Gould OS300 Service manual

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OS300 20MHz
DUAL TRACE
OSCILLOSCOPE
INSTRUCTION
MANUAL
Operating
a dService
Manual
•} GOULD

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•}
GOULf
IMPOR
T
ANT
Warranty
is
valid on/
,t
equipment with Gou/~ I you register the serial numb
f
Electronics & Electrical Prod,
Use the attached nc ers o
your
card
for
this purpose.
PRINTED 3-82
COPYRIGHT 1982
Registration Will:
l.
2.
Insure
full
protection un
Prevent
billing
for
repa1/!~;arranty
conditions.
covered by warrant
y.
Mode/ No.
0
~~
0
---
Mode/ No.
----
-----
Serial No.
---
---
OS300 20MHz
DUAL
TRACE
OSCILLOSCOPE
INSTRUCTION
MANUAL
The
information
contained herein
is
the
exclusive
property
of
Gould Inc., except
as
otherwise
indicated and shall
not
be
reproduced in whole
or
in part
without
explicit
written
authorization
from
the company. The
distribution
of
this
material outside the company may occur
only
as
authorized
by
t~e company in
writing
.
All
information
contained in this manual
is
the
latest
product
information
available at the
time
of
printing. The right
is
reserved
to
make changes
at any
time
without
not
i
ce.
Gould Inc., Instruments Division
3631
Perk
ins A
venue
.
Cl
e
vel
and
,
Oh
io
44114
1ST PRINTING
PRINTED IN U.S.A.

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WARRANTY
AND
SERVICE
FACILITIES
Gould Oscilloscopes are warranted for a period
of
one
year from date
of
shipment
to
original purchaser.
They
are warranted
to
conform
to
the applicable published
specifications
in
effect at the time
of
shipment,
and
to
be
free from any defects
in
material
or
workmanship.
LIABILITY
OF THE
GOULD
INSTRUMENTS
DIVISION
UNDER SUCH
WARRANTY
IS
LIMITED
TO SERV-
ICING OR REPLACING
DURING
THE
WARRANTY
PERIOD
AT
THEIR
OPTION,
ANY
DEFECTIVE
PARTS
EXCE
PT
COVERS, PROBES OR FUSES
AND
DOES
NOT INCLUDE
CALIBRATION
AND
MINOR
MAIN
-
PACKING
INFORMATION
If the unit
is
to
be returned for service, it must be
adequately packed as follows:
a) Seal the unit in an oversize plastic bag.
b) Pack the bagged unit
into
a heavy
duty
cardboard
box
.
The
box
must
have a
minimum
of
2 inches
of
cushioning
on
all
six sides, so
that
the unit fits snugly.
c) Any accessories
or
instruction manuals must
be sealed into a separate plastic bag and
packed with a minimum
of
2 inches
of
cushioning between
the
instrument and
the accessories.
TENANCE
AS
OUTLINED
IN OPERATING MANUALS.
IN NO
EVENT
SHALL
THE GOULD INSTRUMENTS
DIVISION
BE
LIABLE FOR
CO
L
LATERAL
OR CON-
SEQUENTIAL
DAMAGES.
Units are
to
be returned transportation prepaid by the
buyer. The Gould Instruments Division will have the right
of
final
determination
of
the cause and existence
of
a
defect
under
this warranty. This warranty shall not
apply to
any
products
which have been subjected to
misuse, improper installation, repair, alteration, neglect,
accident,
inundation,
fire
or
operation outside their
published maximum ratings.
d) Before sealing the
box
with packing tape,
ensure
that
an official packing note
is
inserted, giving full details
of
sender's
name, address and telephone number,
instrument
type
number
and serial
number,
plus an indication
of
the reason
for
return,
and/
or
fault conditions,
if
applicable.
e) Properly label and address the outside
of
the
box
.
t)
Notify Gould
in
advance
of
shipment and ship
prepaid by United Parcel Service or equivalent.

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ATLANTA
INSTRUMENTS DIVISION
1710
Wilwat Drive
Suite D
Norcross, Georgia
30093
Phone (404)
441-5556
BOSTON
INSTRUMENTS DIVISION
129 Middlesex
Turnpike
Burlington, Massachusetts O
1803
Phone:
(617)
272-0750
BAY AREA (CA)
INSTRUMENTS DIVISION
25936
Eden Landing Road
Hayward, CA
94545
Phone: (41 S)
887-1300
CHICAGO
INSTRUMENTS DIVISION
I001
Oakton
Street
Elk Grove Village, Illinois
60007
Phone:
(312)
640-4380
Gould
Inc
In
struments
Div
35129
Curtis
Blvd
Eastlake
Oh
44094
Phone:
(216)
361-3315
DAYTON
INSTRUMENTS DIVISION
4668
Gateway Circle
Kettering, Ohio
45440
Phone:
(St
3)
433-9586
DENVER
INSTRUMENTS DIVISION
1500
West
Hampden
Avenue
Unit
1C
Englewood, Colorado
80110
Phone
:
(303)
781-4473
DETROIT
INSTRUMENTS DIVISION
23775
Northwestern
Southfield, Michigan
48075
Phone:
(313)
355-0900
HOUSTON
INSTRUMENTS DIVISION
I
0500
Northwest Freeway
Hou ton, Texas
77092
Phone:
[phone]
LA
HAM
,MD
INSTRUMENTS DIVISION
5900
Princess
Garden
Parkway
Lanham/
Seabrook
, Maryland
20706
Phone:
(301)
459-7350
SERVICE
CENTERS
LOS ANGELES
INSTRUMENTS DIVISION
2525
Campus Drive
Irvine, California 9271 S
Phone: (213} 639-7301
ORLANDO
INSTRUMENTS DIVISION
772
Northlake
Avenue
Altamonte
Springs, Florida 32701
Phone
(305)
830-0695
PHILADELPHIA
INSTRUMENTS DIVISION
GSB Building
Belmont & City Line Avenue
Bala
Cynwyd,
Pennsylvania 19004
Phone
:
(215)
839-7066
PITTSBURGH
INSTRUMENTS DIVISION
Campbells
Run
Road
Parkway West
Pittsburgh, Pennsylvania 15205
Phone
:
(412)
923-2160
SADDLEBROOK
INSTRUMENTS DIVISION
74 Kenney Place
Saddle
Brook,
New Jersey
07662
Phone
:
(201)
845-0220
SEATTLE
INSTRUMENTS DIVISION
The
Commons
Bldg. Suite C-155
I
200
I
12th
Avenue NE
Bellevue, Washington
98004
Phone:
(206)
453-8100
TORONTO
ALLAN CRAWFORD ASSOC., LTD
6503
Northam
Drive
Mississauga,
Ontario
, Canada
Phone:
678-1500
EUROPE
GOULD INSTRUMENTS S.A.F.
57 rue St. Sauveur
91160
Ballainvilliers,
France
Phone: [phone]
GOULD INSTRUMENTS DIVISION
Roebuck Road
Hainault, E sex, England
Phone
:
01
-
500
-
1000
GOULD INSTRUMENTS DIVISION
Dieselstrasse
5-
7
D-64S3 Seligenstad
t,
West Germany
Phone:
06182-3107

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Contents
SECTION
1
Introduction
SECTION
2
Specification
SECTION
3 Operation
3.1
Connection
to
the supply
3.2 Obtaini
ng
a Trace
3.3 Setti
ng
up the Y channels
3.4 Display Modes
3.5 Timebase and X Expansion
3.6 Trigger
3.7
Additional
Facilities
SECTION
4
Circuit Description
4.1 General
4.2 The Y
Amplifier
and Beam Switch
4.3 The Trigger Circui
ts
4.4 The Timebase Generator and
X
amplifier
4.5 The Mode
Control
Circuits and
Calibrator
4.6 The Power Supplies and C.R.T.
Circuits
1.1
2.1
3.1
3.1
3.1
3.1
3.2
3.2
3.2
3.3
4.2
4.2
4.2
4.3
4.3
4.4
4.5
SECTION
5
Maintenance
5.2
5.1
General 5.2
5.2 Access 5.2
5.3 Fault Findi
ng
5.3
5.4 Setti
ng
-
up
Procedure 5.5
SECTION
6
Component
Lists
and
Circuit
Diagrams
6.1
SECTION
7 Guarantee
and
Service Facilities
7.1
ILLUSTRATIONS
Fig.
1 Block Diagram 4.1
Fig
. 2
Internal Assembly -
top
view 5.1
Fig.
3
Internal Assembly -
bottom
view 5.3
Fig.
4
Circuit
Diagram, Y
Ampl
ifi
er
6.8
Fig
.
5 Circuit Diagram, Ti
mebase
&
Tr
i
gger
6.9
Fig.
6 Ci
rcuit
Diagram, Power Supply
and C.R.T. Circuits 6.
10
Fig.
7
Mechanical Views
6.11

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Introduction
The OS300
is
a versatile general purpose dual trace
oscilloscope intended for general laboratory, industrial,
servicing and educational applications. The full 8 x 10cm
rectangular tube provides a bright display against the
calibration graticule.
It features two identical input channels with a maximum
sensitivity
of2mV
/cm and a bandwidth from D.C.
to
20MHz. These channels may be displayed separately or
together in dual trace mode. Alternatively they can be
added
or
subtracted for sum
or
difference display. The
timebase ranges from 0.2s/cm
to
O.Sµs/cm
and
ax
10
expansion facility extends this to S0ns/cm. Independent
variable sensitivity and sweep rate controls are provided.
I.
I
Section 1
Particular
attention
has been paid
to
trigger performance,
with D.C. and A.C. coupling available and a bright-line
free-run facility
to
enable trace location in the absence
of
trigger. An active T.V. synch separator
is
provided for
those working with video waveforms.
The OS300 includes many facilities such
as
a IkHz
calibrator, a D.C. coupled Z modulation input and a
trace rotation control, usually found only on the more
expensive instruments.
This compact instrument
is
readily portable. The
internal construction
is
based largely on a single printed
circuit board assembly
to
provide easy access for main-
tenance and minimum cost
of
ownership.

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Specification
DISPLAY
8 x 10cm rectangular mono-accelerator c.r.t. at 2kV
e.h.t. Trace Rotation
by front panel preset.
VERTICAL DEFLECTION
Two identical input channels CHI and CH2.
Bandwidth (-3dB)
d.c.
to 20MHz (2Hz to 20MHz on a.c.)
Sensitivity 2mV/cm to lOV/cm in 1- 2- 5 sequence.
Accuracy ±3 %
Variable Sensitivity >2 ,5 :I range allows continuous
adjustment
of sensitivity from 2mV/cm to 25V/cm.
Input Impedance IM!1/28pF approx.
Input Coupling DC-GND-AC
Input Protection 400V d.c. or pk a.c.
DISPLAY MODES
Single Trace CHI or CH2
Dual Trace Chopped or Alternate modes automatically
selected
by the T.B. switch. Between 0.5µs/cm
and 0.2ms/cm the ALTERNATE MODE
is
selected. While on ranges slower than 0.2ms/cm
CHOP MODE
is selected. The CHOP frequency
is S00kHz.
Add CHI and CH2 added to give the algebraic sum of
the two channels.
Invert CH2 CH2 may be inverted. When used in conjunc-
tion with Add mode it gives the algebraic
difference
of the two channels.
X-Y CH2 input gives Y deflection and CHI input gives
X deflection.
Bandwidth (-3dB) DC to 1MHz with less than 3° phase
shift at 50kHz.
HORIZONTAL DEFLECTION
Timebase 0.5µs/cm to 0.2sec/cm, 18 ranges in 1- 2- 5
sequence
Accuracy ±3 %, (to 200ns/cm)
X Expansion x 10 push button gives fastest speed of
50ns/cm. Accuracy ±3% (S0ns/cm range ±5%)
Variable Sweep >2 .5 :1 allows continuous coverage
from 0.5µs/cm
to 0.5sec/cm.
TRIGGER
Variable level control with Bright Line ON/OFF facility.
With Bright Line
on, the timebase free-runs when
insufficient signal (20Hz -20MHz)
is present or when the
selected level
is outside the range of the input signal.
Source Internal CHI or CH2 or External.
Slope+ or -.
Coupling DC , AC or TV (active sync. separator with
line/frame selected by T.
B. switch between 50 and
I0Oµs/cm).
Sensitivity
Internal: DC coupled 2mm to 2MHz, 5mm to 20MHz.
AC coupled 2mm, IOH z- 2 MH z.
5mm , 4Hz- 20MHz.
2. 1
Section 2
External: DC coupled IO0mV to 2MHz, 400mV to 20MHz.
AC coupled IO0mV, IOHz to 2MHz,
400mV, 4Hz
to 20MHz.
External Input Impedance 100k!1/10pF approx.
External Input Protection 250V d.c. or pk, a. c.
ADDITIONAL FACILITIES
Calibrator IV , 2% squarewave at approx. IkHz.
Ramp Output Approx. +3 .5V ramp from 5k!1.
Z Mod. Input DC coupled, 2V visible mod. sensitivity,
+40V cut-offsensitivity, input impedance
10k!1/10pF approx.
Maximum input lO0V d.c.
or pk, a.c.
SUPPLY
I00V, 120V, 220V and 240V ± I 0%
45 to 440Hz approx. 40VA.
SAFETY
Designed for I.E.C.348 Cat. 1.
OPERATING TEMPERATURE RANGE
0 to +50°C (+15 to +35°C for full accuracy)
DIMENSIONS
140 X 305 X 460mm
WEIGHT
6kg approx.
ACCESSORIES SUPPLIED
Manual P.N. 80-OS3 00
Mains lead P.N. 402001
OPTIONAL ACCESSORIES
Probe
Kit PB12
A passive probe kit with switched XI and XI0
attenuations. XI 0 attenuation input impedance is
l0M!1/11.5pF.
Probe Kit PB13
A XI0 passive probe with 1.5m of cable. Input
impedance IOM!1/l l .5pF.
Viewing Hood
P.N.41179.
Trolley
Type TR ?. General Purpose.
Protective Carrying Case
P. N. 42610 Astrong case which completely
encloses the oscilloscope with 3 thicknesses
of
padding covering the front panel.
Tube Option
Long pe rsi stance c.r.t. P7 phosphor.
Rack Mount Kit
P.N. 4500 7 0.
Front Cover
P.N. 4502 40 .

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Operation
INTERNATIONAL
SAFETY
WARNING
(as
required
for
1.E.C.
348
Class
I)
This instruction manual contains
information
and
warnings which must be observed
by
the user
to
ensure
safe
operation
and retain
the
apparatus
in
a safe
condition.
The
instrument
has been designed for
indoor
use within
the
specified limits
of
temperature.
It should
not
be switched
on
if
there are obvious signs
of
mechanical damage and it should
not
be used
under
wet
conditions.
GROUNDING
The instrument must be
operated
with
a protectiveground
connected
via
the
appropriate (yellow/green)
conductor
of
the
supply cable. This
is
connected
to
the
instrument
before
the
line and neutral supply
connectio
ns when
the
supply socket
is
inserted
into
the plug
on
the
back
of
the
instrument.
If
the
final
connection
between
the
instru-
ment
and the supply is made elsewhere,
the
user must
ensure
that
the
ground
connection
is
made before line
and neutral.
If
any
supply cable
other
than
that
supplied with
the
instrument
is
used, it must carry an adequate protective
ground
conductor.
Any
interruption
of
the protective
earth
conductor
inside
or
outside the
instrument
is
likely
to
make
the
instrument dangerous.
Intenti
onal
interruption
is
prohibited.
Signal connections
into
the
instrument
should
be
connected
after
and disconnected before
the
protective
ground
connection
is
made, i.e. the supply lead must be
connected at all times that signal leads are
connected.
LIVE
PARTS
The
instrument
is
safe
to
operate
with
the
covers fitted
and these must
not
be removed
under
normal usage. The
covers
protect
the user from live parts and
they
should
be removed only
by
suitably qualified personnel for
maintenance
or
repair purposes. (see maintenance
section).
VENTILATION
The
OS300 relies
on
convection cooling and must
not
be
operated in a position which restricts the external circu-
lation
of
air.
3.1 CONNECTION TO
THE
SUPPLY
I . Before connecting the OS300
to
the
supply, check
that the supply range switches are set
to
suit the
supply voltage to be used and that the correct fuse
is
fitted . Note that the fuse has
to
be changed when
switching between the I
00V
and
220V
ranges.
The
switches and fuse holder are
mounted
on
the
ba<.:k
panel
of
the
instrument.
Do
not
operate
the range
selection switches while the
OS300
is
switched on.
3.1
Section 3
3.2
OBTAINING
A TRACE
I. After
connection
to
the
supply, switch
on
by turning
the INTENSITY
control
clockwise away from the
OFF
position. Check
that
the
POWER indicator
L.E.D. lights.
2. Set
the
:
MODE switch
to
CHI
CHI Y shift
control
(vert. arrows)
to
approx. mid
setting.
CHI
VAR
SENS control fully clockwise
to
the
C
AL
position.
CHI
input
coupling switch
to
GND.
BRIGHT LINE
button
out
(ON)
.
X
MAG.
button
out
(XI)
X
shift
control
(horiz. arrows)
to
approx
. mid
setting.
TIME/CM switch
to
5µs.
A horizontal trace should appear
on
the screen
as
the
INTENSITY
control
is
advanced.
3. Adjust
the
INTENSITY
control
to
obtain
a display
of
the
required brightness.
4.
Adjust
the
FOCUS
control
to
obtain
a sharply
defined trace.
5.
Adjust the CH
I
Y shift
control
and the
X
shift
control
tocentralize the trace
on
the
screen.
6. Adjust
the
TRACE
ROTATE preset
control
if
neces-
sary
to
align
the
trace
with
the
center
graticule line.
It
may be necessary
to
re-adjust this
control
only
when
the
instrument
is
re-positioned
as
the beam
deflection can be affected
by
earths magnetic field or
other
sources
of
magnetic radiation.
NOTE:
The
OS300
should
not
be
operated
close
to
sources
of
alternating magnetic field such
as
large
transformers as these
may
interfere
with
the trace.
3.3 SETTING
UP
THE Y CHANNELS
I . Using a coaxial
input
signal lead,
connect
a signal
to
the
CHI
or
CH2
input
socket,
2.
For
(a)Direct
connection
of
the
input
signal, set the
associated AC-Ground-DC slide switch
to
DC.
(b)
Capacitive coupling
of
the
input
signal through
an internal 0 .
lµF
400V
capacitor, set
the
slide
switch
to
AC
.
NOTE: When examining low amplitude a.c. signals
superimposed
on
a high d.c. level, the slide
switch should
be
set
to
AC and the sensitivity
of
the
Y
amplifier increased
as
in
(4).
3.
To
locate the base line, set the slide switch
to
the
c;
D s
etting
.
At
this setting, the
input
signal
is
open
<.:ir<.:uit
and the input
to
the amplifier
is
connected
to
ground.
4.
To
select sensitivity, set the VOLTS/
CM
switch
to
the
required range.
For
calibrated
operation,
the
VARiable
SENSitivity
control
should be set fully clockwise
to

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Operation
the CAL position. This control can be used however
to
reduce the gain
of
the relevant amplifier and
obtain any intermediate sensitivity between the
calibrated switched ranges. To set
to
any particular
calibrated sensitivity, the actual variation from the
calibrated range can be set
by
viewing the CAL
I
Volto/pon
the0.IV/cm
or0
.2
V/cm ranges.
If
the
VAR SENS control
is
not moved, the sensitivity will
differ from the calibrated value by approximately the
same proportion on all settings
of
the VOLTS/CM
switch.
To minimi
ze
pick-up at sensitive settings, it
is
essen-
tial
to
ensure that the ground lead connection
is
near
to
the signal point.
5. For vertical movement
of
the trace, adjust the Y shift
controls (identified by the vertical arrows).
6. Any trace movement under no-signal conditions,
when the setting
of
the VOLTS/DIV switch
is
altered,
can be overcome by adjustment
of
the relevant preset
front panel balance control.
This control will only need adjustment at infrequent
intervals. Before adjusting the BAL control however,
ensure that the input coupling switch
is
set
to
GND.
No adjustment should be made until a minimum
of
15
min. warm-up time has lapsed after switch-on, or
immediately after any large change
of
ambient
temperature.
3.4 DISPLAY MODES
The MODE switch determines the form
of
the display.
I.
For single trace display
of
one Y input against the
timebase this switch should be set
to
CHI or CH2 and
the input signal applied to the appropriate input
connector.
2. For dual trace simultaneous display
of
both
Y inputs
against the timebase, this switch should be set
to
DUAL. Two modes
of
beam switching are used and
selected automatically by the sweep rate selected by
the TIME/CM switch. The alternate mode
is
used at
fast sweep rates between 0.2ms/cm and 0.5µs/cm.
At the slower rates from 0.2s/cm
to
0.5ms/cm the
chop mode operates at approx. 500kHz.
3. In the ADD mode, the single trace generated against
the timebase
is
the algebraic sum
of
the CHI and CH2
deflections.
If
the INV CH2
button
is
operated the direction
of
Y
deflection for that channel
is
reversed .
If
used in the
ADD mode, this facility allows the difference
between the CHI and CH2 inputs to be displayed.
The
INV
CH2
button
has no effect on the polarity
of
internal CH2 trigger.
When
examining small differences between large
signals, the effect
of
small errors between the sensit-
ivities
of
the two channels can be overcome by first
connecting one input to
both
channels simultaneously
3
.2
Section 3
and adjusting one
or
other
of
the VARiable SENSitivity
controls
to
obtain a straight line.
4. In the
X-Y
mode, the timebase
is
disabled and the
CH2 input
is
displayed
as
the vertical Y deflection
against the CHI input displayed
as
horizontal, X
deflection. The CHI shift control
is
inoperative and
X position
is
determined only by the X shift control.
The XI 0
MAG
facility
is
also inoperative. X deflection
sensitivity being determined by the CHl controls
only. The X bandwidth
is
limited to
1MHz
and
relative phase shift between X and Y deflections may
exceed 3° above 50kHz.
3.5 TIMEBASE AND X EXPANSION
The sweep speed
of
the internal timebase
is
determined
by
the setting
of
the TIME/CM switch. The VARiable
SWEEP speed control should be set fully clockwise in
the CAL position for calibrated operation
of
the time•
base. This control
is
used
to
slow the sweep rate to
obtain any intermediate sweep rate, between the
calibrated ranges.
For horizontal shift
of
the trace, adjust the X shift
control (horizontal arrows). If close examination
of
any
portion
of
the trace
is
required,
Xl0
expansion can be
introduced by operation
of
the
MAG
button
. This
provides
an
effective trace length
of
l00cm and any
portion
of
this may be selected for viewing on the screen
by operation
of
the X shift control.
3.6 TRIGGER
The timebase may be triggered internally from the CHl
or
CH2 signals by operation
of
the corresponding
TRIGGER
button,
irrespective
of
whether the selected
channel
is
being displayed. Alternatively, the timebase
may be triggered from an external signal applied to the
EXT TRIG sockets when both CHl and CH2 buttons are
operated simultaneously.
Trigger
will
occur at a level on the signal which may be
set by the TRIG LEVEL control with the slope deter-
mined by the ±
button
. When this
button
is
out,
it will
occur
on
a positive-going transition
of
the signal through
the trigger level. When it
is
pushed in, trigger will occur
on
the negative-going transition. Normally triggering can
be obtained from internal deflection signals greater than
2mm
pk/pk
up to about 2MHz but the sensitivity
reduces to about 1cm
pk/pk
at 20MHz. Corresponding
external sensitivity
is
0.25V
pk/pk
to 2MHz and 1.25V
pk/pk
at 20MHz.
With A.C. coupling, the low frequency sensitivity
reduces to Icm
pk/pk
at about 2Hz.
The Ext Trig input impedance
is
approx. I00k/1
0pF
and
c.:are
should be taken not to apply more than 250V d.c.
or pk, a.c. to this socket.
When the BRIGI
IT
LINE
button
is
out or O , the time-
base will free run
in
the absence
of
a correct trigger
sig
nal, to display a bright line or
un
synchronizeddisplay

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Operation
until the level control is adjusted and/or the amplitude
of the trigger signal is increased. This free-run action in
the absence
of correct trigger, helps in finding the trace
and leads
to ease of operation. If the timebase is
required to free-run continuously, the LEVEL control
should be set to either end of its rotation.
It is expected that the BRIGHT-LINE OFF mode will
be selected only when the instrument
is to be used to
display signals
at repetition rates less than 40Hz or faster
than 2MHz. This will prevent additional free run sweeps
from occurring between correctly triggered low
frequency sweeps or erratic high frequency operation.
The coupling
of the trigger signal may be selected as a.c.
or d.c. by operation of the corresponding TRIGGER
button . When both are pressed, an active synch.
separator circuit
is introduced to provide line or frame
triggering for video waveforms. Field trigger occurs at
low sweep rates up
to IOOµs/cm and line trigger is auto-
matically selected on fast sweep rates from SOµs/cm.
The trigger polarity should be selected for the polarity
of the synch. pulses. At least 2mm pk/pk of synch. pulse
amplitude
is required with internal triggering or 0.25V
with external.
Summarizing the use
of the trigger controls for most
applications:
a) With BRIGHT LINE ON
(button out) , select the
trigger source
CH I, CH2 or EXT and the coupling
required, a.c.
or d.c.
b) Select the trigger slope +
or -and adjust the trigger
level control to obtain a stable trace, starting at the
required point on the waveform.
3.7 ADDITIONAL FACILITIES
l . Calibrator
This
output pin on the front panel provides a positive
going 1V flat topped square wave at approx. IkHz.
It can be used to check the sensitivity of the instru-
ment
or to set to any particular calibrated sensitivity
(see section 3.3.4). The rise time
is approx. 2µs and
the
output impedance is approx. 470il, providing
approx. 2.3mA when shorted to ground.
The CAL
output may be used also to set up passive
probes (see section 3.7.
4) .
2. Ramp
Output
This 4mm socket on the rear panel provides a d.c.
coupled positive-going ramp generated
by the
J.J
Section 3
timebase of approx. +3.SV pk from an impedance of
approx. Sk ohms. If a lower output level can be
tolerated, distortion
of fast ramp output signals due
to capacitive loading can be avoided by adding resis-
tive loading to attenuate the signal.
3. Z mod
This socket
on the rear panel allows modulation of
the brightness. The input is d.c. coupled into approx.
I
Okil/ lOpF. The sensitivity at normal brightness
settings requires about 2V
to provide visible
modulation. Approx. +40V
is required to provide full
trace blanking.
Care should be taken
not to apply more than I OOV
d.c. or pk, a.c. to this socket.
4.
Use of the Passive Probe
A XI Opassive probe may be used to extend the
voltage range and increase the
input impedance of the
Y amplifiers. The
input resistance of a Y channel is
I OM ohms, shunted by approximately 28pF . The
effective capacitance
of the input lead must be added
to this and the resultant impedance can often load
the signal source. Therefore it is advisable to use a
IM ohms, XlO probe such
as PB12 or PB13. This
reduces the input capacitance and increases the input
resistance, at the expense of a 1 OX reduction in
sensitivity. The probe inserts a shunt RC network in
series
to form a 10:I attenuator with the input RC
of the Y channel. To obtain a flat frequency response
it
is necessary to adjust the capacitance of the probe
to match the input capacitance of the Y channel
as follows:
I. Set the Y channel VOLTS/CM switch
to 20mV,
the TIME/CM switch to
SOOµs and trigger from
the appropriate channel.
2. Connect the probe to the CAL socket.
3. Adjust the probe compensation
to obtain a level
trace, i.e. flat
top without overshoot or under-
shoot.
5. Camera
A camera may be used with the oscilloscope to record
waveforms. This facility
is particularly useful at slow
timebase sweep rates. Suitable cameras utili
zi ng
Polaroid film may be obtained from Shackman and
hand held against the tube face. Other oscilloscope
cameras may be used
but suitable adaptors must be
obtained and should be discussed with the camera
manufacturer.

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Circuit Description
To aid component location, circuit references have been
allocated in the following general pattern.
99 Components
not mounted on printed
circuit boards.
100 199 Components
mounted on the attenuator
assemblies.
200
299 Pre-amplifier and Ramp Generator
components
mounted on the daughter
board.
300 -399 Y Pre-amplifier and Beam Switch
components
mounted on the main board.
400 -499 Y Amplifier and Y
Output Amplifier
components mounted on the main board.
500 599 Timebase and X
Output Amplifier
components mounted
on the main board.
600 699 Trigger circuit
components mounted on
the main board.
700 799 Power supply and Modulation Circuit
components on the main board.
4.1 GENERAL
Referring to the block diagram (Fig. I) signals applied to
the CHI and CH2 input sockets pass into their respective
attenuators and amplifiers. The VOLTS/CM switch
controls the gain
of the pre-amplifier in steps of 1.2.5
sequence to cover the ranges from 2mV/cm to 0.1 V/cm
and a + I
00 attenuator is introduced before the
amplifier
on the ranges 0 .2 V/cm to IOV/cm.
The Variable Gain control adjusts the amplifier gain to
give I to 2 .5 times reduction of gain on all settings of
the Volts/cm switch. The fast electronic beam switch
selects either the CHI or the CH2 signal to be amplified
further and passed
to the Y deflection plates of the c.r.t.
A sample of each signal is taken and passed to the trigger
switch bank where selection
of CH I, CH2 or Ext trig
source
is made.
The selected signal
is amplified and passed to the
Schmitt trigger, the
output of which clocks the timebase
bistable "
on" . The ramp generator then begins to
generate its linear ramp, which, after passing through the
X amplifier, is applied to the X deflection plates of the
c.r.t. and drives the electron beam linearly across the
tube face. A portion
of the signal from the ramp
generator
is fed back to the hold-off circuit, shutting the
gate to prevent any further pulses from the Schmitt
trigger from reaching the timebase bistable during the
ramp period. When the ramp has reached the necessary
maximum level, the timebase bistable
is reset, and the
ramp
is quickly returned to its quiescent state. A time-
constant in
the hold-off circuit retains this signal to
inhibit another ramp from being initiated for a short
period, until the ramp timing capacitor
is discharged
fully . Thus a ramp
is generated at a rate set by the
TIME/CM switch when the trigger signal reaches a pre-
determined level. This ramp sweeps the beam across the
4
.2
Section 4
c.r.t. face , returns and waits for the next input cycle to
reach the set trigger point, so producing subsequent
ramps. The timebase bistable
is connected to a blanking
amplifier whose function
is to turn on the electron beam
during the sweep and blank it
off during the fly-back
and subsequent waiting period.
At fast sweep rates for a dual trace display, the
TIME/CM switch automatically selects the alternate
sweep mode
of control for the beam switch. At the end
of each sweep, the signal from the timebase reverses the
state
of the beam switch bistable, causing alternate
displays of the CH I and CH2 signal on successive sweeps
of the timebase. At slow sweep rates, the chop mode is
selected, when the chop multivibrator free runs indepen-
dently, causing the beam
to switch on chop between
CHI and CH2 levels during the sweep.
A signal from the multivibrator also blanks the trace
during each switching transitition. With CHI
or CH2
only selected, the beam switch bistable is held to select
that channel only.
In the X-Y mode, the bistable is held
to select CH2 as the Y deflection signal, while an
additional switch diverts the
output from the CH I pre-
amplifier, to
the X output amplifier as the X deflection
signal in place of the normal ramp signal. The blanking
amplifier
is held in the bright-up state. When TV trigger
mode
is selected, an additional synch. separator circuit is
introduced into the signal path leading into the trigger
amplifier.
4.2 THEY AMPLIFIERS AND BEAM SWITCH
These circuits are shown in Fig. 4.
The attenuators and pre-amplifiers
of channel I are
identical to those of channel 2 and accordingly only
channel I
is described.
The input signal
is applied to SKA and then to the
attenuator via the 3 position slide switch, SIOI. This
allows the input signal
to be directly coupled through in
the
DC position or coupled via C105 in the AC position.
In the central GND position, the input signal from SKA
is left open circuited while the input to the attenuator
is grounded.
On the most sensitive ranges, 2mV/cm to IOOmV/cm,
the VOLTS/CM switch, S102, couples the signal through
directly
to the pre-amplifier and the network resistor,
RNIO!c, provides the input impedance. On the
remaining ranges, SI
02 introduces RI 01 a into the signal
path to form a 100:I
attenuator with RN!Ol bin
parallel with RNI0lc .
High frequency compensation
of the attenuator is pro-
vided by CIOI and CI04 while Cl02 with C106 allows
the input capacitance
of the attenuator to be set to
equalise that of the unattenuated ranges.
Diodes, D201 and D202 with R
207, provide input
protection by limiting the input voltage appled to the
amplifier
to the voltages of zencr diode, D203 and the
positive supply line.

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Circuit Description
The input stage
of
the pre-amplifier
is
formed
by
the
f.e.t. source followers, TR201 and
TR202,
and
emitter
followers,
TR204
and
TR203.
Unbalance in this stage
is
corrected
by
the BAL control
potentiometer,
R301 .
The input stage drives the divider
network
, RN201 . The
VOLTS/CM switch second wafer, S201, selects the
necessary
output
, either directly via RN201 on the 2mV
or
200mV
ranges,
or
attenuated
by
2.5,
5, 10, 25
or
50
times
on
the subsequent ranges. This network presents a
constant
output
impedance and further
attenuation
is
introduced
by
the
shunt action
of
the VARIABLE
sensitivity control, R217. The resultant signal
is
amplified by the integrated amplifier, IC301 . The ampli-
fier gain
is
determined by R309 and the preset, R302.
The differential
output
is
balanced
by
the bias through
R308 from the preset, R307.
The differential
output
from IC301
(CHI)
or
from
IC35 l (CH2)
is
selected
by
the beam switch
as
the
input
for the subsequent shunt feedback amplifier stage
formed
by
TR401,
TR402
. The signal input currents are
defined by R3 l6 and R3 l7 and are summed with the Y
shift currents defined by
R3
l8 and
R3
l9 from the
CH
I
shift control, R3 I5. The corresponding
components
for
channel 2 are R366, R367, R368, R369 and R
365.
Channel 2 only differs for channel I
by
the addition
of
the double pole changeover switch, S301, which reverses
the
output
signals from IC351 in the INVERT mode.
The beam switch
is
formed by the 8 diode gate, D301,
D302,D303
,
D304,D351,D352
,D353,D354.The
relative control potentials from IC501 allow either the
signal current from IC301
and/or
IC351
to
reach the
bases
ofTR401
and
TR402
, or divert those currents
from the bases.
The
outputs
from the differential shunt feedback ampli-
fier stage formed by TR401 and
TR402,
are fed
to
the
gounded emitter amplifier stage,
TR403
and
TR404
.
This in turn feeds the differential cascode Y ou
tput
stage
TR405,
TR406,
TR407
and
TR408
to drive the Y
deflection plates
of
the c.r.t.
High frequency compensation
of
the
output
amplifier
is
provided by networks between the emitters
of
TR403
and
TR404
and those
of
TR405
and
TR406.
Adjust-
ment
of
this compensation is
by
C402 and C405.
4.3 THE
TRIGGER
CIRCUITS
These circuits are shown in Fig. 5.
The Trigger Source switches, S502 and S503, connect
the required trigger signal via the Trigger Coupling
switches, S504 and S505, to
the
trigger buffer amplifier
formed
by
TR601 and
TR602
. S502 selects the differen-
tial CHI signal
via
R313 and R314
frow.
IC301 (Fig.
4)
.
S503 selects the equivalent CH2 signal via R363 and
R364 from IC35
l.
Where
both
S502 and S503 are
selected,
both
of
the above signals are disconnected and
the single-sided
input
from the EXT TRIG input socket
SKC'
is
selected.
4.3
Section 4
When the
AC
coupling switch, S504,
is
out
, the trigger
signals are directly coupled-through,
but
when this
switch
is
in,
AC
coupling
is
introduced via C603 and
C604 (C60I on External). TR601 and
TR602
form a
differential buffer amplifier with the
DC
balance
controlled by the
TRIGGER
LEVEL control, R602.
The differential
output
from this stage
is
applied
to
the
comparator, IC602, which has positive feedback applied
by
R623
to
form a Schmitt trigger circuit. The change-
over switch, S506, reverses the
output
from TR601 and
TR602
to determine the trigger slope.
When
both
S504 and S505 are
"in"
(AC and
DC
in for
TV mode), the
junction
of
R603 and C610
is
connected
to
the -
11
V supply. D601 and D608 are brought into
conduction while D602 and D604 are reverse biased.
This diverts the
output
of
the trigger amplifier away
from IC602, into
TR605,
which amplifies the positive
tips
of
the video waveform only. TR605
is
prevented
from saturation
by
feeding back the peak detected
synch. pulses
via
TR607
and
TR606
to the emitter
of
TR605
. These pulses are amplified by IC60 Ib and
applied via R6 I7 and D603 to the Schmitt trigger,
IC602.
IC60la
is
used
in
conjunction with S504 and
S505
to
disable the synch. separator when
AC
or
DC
is
selected.
At the fast timebase sweep speeds, S 262a
is
open and
TR603
is
cut
off. However, at speeds
of
I00µs/cm and
slower, R608
is
connected to +
11
V and TR603
is
switched on. This effectively grounds C609 to introduce
an
RC
integrating time constant into the synch. pulse
signal time path in the TV mode to separate
out
frame
trigger.
4.4 TIMEBASE GENERATOR
AND
AMPLIFIER
The square wave trigger
output
from IC602
is
applied
(with d.c. bias
of
zener diode, D605)
as
the clock to the
D type
TTL
flip-flop, IC50Ia. A positive-going trigger edge
will
cl~k
the bistable, driving Q low.
In
the waiting
state,
Q
was high (+4
.5
V), turning on
TR
26I
via
R507
and R262, holding the input, and hence the
output,
of
the operational amplifier, IC26 I at 0V. This timebase
amplifier
is
connected
as
a direct voltage follower.
When the trigger signal sends
Q
of
IC50Ia low, the time-
base clamp transistor,
TR26
I,
is
turned off. Part
of
the
constant current generated
by
TR264
flows through the
resistor network, RN272, to charge C263 at a constant
rate. The resultant positive-going linear ramp voltage
generated at the
input
of
IC261
is
buffered by that
amplifier
to
generate the low impedance ramp
output.
The timebase range switch S262, selects the tap point
on the network, RN272,
to
vary the ramp slope
in
the
1.2.5 sequence over a range
of
three decades. On all fast
sweep ranges,
TR262
is
biased-Off
but
on ramps
0,5ms/cm and slower, S262c connects R263
to+
11
V.
TR
262
is
turned
on
and C264
is
effectively connected
in
parallel with C263 to slow the sweep rate 1000 times.

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Circuit Description
The constant current into the ramp generator is derived
from the current mirror circuit formed
by TR262 and
TR264. The variable gain control, R261, provides an
approximate 3: I range of variation in this current, R506
provides a preset calibration control on the slow sweep
rates, only when S262c is closed.
When the ramp reaches its maximum level the negative
bias, introduced
by R5 21 and RS 19, is overcome and
TR503 turns on, driving the reset input
of the timebase
bistable low. As the bistable switches, Q returns high and
TR26I conducts to discharge the timing capacitor(s) and
the sweep
is complete. However, a hold-off action takes
place
to inhibit trigger signals during sweep and this
remains for a short period after a sweep
to ensure that
the ramp potential
is fully reset before the next sweep
can be triggered. As the ramp goes positive, D506
conducts to charge C502, reverse biasing D503 and turn-
ing on TR502. A.!_ the end of sweep when the timebase
bistable is reset, Q goes low and the D input follows via
the action of D508 and RSI I. The ramp output returns
rapidly toward 0V but TR502 remains in conduction for
a period determined by C502 and RS 18 . Only when
TR502 turns off can RS 16 and D507 take the D input
high for the bistable to respond to the next clock input.
TRS0I acts in a way similar to TR262 (described above)
to introduce additional hold-off time through CS0I on
the slower half of the timebase ranges.
The bright line facility causes the timebase to free-run in
the absence of trigger signals. The square wave output
from the Schmitt trigger, IC602, is coupled via C615
into the peak detector diodes, D606 and D607, to
generate a positive-going signal into the - ve input of
IC601c driving its output negative. In the absence of
such trigger signals for a period determined by C6 I8
with R627 and R626, the output of IC601c goes
positive. When TR502 turns
off at the end of the hold-
off period, D509 conducts to turn on TR504, driving
the set input low
to initiate another sweep.
This free-run condition is removed as soon as IC60 Ic
detects an output from the Schmitt trigger. It can be
inhibited also with a positive bias via R625 if the
BRIGHT LI EOFF switch, SS0I , is operated.
The X output amplifier
is formed by the shunt feedback
stage
ofTR509/TR5 l I driving single sided into the
amplifier stage, TRS I3 and TRS 14. The collector out•
put
of this stage drives the X deflection plates of the
c.r.t. directly from TRS I4 and
via emitter follower
TRS 15 from TRS I3. The gain introduced by
TR509/TR511
is defined in the x!0 magnification mode
by the input resistance, R539, and the feedback
resistance, R552, with the preset, R553. In this mode
the transistor switch, TRS 12 , is biased off. However, in
the normal xI magnification mode S507 is open and the
current in R548 turns on TRS 12 , introducing R544 with
preset, RS IJ , as additional feedback to reduce the gain
of the amplif1er accordingly.
The Xshift control. R271 , introduces an additional bias
input
via R54I and emitter follower TR506, through the
potential divider R569/R545 .
4.4
Section 4
4.5. MODE
CONTROL CIRCUITS
The display mode is controlled by S261 (Fig. 5) which
defines the state
of three control lines according to the
following table.
Mode
LI L2
L3
Q Q
ICS0lb
X-Y
+I IV 0 +I
IV
L H
CHI 0
+IIV 0 H L
Dual
+I IV +!IV
0 Switching
CH2 +I IV 0 0 L H
Add 0 0 0 H H
These lines in turn control the function of the beam
switch and other necessary signal switching.
Section 4.2 described the signal switching action
of the
beam switch diodes, D30 I
to D304 and D35 l to D354.
These are controlled by the Q and Q outputs of the
beam switch bistable, ICS0!b.
In the CHI mode LI is
open, allowing R5 25 to take the set input of the bistable
low, Q
is high and Q is low, selecting the channel I signal
for Y display. In the CH2 and X-Y modes, LI is at + 11 V
and RS14 takes the set input high but L2 is open and
R524 takes the reset input low
to reverse the bistable
and select the channel 2 signal.
In the Add mode, both LI and L2 are open so that both
set and reset are applied to the bistable, Q and Qare
high and both channel signals are added into the shunt
feedback stage
of the Y amplifier (Fig. 4) . In this mode
only, LI, L2 and L3 are open, removing the bias through
D401 , D402 or D403 and defined by R401 and R402
via D405 and D406. This offsets the additional bias
introduced by the selection
of both channel signals.
Only in the X-Y mode , L3 is held at +I IV toturnon the
diode gate of DS 15 and DS 14, so coupling the channel I
preamplifier signal
of IC 301, via TR506 and R547 into
the X output amplifier. At the same time D504 conducts
to turn
off the gain switching transistor, TRS 12, thereby
selecting x IO X magnification irrespective of the
position
of S507.
DS0I conducts allowing current througl1 R509 to turn
on TR261, clamping the ramp generator so that no
signal is fed into the X amplifier via R539. Finally,
current througl1
RS 12 turns on TR504, holding the
timebase bistable set "on " to provide continuous bright-
bright-up
of the trace.
In the Dual mode, both LI and L2 are held at + 11 V so
that the beam switch bistable, ICS0I , is free of set or
reset signals. Thus it can respond to clock signals and as
its D input is connected to its Q output its state reverses
on each clock input .
On the fast sweep ranges (0.2ms/crn and above), the
dock input is derived via emitter fo!lower, TR505,
dir
ec tly from the Q nutput of the timebase bistable.
Thus the heam switch operates in the alternate mode.
The Y deflection
is switched between cha nn els at the

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Circuit Description
end
of
each sweep.
TR507
and
TR508
form a free-
running
emitter
coupled multivibrator
but
on
the above
ranges, S262 -
is
open such
that
R
534
is
disconnected
and the multivibrator is paralyzed.
On the slow ranges (0.5ms/cm and below), R534
is
connected
to
+
11
V and the multivibrator runs. During
each sweep period, the multivibrator provides
continuous
clock
inputs
to
the beam switch bistable so that the
beam deflection signal
is
made
to
chop
between the two
channel signals. The beam switching
is
inhibited
between sweeps
as
the
emitter
follower,
TR505
, clamps
high the clock
input
to
the beam switch bistable.
In
all
modes
but
Dual,
L1
or
L2 are low and
D5
l2
or
D5
l 3
conducts
to
inhibit the action
of
the multivibrator.
IC60ld
is
used for the
!kHz
calibrator.
It
is
connected
as
an oscillator with positive feedback
via
R629 and
negative feedback via R633. This
wi
th C617 defines the
frequency
as
approx.
!kHz
. The
output
is
buffered
by
the transistor switch, TR
604,
which defines the
calibrator
output
amplitude
via
the potential divider
of
R638 and R643 with preset, R641.
4.6 THE POWER SUPPLIES
AND
C.R.T. CIRCUITS
These circu
its
are shown
in
Fig. 6. The following d.c.
supplies are generated in the power supply circuit from
secondary windings
on
the supply transformer,
Tl.
+210V, +I
IV
, +7V, - 5V, -
11
V, - 1850V.
The +210V line
is
used primarily
in
the
X
and
Y
output
amplifiers. The -1850V line
is
the cathode supply for
the c.r.t. In addition, a +5V line is generated
in
the time-
base area from the +
11
V line
by
IC552 (Fig. 5).
The incoming a.c. supply from the supply
connector
,
PLM
,
is
switched
by
SI and fused by FS I before
reaching the two supply range switches, S2 and S3.
S2 connects the
two
primary windings
of
TI
in
series
or
in
parallel for 120V
or
240V operation while
S3
selects
the necessary tap for IO0V or 220V operation.
The
output
from the 2 10V secondary
is
bridge
re
ctified
by the four bridge connected diodes, D722
to
0725,
into the reservoir capacitor, C705. The resultant d.c.
voltage, protected by FS701 feeds the h.t. regulator
fo
r
the +210V supply.
07
30
is
the reference for this supply,
buffered by
emitter
follower, TR7 l I , and the Darlington
pair, TR7 l3. The return
of
the rectified 2
IOV
supply
is
via
the - 1
IV line to balance load currents
in
the low
voltage supplies.
The four low voltage supplies are derived from a single
25V secondary
of
transformer,
Tl
. Its
output
is
bridge
rectified
by
bridge connected diodes, D726
to
D729,
into the reservoir capacitor, C704.
The distribution with respect
to
the
0V
line
of
the
voltage across this capacitor
is
determined by the - I IV
shunt regulator and the +
11
V series regulator. The - I
IV
reference
is
provided by the zener diode,
0711
, with
temperature compensation diodes,
07
I3 and
D7
I
4, and
4.5
Section 4
th
e shu
nt
transistor, TR7 1
2,
co
nducts
to
maintain the
- I
IV
line at the correct potential.
The - 5V
li
ne
is
derived from this -
11
V line by the
zener diode,
D7
l2, with
the
compensation diode, D720,
followed
by
the
emitter
follower,
TR
709.
With
the
negative side
of
the
unstabilized supply across
C704
defined at -
11
V
by
that
stabilizer, the positive
side
is
applied
to
the
series regulator, IC702, which takes
up
all
variation in the unstabilized supply
to
define the
+11V line. This
is
a 15V regulator with 'low'. pin 3,
reurned
to
a
-4V
potential defined from the -5V
supply
by
R735 and R
734
.
The
+7
V supply
is
provided from the +
11
V supply
by
a
further 12V series regulator, IC70 I, operating with
respect
to
the -5V line.
A
ll
the above
outputs
are connected
to
the subsequent
oscilloscope circuitry
via
split pads
in
the copper track
pattern.
These are normally bridged by solder
but
can be
used
to
isolate each line
to
assist fault finding.
The grid and cathode supplies for the c.r.t. are derived
via
the voltage doubler circuit,
D7
I8,
D71
9,
C7
l l and
C7 I2, from the
950V
secondary
of
TI.
The negative side
of
the
unstabilised supply developed across
C7
l l and
C7
l2
is
held at approx. - 2
000V
with
re
spect
to
0V by
the series zener diode, D706, which
is
returned
to
the
stabilised cathode potential
of
- l850V. Subsequent
variations in the unstabilized supply are developed across
the series regulator,
TR707
,
of
the e.h.t. regulator. The
feedback path
of
this regulator uses the current from
th
e
- l
850V
line defined by the resisto
rs
R7 l5, R7l4 in
parallel with
R744
(the
FOCUS
pot.)
and R 720e.
The latter being within the e.h.t. network. This current
is
returned
to
the +7V line
via
R73 l , R725 and R726.
If the resultant potential
of
the tap point defined by
th
e
preset, R725,
is
not
at approx.
-4
.5
V, the current
in
transistor,
TR706
will change to correct the stabi
li
z
in
g
voltage across
TR707
.
TR706
and
TR70
7 are connected
in
cascode.
The heater
of
the c.r.t.
is
supplied directly from an
independent 6.3V secondary winding of
Tl
.
The
OSJ00
employs a novel modulation c
ir
cuit to
c
ontrol
the grid potential with
re
spect to
th
e cathode
potentia
l.
The
transistor pair,
TR70
3 and
TR
7
04
,
generate an e
sse
ntially constant current
fr
om the
collec
tor
of
TR
703. This generates a constant volta
ge
across R 720 and preset,
R7
l
3,
and
is
returned to
ground
via
the
output
of
the brig
ht
-up amplifier. Thus
signal variations from this amplifier which operates with
respect
to
0V
are transferred with the large negative d.c.
off
set
to th
e collec
tor
of
TR703.
to be applied to
th
e
grid
of
the c.r.t.,
via
the
emitter
follower,
TR
71
6.
In more detail, the constant current from
TR
703 is
defined by the e
mitter
resistance, RN720c and the ba
se
potential,
fr
om the divider,
RN
72
0a and R 720b.
This constant current source
is
returned
to
the - 200V
line (negative
of
D706) so
that
the collector
of
TR
703

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Circuit Description
(the c.r.t. grid) can move negative from the cathode. The
collector potential
is
protected by D70S against
excessive swing during switch-on or switch-off
conditions. While RN720d and R713 generate the
necessary large d.c. potential
to
couple the bright-up
signals to the grid, the high frequency components are
by-passed through C702.
The bright-up signal amplifier
is
fanned
by
the cascade
transistor pair, TR701 and
TR702
, with shunt feedback
via
R704. It responds
to
the sum
of
three inputs. The
first
is
a d.c. bias
via
R707 from the INTENSITY
control, R74S. The second
is
the external Z Modulation
signal from SKG, via R703. The third
is
the composite
signal from the collector
of
TRS07 (Fig. S see section
4.S), which provides bright-up during each timebase
sweep with blanking
of
each chop transistion
if
approp-
4.6
Section 4
riate. Diodes, D701 and D702, provide protection
against excessive external inputs and with R702, prevent
saturation
of
TR702.
The focus electrode
of
the c.r.t.
is
supplied from the
focus control potentiometer, R744, with a portion
of
the -
18SOV
supply. The astig. electrode
is
supplied
from preset, R708 driven from the
+21
0V supply
via
the
divider network R746, R747.
Minor angular misalignment
of
the gun assembly
of
the
c.r.t. or the effects
of
externally applied magnetic fields,
axial
to
the c.r.t. can be corrected by the trace rotation
coil. This coil
is
round the neck
of
the c.r.t. and the
current
is
detennined by the TRACE ROT
A
TION
control, R737, connected between the
±11
V supplies
and driving emitter followers,
TR714
and TR7
l
S.

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Maintenance
CRT CLAMP
LOCKING
RING
TRACE
ROTATION
COIL
CORRECTIONS
TRACE
COIL
L1
Fig. 2
Internal
Assembly
-
top
view
CRT
CLAMP
RETAINING
SCREW
R307
CH1
BAL
5.1
R302
CH1
GAIN
R35?
CH
2
BAL
Section 5
R725
SET
EHT
F
701
HT
FUSE
R
713
SET
INTENSITY
C405
Y
AMP
COMPENSATION
R
553
X
AMP
x
10
GAIN
R551
X
AMP
x 1
GAIN
C402 Y
AMP
COMPENSATION
R415
Y
GAIN
R506
SET
mS
TIMEBASE
RANGES
R
352
CH2
GAIN

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Maintenance
5.1 GENERAL
Figs. 2 and 3 show the internal location of the major
components, sub-assemblies and preset controls.
No regular maintenance
is required apart from routine
recalibration. The construction of the instrument is such
that full acce ss to all calibration controls and to most
c omponents can be obtained once the two halves of the
case have been removed. (See section 5.
2)
Supply voltage adjustment is made by the two selec tor
switches on the rear panel. The supply fuse is mounted
adjacent to these switches and th e supply c onnector.
This connector should be removed or the instrument
switched off before operating the switches. For I 00 or
12 0V operation a 500mA , 2 0mm slo-blo fuse is required
(Part No. 33685) , for 200 or 220V operation a 2 50mA,
20mm slo-blo fuse is required (Part No. 33684). The
internal H.T. fuse is a lO0mA, 20mm fuse (Part No.
32958) .
5.2 REMOVAL OF THE CASE
AND
SUB -ASSEMBLI ES
WARNING
DANGEROUS VOLTAGES ARE EXPOSED ONCE
THE CASE
IS REMOVED. MAINTENANCE SHOULD
BE CARRIED OUT ONLY
BY QUALIFIED PERSON-
NEL. PARTICULAR CARE SHOULD BE TAKEN ON
THE TUBE BASE AND
THE E.H.T. AREA OF THE
MAIN PRINTED BOARD WHERE VOLTAGES IN
EXCESS OF 2000V ARE PRESENT. THESE
VOLTAGES MAY BE RETAINED AS STORED
CHARGE FOR UP TO ONE MINUTE AFTER THE
SUPPLY IS DISCONNECTED.
(a)To remove the Case (Top se c tion)
DISCONNECT FROM THE SUPPLY.
Remove the two fixing screws at the top front sides
and lift the
top cover up and forward to clear the
front moulded frame and the rear plastic moulded
cover.
(b) To remove the Case (Lower section) and Handle
assembly
DISCO NECT FROM
THE SUPPLY.
Remove the two fixing screws at the
top front sides
and proceed
to remove the top cover as detailed in
(a) above. Rest the instrument upside
down and
remove the screw from the centre of the front frame,
securing
the cover. Lift the lower cover up and
forward
to clear the front moulded frame and the
rear plastic cover. It may assist this operation if the
screws holding the rear moulding are slackened
but
not removed.
(c) Removal
of the C.R.T.
Remove the case as described
in (a) and (b) above.
Disconnect the trace
rotation coil leads from pins 734
and 735 on the main printed circuit board. Unplug
the tube base assembly. The base itself
is carried on a
sm a ll printed board which has been designed to allow
5 1
Section 5
access on two edges to facilitate withdrawal from the
c.r.t. pins. Remove the single clamp fixing screw
(see Fig. 2) and
rotate the two clamp sections approx
30 ° to free the clip from the centre panel. Once the
tube and clamp assembly are free the clamp itself can
be slackened on the tube . Slide the tube backward
through the center panel until the c.r.t. face plate is
clear of the front mounting clip. The tube can then
be lifted up and drawn forward, to clear the top edge
of the front panel and frame moulding of the instru-
ment. Withdraw the tube from the shield and the two
part clamp.
When fitting a new tube operate in the rever
se order
to the above instructions, with the exception of the
tube clamp and center panel fixing screw. On re -
assembly the fixed part (rear) of the c.r.t. clamp is
located in the slotted locating holes in the bulkhead
and the retaining screw is fitted. The tube is then held
forward against the graticule in the front moulding
while
the clamping ring is rotated to hole and lock
the
tube in place. Do not over tighten this ring.
Check
the polarity of re-connection of trace rotation
coil leads. Clockwise
rotation of the front panel preset
control should cause a corresponding movement of
the trace.
(d) Removal of the Attenuator assembly
Should it be necessary during repair
to remo ve the
attenuator and screens around the pre-amplifier for
access
to components on that board or on the front
of the main board, proceed as follows.
Remove the collet fitted knob
on the timebase
switch. Access
to the collet securing screw or nut is
by prising off the clip in the centre cap on the knob.
Remove the small push
on knobs on the two Variable
Sensitivity c ontrols , the Mode switch, the Trigger
Level, the Variable Sweep and X Shift controls.
Unsolder and, using a desoldering tool clear the solder
from the three screens where they are earthed
onto
the pre-amplifier board. Unsolder and remove the
wires from
the CAL IV pin and the EXT trigger
connection on the input printed circuit board.
Unsolder also the
two signal connections to pins 20 I
and 23 I
on the pre-amplifier board.
The sub section front panel, carrying with it the two
attenuator volts /c m switches, the two AC /GND/ DC
switches and the input coupling printed board can
now be un-latched by springing
the four latch fingers
away from
the moulded frame and withdrawing the
complete unit.
Re-assembly
is the reverse of the aforementioned .
Since the two attenuator switch wafers are symmet-
rical
the shaft can be inserted in either of the two
possible alignment positions.
(e) Removal of the Input Coupling Switch printed
circuit assembly
If it is necessary to gain acce ss to the small printed

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Maintenance
C102
CH1
C
101
CH1
ATTEN INPUT ATTEN
COMP
V1
FOCUS CONTROL
R744
CONTROL POTS
PC
ASSY
R745,
S1
INTENSITY CONTROL
&
SUPPLY
SWITCH
CAPACITY
CRT BASE
__.,-
,,
-
PC ASSY
,SJ
S~
I
SUPPLY
RANGE
SELECTOR SWITCHES
Fig. 3 Internal Assemb
ly
-
botto
m
vi
ew
SKG
Z
MOD
1/P
SKH
GND
5
.3
SKD
RAMP
0/P
Section 5
C101
CH2
ATTEN COMP
TRIMMER
ADJ.
HOLES
ATTEN SCREEN
RETAINING JOINTS
Tl
POWER
TRANSFORMER
F1
SUPPLY
FUSE
PLM SUPPLY INPUT

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Maintenance
board which carried the
input
selection switches and
the
A.C
. coupling capacitors for each Y channel,
together with
the
input
network
for the External
trigger signal proceed as follows. Using a desoldering
tool
, unsolder the tags
of
the
input
screen, clear the
holes
of
solder and remove the screen. Unsolder and
remove
the
two
wires connecting the
input
printed
board with the
two
attenuator
wafer sections
of
each
volts/cm switch. Desolder the three
input
B.N.C.
sockets from this board and the three screen grounding
points. The board should then be free for removal
by
easing upward,
off
the screen tags, then rotated
to
enable the switch sliders
to
clear the front moulding,
and
so
withdrawn.
Re-assembly
is
the reverse
of
this sequence.
(f)
Removal
of
the C.R.T . Control
Potentiometer
board
If
it
is
necessary
to
gain access
to
the
control
pots.
proceed
as
follows. Remove the push
on
knobs
on
the
Focus and the Intensity controls. Ease the spacer
retaining ears
out
of
the printed board, so freeing the
board from its retaining plastic spacer. Separate the
two
control pot shafts from the moulded shaft
couplers. Full access
to
both
the
component
side and
the track side
of
the
board
is
now facilitated and the
faulty
component
can be readily accessed.
5.3 FA
ULT
FINDING
Before any fault location
is
attempted
, it
is
suggested
that all supply voltages are checked. Subsequent signal
voltages and waveforms should then be checked
according
to
the following list, which may be used
as
a
general guide and aid
to
servicing. Note
that
the typical
voltages for un-stabilized supplies are
quoted
for nominal
mid-range supply voltages.
If
a fault cannot be cleared it
is
recommended that the
instrument
is
returned
to
the manufacturer for repair
(see section
7)
.
When faults have been cleared it
is
re
c
ommended
that
the setting-up procedure
of
section
5
.4
is
followed .
For checking the supply lines there
is
a double row
of
test pins, separated by bridged split pads. These pins will
give
outputs
of+!
IV
, -
I IV, +2 10V,
+7Vand
--
SY and
if
required the currents drawn by each line can quickly
be measured simply by breaking the solder shorting the
split pad for normal working operation, and inserting a
current measuring
meter
between the
two
pins.
In
all
five cases the line feed
is
nearer
to
the rear
of
the instru-
ment, while the line load
is
c
onnected
to
the
fo
rward
pin.
Normal Operating Conditions
Unless otherwise specified the controls are set for single
channel operation with the trace centered and timebase
running. Potentials are specified with respect
to
ground
and should be measured with a high impedance volt-
meter, digital voltmeter or oscilloscope as appropriate.
5.4
a) Supplies
Unregulated
Section 5
30V
d.c. across C704 from
25V
r.m.s. secondary
voltage.
268V
d.c. across C705 from
210V
r.m.s. secondary
voltage
2.SkV d.c. across
C71
I+
C712 from
950V
r.m.s.
secondary voltage.
Stabilized
+210V
+!IV
+7V
-SV
- I
IV
±
21V
±0.SV
+o.4V,
-0.6V
-10.
4V
,
-0.6V
±0.SV
Note: EHT regulator should be set for collector
of
TR707
to
be at +405V for nominal supply voltage.
b)
Y
Amplifier
Test Point D.
C.
Level Sensitivity
TR203/204
Collector +7V
IC301, pin I
+IV
±0.
8V
IC301, pin 14
IC301, pins 7, 8
+IV
±0.8V
+3
.SV
TR401/402
Collector
TR403/404
Collector
TR405/406
Collector
TR4057
/
408
Base
TR407
/408
Collector
c) Ramp Generator
Test Point
+3
.
7V
+7
.7V
+12.6V
+15 .6V
+I
ISV
Signal
2mV/cm
65mV/cm
each side
40mV/cm
each side
140mV/cm each side
6.8V/cm each side
Across R265
or
R266 0.8V d.c. at "cal"
0.3V d.c. at min.
1('261 pin 3 and pin 6
+3
.7V ramp from
0.IV
level
TR
2
64
Collector
d)
X
Amplifier
Test Point
TRS
12
Collector
TRS
11
Emitter
TRS 14 Base
TRS 13/5I3
+3.7V ramp from base level
between 0 and +4V dependent
on sweep rate selected.
D.C. level
+0.
65V
(Centre Screen)
+3
.7V
(Centre Screen)
- 3.
0V
+I 18V
Signal
S00mV/cm
6.
0V
ramp
S00mV/cm
6.
0V
ramp
12V
/cm
each side
140V ramp each side