7-2 7-Bit ASCII Code. .. . . . . . . . . . . . . . . . . . . . . . . . . . 40

1INTRODUCTION
1.1 PURPOSE
The purpose of this Pocket Service Guide is to pro-
vide Field Service engineers and technicians with a con-
venient source of "memory jogger" reference
information for the VT50 and VT52 terminals. This in-
formation supplements detailed operation
and mainte-
nance information contained in the reference
documentation listed in Paragraph 1.2.
1.2 REFERENCE DOCUMENTATION
Document
VT52 DECscope Maintenance
Manual
DECscope User's Manual
PMK04 Operating and Service
Manual
Document No.
EK-VT52-MM-OOI
EK-
VT5X-OP-OOI
EK-PMK04-05-001

2TROUBLESHOOTING
2.1 TROUBLESHOOTING PHILOSOPHY
NOTE
Before attempting to troubleshoot the terminal ensure that
there actually
is a malfunction by checking that the unit is
properly set
up for operation with a host computer (Chap-
ter 6).
Figure
2-1 is an index to the troubleshooting pro-
cedures contained in Tables
2-1 through 2-5. Step-by-
step turn-on
and operating instructions are followed by
normal display indications.
If these indications are ab-
sent
or incorrect, refer to the corresponding tables for
troubleshooting information.
Possible equipment malfunctions are categorized by
abnormal symptoms. Corresponding causes are listed in
order
of probability. Corrective actions are limited
mainly
to the adjustments and/or substitutions of major
replaceable subassemblies suspected to be defective.
If after performing the off-line tests described
in this
chapter the terminal functions properly
but still does not
operate correctly when connected to a host computer,
verify
that portion of the terminal not checked by off-
line tests and the interface cabling with the PMK04
tester (Chapter 6).
2

TROUBLESHOOTING 3
YES
NOTE
NO
• BRIGHT SPOT CENTER OF
SCREEN
TABLE 21 STEP 5
• VERT OR HORZ LINE ONLY
TABLE 21 STEP 6
• RANDOM CHARACTERS
TABLE 22 STEP 4
• CHARACTE RS Du
NOT APPEAR
TABLE 22 STEP 1
• CHARACTERS TOO SHORT
TABLE 22 STEP 2
• I LLEGAL CHARACTERS
APPEAR
TABLE 22 STEP 3
• WRONG CHARACTERS
APPEAR
TABLE 22 STEP 5
• CHARACTERS DISTORTED
TABLE 22 STEP 6
• NO KEY CLICK
TABLE 22 STEPS 6 THRU 9
• DISPLAY FLICKERS
TABLE 23STEP 1
• DISPLAY OUT OF FOCUS
TABLE 2·3 STEP 2
• RASTER TOO SHORT
TABLE 23 STEP 3
• UNABLE TO
ADJUST RASTER
OR CHARACTER WIDTH
TABLE 23 STEP 4
• RASTER TOO NAR ROW
TABLE 23 STEP 6
• RASTER TILTED
TABLE 23 STEP 6
• RASTER TOO LARGE. ALL
CHARACTERS FUZZY
TABLE 23 STEP 7
IF PROBLEM PERSISTS,
RECHECK THE STEP
PERFORMED PREVIOUSLY
PAPER FAILS TO START
TABLE 24 STEP 1
COPIER STARTS BUT DOES
NOT PRINT
TABLE 24 STEP 2
COPIER PRINTS VERTICAL
LINE DOWN MARGIN
TABLE 24 STEP 3
COPIER IMAGE DIFFERS
TABLE 24 STEP 4
• NO CURSOR
RASTER PRESENT
TABLE 21 STEP 5
• CUs
• CURSOR AND
RASTER PRESENT,
ARCING HEARD
TABLE 2·' STEP 2
• UNABLE TO
ADJUST INTENSITY
TABLE 2' STEP 4
TYPED
TABLE 25 STEP'
VERIFICATION OF TERMINAL OPERATION CAN BE ACCOMPLISHED
BY PERFORMING THE ACCEPTANCE TEST PROCEDURES DESCRIBED
IN CHAPTER 5 AND PMK04 TESTS DESCRIBED IN CHAPTER 7
• PRINTER STARTS
UP BUT DOES
NOT
PRINT
TABLE 2·5 STEP 2
Figure 2-1 Troubleshooting Procedures Index

4 TROUBLESHOOTING
Table 2-1 Power On Troubleshooting Procedure
Symptom
I. No cursor
2. No cursor; no
raster
WARNING
Possible Cause
Unit not plugged
into power source
Intensity control
turned down
Blown fuse or
tripped circuit
breaker
Corrective Action
Plug unit into
appropriate source
of prime power.
Adjust intensity
control (Paragraph
6.2).
Replace fuse or
reset circuit
breaker.
No prime power at Restore source of
power receptacle prime power.
There are high voltages present in the power supply and CRT.
Ensure that the terminal power line is unplugged and the CRT
and capacitors are discharged (Figure3-9) before handling the
power supply
or CRT components. Ensure that ground connection
is made before discharging these points.
Defective
power
supply/monitor
assembly
Defective high
voltage
diode
assembly
Anode cap
disconnected
Anode clip
disconnected
Defective ON/OFF
switch
Replace
power
supply /monitor
assembly
(Paragraph 3.9).
Replace high
voltage diode
assembly (Figure
3-8).
Connect anode cap
at power supply
(Paragraph 3.2 and
Figure 3-8).
Connect anode clip
at CRT bell
(Paragraph 3.6 and
Figure 3-12).
Replace
transformer
assembly
(Paragraph 3.13).

TROUBLESHOOTING 5
Table 2-1 Power On Troubleshooting Procedure (Cont)
Symptom
WARNING
Possible Cause
Defective
RUT
module
Defective DP
module
Corrective Action
Replace
RUT
module (Paragraph
3.6).
ReplaceDP
module (Paragraph
3.6).
Use caution when handling the CRT to avoid shattering the tube.
The CRT is a vacuum device which can implode when broken.
Refer to Appendix A for
care and handling of CRTs before
proceeding further.
Defective
CRT
Replace CRT
(Paragraph 3.18).
Defective circuit Replace
breaker
transformer
assembly
(Paragraph 3.13).
Defective line filter Replace
transformer
(Paragraph 3.13).
Defective
power
Replace
transformer transformer
assembly
(Paragraph 3.13).
Loose
connector
Reseat connectors.
3. No cursor; no Defective
keyboard
Replace keyboard
raster
connector
(Paragraph 3.8).
Defective
keyboard
Replace keyboard
(Paragraph 3.8).
Loose ROMs on
Reseat ROMs in
RUT module
sockets.
Defective
RUT
Replace RUT
module
module (Paragraph
3.6).
Defective
DP
ReplaceDP
module
module (Paragraph
3.6).

6 TROUBLESHOOTING
Table 2-1 Power On Troubleshooting Procedure (Cont)
Symptom Possible Cause Corrective Action
4. Unable to Defective power Replace power
adjust CRT supply/monitor supply /monitor
intensity board board (Paragraph
3.9).
Defective CRT
Replace CRT
(Paragraph 3.18).
5. Bright dot in Defective power Replace power
center 0 f screen supply /monitor supply /monitor
board
board (Paragraph
3.9).
Defective yoke Replace yoke
(Paragraph 3.11).
CAlJTION
Minimize the time the bright spot
is allowed to remain on the
CRT to prevent damage to the screen's phosphorescent coating.
6. Horizontal or
vertical line only
displayed
7. Cursor and
raster presen
t;
arcing heard
Defective power
supply
/monitor
board
Defective yoke
Anode cap loose
Anode clip loose
Replace power
supply /monitor
board (Paragraph
3.9).
Replace yoke
(Paragraph 3.11).
Replace high
voltage diode
assembly (Figure
3-8).
Replace high
voltage diode
assembly (Figure
3-8).

TROUBLESHOOTING 7
Table 2-2 Character Display Troubleshooting Procedure
Symptom Possible Cause Corrective Action
1. Cursor and Baud rate
or Set switches to off-
raster present; function switch set line position
cannot display incorrectly (Chapter 6).
characters Character generator Reinsert character
card loose generator
(Paragraph 3.4).
Defective character Replace character
generator generator
(Paragraph 3.4).
Loose ROMs Reseat ROMs in
sockets.
Defective RUT
Replace RUT
module module (Paragraph
3.6).
Defective DP Replace DP
module module (Paragraph
3.6).
Defective keyboard Replace keyboard
(Paragraph 3.8).
2. Characters too Vertical size out
of
Adjust vertical size
short adjustment control (Paragraph
4.2.1).
Verticallinearity out
Adjust vertical
of adjustment linearity control
(Paragraph 4.2.3).
Defective power Replace power
supply
/monitor supply /monitor
board
board (Paragraph
3.9).
3. Illegal Defective character Replace character
characters generator card generatorcard
generated (Paragraph 3.4).
Defective RUT Replace RUT
module module (Paragraph
3.6).

8 TROUBLESHOOTING
Table 2-2 Character Display Troubleshooting
Procedure (Cont)
Symptom
4. Random
characters fill
screen when first
turned on
5.
Wrong
character
displayed when
typed
6.
No key clicks;
characters legal
but distorted
7.
:-;0 key clicks;
cursor present
8.
No key clicks
or cursor; raster
present
9.
No key clicks;
characters
Possible Cause
RUT /character
ROM/PROM chips
are incompatible
Defective
character
generator card
Defective DP
module
Defective RUT
module
Defective keyboard
Defective character
generator card
Defective RUT
module
Defective DP
module
Defective keyboard
Defective RUT
module
Defective interface
card
Corrective Action
Ensure
that
ROM/PROM chip
is A23002B4 series
(Figure 2-2).
Replace
character
generator card
(Paragraph 3.4).
Replace
DP
module (Paragraph
3.6).
Replace
RUT
module (Paragraph
3.6).
Replace
keyboard
(Paragraph 3.8).
Replace
character
generator card
(Paragraph 3.4).
Replace defective
RUT module
(Paragraph 3.6).
Replace defective
DPmodule
(Paragraph 3.6).
Replace defective
keyboard
(Paragraph 3.8).
Replace defective
RUT module
(Paragraph 3.6).
Replace defective
interface
card
(Paragraph 3.5).

TROUBLESHOOTING 9
Table 2-3 Display Troubleshooting Procedure
Symptom Possible Cause Corrective Action
I. Display
W7 jumper on RUT RemoveW7
flickers module
jumper on 60 Hz
units
or insert W7
jumper on 50 Hz
units (Figure 2-3).
2. Display
out of Yoke misadjusted Adjust yoke
focus (Paragraph 4.1).
Defective power Replace power
supply
/monitor
supply /monitor
board
board (Paragraph
3.9).
Defective
CRT
Replace CRT
(Paragraph 3.18).
3. Entire raster Vertical Adjust vertical
too short size/linearity
out of
size/linearity
adjustment control
(Paragraphs 4.2.1
or 4.2.3).
4. Unable to Defective power Replace power
adjust raster
or
supply/monitor
supply /monitor
character width board board (Paragraph
3.9).
5. Entire raster Horizontal size
out
Adjust vertical size
too narrow
of adjustment (Paragraph 4.2.1).
6. Entire raster Incorrect yoke Adjust yoke
tilted position (Paragraph 4.1).
7. Raster too Incorrect yoke Adjust yoke
large; all position (Paragraph 4.1).
characters
enlarged and
fULlY

10 TROUBLESHOOTING
A23002134
C=:3 ------ ROM CH" LOCATIO'
~CHARACTER
GENERATOR
Figure 2-2 ROM Chip Locations
Figure
2-3 Jumper W7 Location

TROUBLESHOOTING
11
Table 2-4 Copier Option Troubleshooting Procedure
Symptom Possible Cause Corrective Action
1. Copier fails
to Paperempty Install paper.
start when
COPY key is Defectivecopier Replace copier
typed (Paragraph 3.12).
Defective
DP Replace defective
module
DPmodule
(Paragraph 3.6).
Defective
RUT Replace defective
module
RUT module
(Paragraph 3.6).
Defective keyboard Replace defective
keyboard
(Paragraph 3.8).
Defectivepower Replace defective
transformer transformer
(Paragraph 3.14).
2. Copier starts
Dry paper Check paper
but does not
moisturecontent.
print Replace paper and
dampen wick
if
necessary.
Copier fuse blown Replace fuse (one
halfamp) on copier
logic board.
Defective copier Replace copier
(Paragraph 3.12).
Defective
DP Replace defective
module
DPmodule
(Paragraph 3.6).
Defective
RUT
Replace defective
module
RUT (Paragraph
3.6).
3. Copier prints Dry paper Dampen felt wick.
vertical line Clean helix wire.
along margin Replace paper.
4. Copier image Defective copier Replace copier.
differs from
screen image

12 TROUBLESHOOTING
Table 2-5 Printer Interface Option Troubleshooting
Procedure
Symptom Possible Cause Corrective Action
1. Printer fails to
Out of paper Replace paper
printwhen supply.
COpy key is
typed Defective printer Troubleshoot
printer as directed
in applicable
printer
maintenance
manual.
Defective printer Replace printer
interface card interface card
(Paragraph 3.5).
Defective
DP
Replace defective
module
DPmodule
(Paragraph 3.6).
Defective
RUT Replace defective
module
RUT module
(Paragraph 3.6).
Defective keyboard Replace defective
keyboard
(Paragraph 3.8).
2. Printer starts Printerinterface Set printer
but does not baud rate switches interface card baud
print set incorrectly rate switch
to
correspond to
printer
requirements.
Refer to Table2-6
for switch settings
and corresponding
baud rates.
Defective printer Troubleshoot
printer as described
in applicable
printer
maintenance
manual.