Tektronix 7904 User manual

COMMI`T`TED TO EXCELLENCE
PLEAS CHECK SCR CHANGE
INPCRMATION
AT THE READ C THIS MANUAL
.
CILL
COP'
SN
E260000®UP
IN ~F~U~~IUN
MANUAL_
Tektronix, Inc .
P .O . Box 500
Beaverton, Oregon

97077

Serial Number ____
070-2390-00

First Printing SEP
1977
Product Group 42

Revised MAY
1983

7904 (SN
8260000-UP)
Operators
Safety Information

.............,....,...    ,...
iv
Service Safety
Information .......... ... . .................,..,.,,,,.,,..
.
vi
SECTION 1

GENERAL INFORMATION

Page
Introduction .......................................
.......... . . .... .1-1
Installation ....

............................
. . . . ................... 1-1
Initial
Inspection ..........................
....................... 1-1
Operating Power
Information ................ ................,.,, . , , . 1-1
Operating Voltage ....................
. . ........... . .... . . . . . . .... 1-2
Operating Position ............. . . ...
............. ..... . ........... 1-3
Operating Temperature

........ ................  
1-3
Repackaging for
Shipment ... ... . ................ ... . , .  ,
1-3
Specification ...... .... . . ....................
....................... .1-4
System Electrical Specification ............... . ... , . 
1-12
Standard Accessories

.............. . . . . ............... 
1-14
SECTION
2

OPERATING INSTRUCTIONS
Preliminary Operation

................... 
2-1
Plug-In
Units ...................................
. . . .............. . . . . 2-1
Installation
of Plug-In Units

................,., .    , 2-1
Controls and Connectors .....................,.. .,.,.        2-1
Functional Check

............................
........ . . . . . . .... . ....
.2-4
Set-Up Information ........... .
. . ... ........ . . . ................... 2-4
Display
Focus ............... ............
........................ 2-4
Trace Alignment

. . .... ... . ............... ..... . .................
.2-4
Graticule
Illumination

. ......... . . ... ..,.....  .  , 2-4
Controllllumination
..... . . . . .....  ,..  ,
.2-5
Vertical Deflection System ..............,...  .  
,
2-5
Horizontal Deflection System ..............,.....   , . 
2-5
Triggering .....................................................
.2-7
Readout ......................................................
.2-7
Beam Finder
.....................................
. ...... . ...... .2-7
Calibrator .....................................
. ................ 2-8
Z-Axislnput
................................ . ..................
.2-8
Simplified Operating Instructions
................. . ....,..,.,,,,,,,,,,,,,, 2-g
Single-Trace Display
........... . .....
. . . . . ........................
2-8
Dual-Trace Display ...........
. . . . . . .............................. 2-9
Dual-Sweep
Display ...... . ........................................
2-10
Dual-Trace--Dual-Sweep
Display . ............,.,.  .  , 2-10
Independent-Pairs
Display ...................... 
2-11
Delayed Sweep-Single Trace
Display ....................,,..,,.,,,,.,,
2-11
Delayed Sweep-Dual Trace .........,......,....   , .  
2-12
X-Y
Display ..............................
.... . .... . . . ..... . . . . . . 2-12

7904 (SN B260000-UP)
SECTION 2

OPERATING INSTRUCTIONS
(cont)

Page
Detailed
Operating Information
......................~~~-~~~-~-----~----~~
2-13
Intensity Controls

................................................
2-13
Crt
Phosphor Protection

.......................~~~~~~-~~--~~--~~...
2-13
Display
Focus
. . . . ..... .........................................
.2-13
Astigmatism Adjustment
......... . . ... .......~~~~~-~~---~----~--~~~.
2-13
Y'race Alignment
Adjustment

. .......... . .... ......~~~~~~~~~--~----~~
2-13
Graticule .............
. .... ............. ......................
.2-14
Light Filter .......................
.........
. . . ..................
2-14
Beam Finder ........................
.
... ......... . .... . . . .
. .... .2-14
Controllllumination
........................ .--~~~~~~----~------~~
.2-15
Readout . . . ....................................
..
.... .... . . ... .2-15
Remote Readout .. .
. ...........................................
. .2-16
Display
Photography ..... . .... ....................................
2-16
Vertical and
Horizontal Mode
Switch Logic

..... . ..........~~~~~~~--~~~- -
2-17
Vertical
Trace Separation ............... . . . . .....~~~~~~~--~--~~-~~~ ~
2-19
Trigger
Source

........ ..................
.......................
.2-20
X-Y Operation . . .............
... . . . .............
... . .............
2-21
Intensity
Modulation

................. ... . ~ ~~~~~~~-------- - ----
-~~~
2-21
Raster
Display ............................
.......................
2-22
Calibrator ......................................
. . . . . ..... . .
.... 2-22
Signal Outputs

........................................ .
. ...... . . 2-23
Probe Power
Connectors .... . ..................~~~~-~~~------~-~~~~
2-23
Applications
.......... . . . . . . ...................................
.2-24
THE REMAINING
PORTION OF THIS TABLE OF
CONTENTS LISTS THE
SERVICING INSTRUC-
TIONS
. THESE
SERVICING INSTRUCTIONS
ARE FOR USE BY QUALIFIED
SERVICE PERSONNEL
ONLY .
T
O
AVOID ELECTRIC SHOCK OR
OTHER PERSONAL INJURY, DO
NOT PERFORM
ANY
SERVICING OTHER THAN THAT
DESCRIBED IN THE
OPERATORS INSTRUCTIONS UNLESS
YOU
ARE QUALIFIED TO DO SO .
SECTION 3

CIRCUIT DESCRIPTION
Introduction ...............
. .... ........ . ...
.......................
.3-1
Logic
Fundamentals

. . ..............
. ...
..... . . . .....................
.3-1
Block
Diagram

..............................
........ . .
..... . ...... . .3-2
Main
Interface .................................
. . ..
.................. 3-2
Front-Panel
Interconnect .................. .~~~~--~~~~~~----~~--~---~~~
.3-5
Logic ........... .... . . ...........................................
.3-5
Trigger Selector

...........
. . . . ......................................
3-24
Readout System

............
. ..... . . . . . .............................
.3-27
Vertical Amplifier ....
... . . ................
.
.. .
........................
3-46
Horizontal
Amplifier ............... ...... .~~~~~~~~~~~---~~--~--~--~~
. .
.3-49

7904 (SN 8260000-UP)
SECTION
3

CIRCUIT DESCRIPTION (cont)

Page
Output Signals and Calibrator

...... ............. ........................
3-52
Converter/Rectifiers . . . . ..... ... . ......... .............................
3-54
Low-Voltage Regulators . . . . ......... . . ... ..............................
3-59
CrtCircuit . . . . . . . ............... . . ... ............................ . .3-62
SECTION 4

MAINTENANCE
Preventive Maintenance

. . . ............................. . .... . . ... .....
4-1
Cleaning ...... ... . .............................. . . . . ..... . ..... 4-1
Visual Inspection .
. . . ............   .  .,........
. . , . .  ,..,..  . 4-2
Semiconductor Checks

........................... ............... . .4-2
Periodic Electrical Adjustment

...................... ............... . .
4-2
Troubleshooting . . . ............................
. . . ............... ... .4-3
Troubleshooting Aids ........................ ....... . .... . . .... ....
4-3
Troubleshooting Equipment .................. ........ . . . . . ... ... ....
4-5
Troubleshooting Techniques

................ ......... ... . ... . .......
4-5
Troubleshooting the High-Efficiency Power-Supply Unit ...... . . . . ........... 4-8
Corrective
Maintenance ........................ ...... . . ................ 4-13
Obtaining Replacement
Parts ................ ... . . . .................. 4-13
Soldering Techniques

................. ...... ......................
4-73
Component Removal and Replacement .... ...... .......................
4-14
Adjustment After Repair .......... . ... ...... .............,..........
4-27
SECTION 5

PERFORMANCE
CHECK AND ADJUSTMENT
Preliminary Information ....... . .... ............ .......,,..,....,...,, ..
5-1
Adjustment Interval . . . . . . . . . .......... ........................,., .
5-1
Using this Procedure . ...... . ........ ............................ . .
5-1
Test Equipment Required . . . ......... . . . ............................ ....
5-1
Test Equipment Alternatives . ..... . . . . . ..........,.......... . . ... .... 5-2
Performance Check/Adjustment
Procedure Index ............... . ..... . .... .... 5-5
Setup Procedure . . .....
. . ... ..................... . . . . . .......... .5-6
SECTION 6

OPTIONS
SECTION 7

REPLACEABLE ELECTRICAL PARTS
SECTION 8

DIAGRAMS and CIRCUIT BOARD
ILLUSTRATIONS
SECTION 9

REPLACEABLE MECHANICAL PARTS
CHANGE INFORMATION

7904 (SN 8260000-UP)
OPERATORS SAFETY
INFORMATION
The following general safety
information applies to all
operators and service
personnel . Specific warnings will be
found throughout the manual
where they apply and
should be
followed in each instance .
Grounding the Instrument
This
instrument is safety class 1
equipment (IEC
designation) . All accessible conductive
parts are directly
connected through the
grounding conductor of the power
cord to the grounding
contact of the power connector
.
WARNING

statements identify conditions or
practices which could result in personal injury or
loss of
I ife .
CAUTION

statements identify
conditions or prac-
tices which could result
in damage to the equipment or
other property .
The power-input plug must be inserted only
into
a
mating receptacle with a grounding contact
. Do not defeat
the grounding connection
. Any interruption of the groun-
ding connection can
create an electric-shock hazard .
Refer to qualified
service personnel for verification of
adequate
protective grounding system to which this
instrument
is to be connected .
The word DANGER on the equipment identifies areas
of immediate hazard which could result in personal injury
or loss of life .
For electric-shock protection, the
grounding connec-
tion must be made before
making connection to the
instrument's input or output
terminals .
The following safety symbols may appear on the
equipment .
CAUTION-Refer to manual
DANGER-High voltage
Protective ground (earth)
terminal
Do Not Remove Instrument Covers
To avoid electric-shock hazard,
operating personnel
must not remove the protective
instrument covers . Com-
ponent replacement and
internal adjustments must be
made by
qualified service personnel only .
Other warning symbols where they apply
.
WARNING
AC Power Source and Connection
Do Not Remove CRT° Implosion Shield
This instrument operates from a single-phase power
source . It has a three-wire power cord and a two-pole,
three-terminal
grounding-type connector
. The voltage to
ground (earth) from
either pole of the power source must
not exceed the maximum rated operating voltage, 250
vol ts .
Do not remove the clear
plastic implosion shield
covering the crt
face
plate . This crt implosion shield
provides protection to the operator from crt implosion .
Before making connection to the power source,
deter-
mine that the instrument is adjusted to
match the voltage
of the power source, and
has
a
suitable two-pole, three-
terminal grounding-type connector . Refer any changes to
qualified service personnel .
Do Not Operate in Explosive
Atmosphere
To avoid explosion, do not operate
this instrument in an
explosive atmosphere
unless it has been certified forsuch
operation
.
iv

7904 (SN 8260000-UP)
Use the
Proper Fuse
Refer fuse replacement to qualified service personnel
only
.
To avoid fire hazard, use only the fuse specified in
the
parts list for your instrument and which is identical in
the following
respects
:
Exercise Care with Intensity Level
Crt phosphor damage can
occur under adverse con-
ditions . Avoid any condition where an extremely bright,
sharply focused
dot exists on the crt . Also, remember that
fhe light filter reduces the apparent
light output from the
crt .
Prevent Instrument
Damage
A .

Type : Slow blow, fast blow, etc
.
B . Voltage rating : 250 V, etc .
C . Current rating .
Plug-in units should not
be installed or removed
without first turning the instrument power off, to prevent
instrument damage .
Operating-Power Consideration
To
prevent damage to the instrument always check
the
LINE VOLTAGE
SELECTOR switch, located on the rear of
the instrument,
before connecting the instrument to the
supply circuit .

7904 (SN 8260000-UP)
SERVICE SAFETY INFORMATION
The following are safety precautions which appear in
the servicing information sections of this manual . This
Service
Safety Information is in addition to the Operators
Safety Information given previously .
WARNING
Do Not Service
Alone
Do
not attempt internal service or adjustment
unless
another person, capable of rendering
first aid and
resuscitation, is present .
Exercise Care
When Operating Instrument with
Covers
Removed
Dangerous potentials
exist at several points
throughout this
instrument . When the instrument is
operated
with the covers removed, do not touch exposed
connections or components . Some
transistors have
voltages present on their cases . Disconnect
power before
cleaning the instrument or replacing
parts .
Disconnect the instrument from the
power source and
allow the line storage capacitors to
discharge before
removing the power-unit
cover . The line storage
capacitors remain
charged with high-voltage do for
several minutes
after the line power is disconnected
unless they
are manually discharged . A warning-indicator
neon bulb, located on the Power-Supply Inverter
board,
flashes when this stored voltage exceeds
about 80 volts .
Do not remove the power-unit
cover while this light is
flashing .
Use extreme
caution when troubleshooting in the
power-supply
unit, to avoid electric shock . Stored do
potentials on the Power-Supply Inverter circuit board
remain long after the instrument is
disconnected from the
power source . Verify
that the power-cord plug is dis-
connected and that the
line storage capacitors (C1216 and
C1217)
are completely discharged before attempting any
repairs or ohmic measurements . (A
warning-indicator
neon bulb, located on the Power-Supply
Inverter board,
flashes when this storage
voltage exceeds about 80 volts .
However, simply because the neon bulb is not flashing
does not mean that the capacitors are fully discharged .)
Disconnect Instrument Power
To avoid electric-shock hazard, always
disconnect the
7904 from the power source
before removing or replacing
components .
To avoid electric-shock hazard, disconnect
the instru-
ment from the power source
before soldering .
Silicone Grease Handling
Handle silicone grease with care . Avoid
getting the
silicone grease in your eyes . Wash hands thoroughly
after
use .
CRT Handling
Use care when handling a crt . Breakage of the
crt
causes a high-velocity scattering of glass
fragments
(implosion) . Protective clothing and safety
glasses should
be worn . Avoid striking the crt on any object
which might
cause it to crack or implode
. When storing a crt, place it in
a
protective carton or set it face down in a protected
location on a smooth surface with a soft mat under the face
plate .
Avoid Excessive Moisture
Exercise Care When Servicing Power Unit
The
power supply unit has been Tested at the
factory fo
ensure safe operation . Improper repair of
This unit can
result in hazardous potentials on
the instrument chassis .
Do not remove the plate insulator,
block insulator, or
transistor shield from
the heaf-sink . (See the exploded
view
drawing of the power supply unit for the location of
these components .)
Circuit boards and components must be dry before
applying power to prevent damage from electrical arcing .
Exercise Care When Checking Diodes
When checking diodes, do not use an ohm-meter scale
that has a high internal current, since high currents may
damage the diodes under test
.
vi

7904 (SN 8260000-UP)
Exercise Care When Soldering on Multi-Layer
Boards
Several of the circuit boards
in
the 7904 are multi-layer
type boards with a conductive path laminated between the
top and bottom board layers . All soldering on these boards
should be done with extreme care to prevent breaking the
connections to this center conductor . Only experienced
maintenance personnel should attempt repair of these
boards
:
A2-Main Interface, A4-Logic, AS--Trigger
Selector, A7-Vertical
interface, A12-Cap-Rectifier .
Use Proper Cleaning Agents
Avoid the use of
chemical cleaning agents which might
damage the plastics used in this instrument . Use
a
non-
residue type of cleaner, preferably isopropyl alcohol,
totally denatured ethyl alcohol, or TP35 . Before using any
other type of cleaner consult your Tektronix Service
Center or representative .
Do Not Use Pin Sockets for Connection Points
Exercise Care When Handling CRfi Anode Lead
Do
not touch any components with the crt anode lead
until it is fully discharged .
The spring Pension of the pin sockets ensures a good
connection between the circuit board and the pin . This
spring
tension can be destroyed by using the pin sockets
as
a
connecting
point for spring-loaded probe tips,
alligator clips, etc .
Universal Euro
220 volt/50 Hz
Rated 16 ampere
North American
120 volt/60 Hz
Rated 15 ampere
(12 amp max ; NEC)
Australian
240 volt/50 Hz
Rated 10
ampere
North American
240 volt/60 Hz
Rated 15 ampere
(12 amp max ; NEC)
23617-01
Power plug options .
REV A DEC 1980

7904 (SN
B260000-UP)
2394 ~ 3
7904 FEATURES
The TEKTRONIX 7904 Oscilloscope is a solid-state, high
performance instrument designed for general purpose
applications . The 7904 features a crt with small spot size and high writing
rate . Graticule area is 8 X 10 cm . Additionally, the
instrument
includes a readout system providing crt display of alphanumeric
information from the plug-ins, including
deflectior7 factor, sweep
rate, and other encoded parameters .
The instrument's high vertical bandwidth (500 MHz),
and four plug-in compartments which accept 7-series plug-in
units, form
a
highly
flexible measurement system .

Section 1-7904 (SN B260000-UP)
INTRODUCTION
INSTALLATION
The Instruction Manual contains both operating and
servicing information for the 7904 Oscilloscope .
Section 1-General Information
;
contains safety infor-
mation, instrument description, electrical specifications,
environmental
characteristics, standard and recommend-
ed accessories, and packaging for shipment instructions .
Section 2-Operating Instructions ; contains informa-
tion relative to operating and checking the instrument
operation
.
Initial Inspection
This instrument was inspected
both mechanically and
electrically before shipment . It should be free of
mars or
scratches and should
meet or exceed all electrical
specifications . To confirm this,
inspect the instrument for
physical damage incurred in transit and test the electrical
performance by following the Operating Instructions in
Section 2 and
Performance Check Procedure in Section 5
of the
Instruction Manual
.
If there is damage or deficiency,
contact your local
Tektronix Field Office or represen-
tative .
Section 3~-Circuit Description ; contains basic and
general circuit analysis that may be useful for servicing or
operating the instrument
.
Operating-Power Information
Section 4--Maintenance ; describes routine and correc-
tive maintenance procedures with detailed instructions for
replacing assemblies, subassemblies, and individual com-
ponents .
This instrument can
be operated
from either a 115-volt
or 230-volt nominal supply source, 48 to 440 Hz .
Section 5-Performance Check and Adjustment ; con-
tains procedures to check the operational performance
and electrical characteristics of the instrument .
Procedures also include methods for adjustment of the
instrument
to meet specifications .
Section 6-Instrument Options ; contains a description
of available
options and locations of incorporated infor-
mation for those
options .
To prevent damage to the instrument, always
check
the LINE VOLTAGE
SELECTOR switch located on
the rear of the instrument
before
connecting
the
instrument to the supply circuit .
Section 7-Replaceable Electrical Parts ; contains in-
formation necessary
to order replaceable parts and
assemblies related to the electrical functions
of the
instrument
.
Section
8-Diagrams and Circuit Board Illustrations
;
includes detailed
circuit schematics, locations of
assembled boards
within the instrument, voltage and
waveform information, circuit
board component locators,
and locations of adjustments to aid
in performing the
Adjustment procedure .
WARNING
AC POWER
SOURCE AND CONNECTION . This
instrument
operates from a single-phase power
source
. It has a three-wire power cord and two-pole,
three
Terminal
grounding-type plug . The voltage to
ground (earth) from either pole of
the power source
must not exceed the maximum
rated operating
voltage, 250 volts .
Section
9-Replaceable Mechanical Parts ; includes
information necessary
to order replaceable mechanical
parts and shows exploded
drawings which identify
assemblies .
Before making connection to the power
source,
determine
that the instrument is adjusted to match
the
voltage of the power source, and has a suitable
two-pole, three-terminal
grounding-type plug . Refer
any changes to qualified
service personnel .