Telequipment Serviscope S51A User manual

©)
SERVISCOPE
TYPE
$51
-
All
Telequipment
instruments
are
the
subject
of
continuous
development
and
improvement
and,
_in_
consequence,
may
incorporate
minor
detail
changes
from
the
information
contained
herein.
"Serviscope'
and
'TelequipmenT''
are
registered
trade
marks
of
TELEQUIPMENT
LIMITED
313
Chase
Road
London,
N.14.
Copyright
JUNE
1966

OPERATING
INSTRUCTIONS
SERVISCOPE
TYPE
551
CONTENTS
GENERAL
DESCRIPTION
S51A
/
S51E
/
S51T
FIRST
TIME
OPERATION
Use
of
Controls
Simplified Method
CIRCUIT
DESCRIPTION
eee
MAINTENANCE
AND
ADJUSTMENT
PROCEDURES
COMPONENTS
LIST
vee
soe
CIRCUIT
DIAGRAMS
see
COMPONENT
LOCATION
PLATES
FRONT
PANEL,
CONTROLS
PRINTED
CIRCUIT
LAYOUT
18
25
28/29

GENERAL DESCRIPTION
The
S51
Serviscope
is
produced
in
three
versions:
S
51A
~
general
purpose
Oscilloscope.
S
51E
-
simplified
educational
version
with
the
NORMAL/TV
FIELD
switch
and
INT/EXT
switch
both
deleted,
and
the
time
base
always
triggered
by
an
internal
signal.
Also
inthe
S51E
the
sawtooth
voltage
is
brought
out
to
a
terminal
on
the
front
panel
marked
SWEEP
OUTPUT,
at
an
amplitude
of
approxi-
‘mately
20
v
Pto
P.
(The
SWEEP
OUTPUT
terminal
re-
places
the
EXT
TRIG
terminal
on
the
S
514A.)
S
51T
~-
similar
to
the S
51A
but
incorporates
an
additional
Horizont-
al
Pre-Amplifier,
with
a
gain
of
X10.
A
switch
at
the
rear
of
the
instrument
enables
the
Pre-Amplifier
to
be
switched
out,
when
the
S
51T
has
a
performance
and
specification
identical
to
the
S
51A.
With
the
Pre-Amplifier
switched
in,
the
X
Amplifier
gain
is
increased
to
100
mV/cm
and
the
bandwidth
is
DC
to
approximately
10
Kc/s
at
-3dB.
CATHODE RAY TUBE
The
5'!
flat
faced
tube
operates
at
3
Kv
overall,
giving
an
extremely
bright
fine
trace
over
the
whole
of
the
working
area
(8
cms.
x
8cms.).
A
Pl
phosphor
is
normally
supplied
but
a
long
persistence
tube
is
available
if
specified.
A
green
filter
improves
the
contrast
under
conditions
of
high
ambient
light.
VERTICAL
DEFLECTION
AMPLIFIER
The
amplifier
consists
of
two
stages.
A
cathode
coupled
input
stage,
the
output
of
which
drives
a
cathode
follower,
and
an
output
stage
consisting
of
a
long
tailed
pair,
the
signal
being
fed
to
one
grid
and
a
DC
shift
voltage
to
the
other
grid.

The
amplifier
has
a
sensitivity
of
100mV/cm
and
a
bandwidth
of
DC
to
3
Mc/s
(-3dB.
approx.).
The
nine-position
input
attenuator
is
frequency
compensated
and
gives
sensitivities
cf
100mV,
200mV, 500mV,
1V,
2V,
5V,
10V,
20V,
50V,
per
cm.
The
input
impedance
is
1
megohm,
shunted
by
about
30
pf.
SWEEP CIRCUIT
The
sweep
generator
consists
of
a
Miller
run-down
circuit.
Six
preset
sweep
speeds
are
provided
from
1
usec/cm.
to
100Msec/
cm.
A
variable
control
with
a
10:1
range
provides
overlap
between
fixed
ranges
and
reduces
the
slowest
sweep
to
l
sec/cm.
HORIZONTAL
AMPLIFIER
The
X
GAIN
control
expands
the
trace
to
approximately
2
times
and
sufficient
shift
is
provided
to
enable
any
part
of
the
expanded
trace
to
be
positioned
centrally
on
the
screen.
TRACE UNBLANKING
D.C.
coupling
of
the
unblanking
waveform
gives
uniform
trace
brightness
at
all
sweep
speeds
and
operates
in
such
a
way
that
the
time
base
flyback
is
completely
eliminated.
TRIGGERING
Two
modes
of
triggering
are
provided.
1.
AUTO.
On
this
setting
the
sweep
free
runs
at
a
slow
speed
in
the
absence
of
an
input
signal,
but
will
be
triggered
automatically
as
soon
as
an
input
signal
is
applied.
This
mode
of
operation
can
be
used
for
90%
of
all
normal
laboratory
uses.

2.
TRIGGER
LEVEL
SELECTION.
With
the
AUTO
switch
OFF
the
Trigger
Level
Control
allows
the
sweep
to
be
triggered
at
any
point
on
the
input
waveform.
The
circuit
will
trigger
internally
on
2mm.
of
displayed
signal,
and
externally
(except
$51
E)
from
3v.
peak
to
peak.
T.V. SYNC
The
built-in
TV
sync
integrator
circuit
(S51A
and
S51T
only)
makes
it
possible
to
trigger
the
sweep
from
the
Frame
pulses
of
a
composite
Television
waveform.
REAR
CONNECTORS
Connectors
on
the
rear
panel
provide
access
to
the
Horizon-
tal
Amplifier
and
intensity
modulation
of
the
beam.
COOLING
The
S51
is
cooled
by
convection.
Air
enters
the
bottom
of
the
case
and
is
drawn
up
past
the
tubes
and
cther
hot
components,
passing
out
through
the
slots
at
the
top.
Do
not
obstruct
the
air
flow
in
any
way.
Do
not
put
anything
on
top
of
the
instrument
and
make
sure
that
there
is
an
air
Space
underneath.

STARILITY
TV FELD
EXT. TRIG
aot

FIRST TIME OPERATION
CHECK SUPPLY VOLTAGE
To
check
that
the
oscilloscope
is
adjusted
to
the
correct
supply
voltage
remove
the
cover
by
undoing
the
two
screws
at
the
rear
of
the
instrument.
The
correct
setting
will
be
obtained
by
soldering
the
required
links
for
110
volt
or
220'volt
operation
and
taking
the
supply
leads
to
the
appropriate
tags
as
shown
below.
Set for 220 volts Set for 110 volts
~~
Operation
Operation
0 0
Link
o- o——
Mains input Link Mains input
110 —— 110 ————
Link
110 110 ——~
+10 +10
+20
+20
USE OF CONTROLS
Unless you are familiar with this type of oscilloscope, follow
these
simple
instructions
carefully
and
then
run
through
the
proced-
ure
a
few
times
to
feel
thoroughly
at
home
with
the
instrument
before
putting
it
into
use.
,
Set the front panel controls as follows:
INPUT SWITCH D.C.
VOLTS/CM .5
FOCUS Mid position

Y
SHIFT
Mid
position
BRILLIANCE
Fully
anti-clockwise
X
GAIN
Fully
anti-clockwise
X
SHIFT
Mid
position
STABILITY
Fully
clockwise
TRIGGER
LEVEL
Anti-clockwise
to
position
just
before
switch
operates
TIME/CM
1
ms
TRIG.
SELECTOR
Normal.
+ve
Int.
Switch
on
and
allow
a
few
minutes
for the
instrument
to
warm
up.
Now
advance
the
brilliance
control
until
a
trace
appears
and
position
the
trace
in
the
centre
of
the
screen
by
means
of
the
X
and
Y
SHIFT
control.
Adjust
the
FOCUS
control
for
a
clean
sharp
trace.
Now
back
off
the
STABILITY
control
until
the
sweep
just
fails
to
free
run.
This
is
the
normal
position
of
the
STABILITY
control
and
once
it
is
set
it
should
not
require
any
re-adjustment
except
at
the
very
highest
sweep
speeds.
The
instrument
is
now
ready
for
use.
You
will find
that
if
the
TRIGGER
LEVEL
control
is
turned
fully
anti-clockwise
to
operate
the
AUTO
switch,
the
trace
will
re-
appear.
In
this
condition
the
instrument
is
ready
to
accept
almost
any
input
waveform
and
trigger
automatically
from
it,
the
only
ad-
justments
required
are
the
selection
of
the
appropriate
sweep
speed
and
Y
Sensitivity
(VOLTS/CM).
However,
in
order
to
use
the
S51
_
to
best
advantage
the
functions
of
the
controls
should
be
understood
fully
and
the
following
procedure
will
demonstrate
their
use.
Return
the
TRIG.
LEVEL
control
to
the
position
just
before
the
Switch
operates.
There
should
now
be
no
trace
visible
on
the
screen.
Connect
a
50
C/S
signal
to
the
INPUT
sockets
and
rotate
the
TRIG.
LEVEL
control
clockwise
until
the
trace
appears.
(If
the
sweep
does
not
trigger
it
is
because
the
STABILITY
control
has
been
backed
off
too
far.)
The
Scope
is
now
displaying
the
voltage
waveform.
You
will
find
that
this
is
a
very
convenient
waveform
for
demonstrating
the
functions
of
the
controls.

AUTO
On
this
setting
no
control
over
the
trigger
level
is
available.
The
sweep
automatically
adjusts
itself
to
trigger
at
approximately
the
mean
level
of
the
input
waveform.
You
can
use
this
setting
for
practically
ail
applications
involving
repetitive
waveforms
of
a
fairly
simple
nature
and
the
sweep
generator
will
trigger
automatically
on
signals
between
about
50
c/s
and
1
Mc/s.
provided
the
amplitude
exceeds
about
2
mm..
In
the
AUTO
position
with
no
input
signal
the
trace
will
be-
come
progressively
less
bright
as
the
sweep
speed
is
increased.
This
is
normal
since
in
the
absence
of
a
trigger
signal
the
sweep
free
runs
at
about
50
c/s
whatever
the
setting
of
the
speed
control.
As
soon
as
an
input
signal
is
applied
the
sweep
will
immediately
synchronise
to
it
and
the
trace
will
revert
to
its
full
brightness.
TRIG SELECTOR
There
are
four
positions
on
the
selector
switches.
For
most
purposes
use
the
positive
or
negative
normal
positions
depending
on
the
polarity
of
the
input
waveform.
The
other
position
brings
the
internal
integrating
circuit
into
use
on
TV
waveforms
enabling
the
sweep
to
be
triggered
from
the
Frame
pulses
(the
+ve
TV
positions
refer
to
positive-going
video
signals,
i.e.,
picture
+
ve,
sync.
-
ve).
When
triggering
from
a
TV
frame
pulse,
adjustment
of
the
TRIG.
LEVEL
control
will
deter-
mine
which
of
the
broad
pulses
actually
triggers
the
sweep.
The
integrating
circuit
for
the
frame
pulse
can
be
useful
on
occasions
for
frequency
discrimination.
For
instance,
an
audio
signal
containing
a
large
proportion
of
HF
noise
will
trigger
better
‘on
the
TV
frame
position,
the
integrator
acting
as
a
low
pass
filter.
For
triggering
from
an
external
signal
select
the
EXT
setting
and
connect
the
signal
into
the
external
trigger
socket.

X-GAIN and X-SHIFT
With the X-GAIN control in the minimum (anti-clockwise)
position,
the
trace
will
be
approximately
8
cm.
long
and
the
X-SHIFT
control
should
be
used
to
centre
this
trace about
the
10
x
8
cm.
ruled
graticule.
Increasing
the
X-GAIN
control
expands
the
trace about
the
centre
of
the
screen
up
to
a
maximum
of
X2
and
the
X-SHIFT
control
is
then
used
to
position
the
required
portion
of
this
trace on the screen.
It should be noted that the time calibration only holds good at
the
minimum
setting
of
the
X-GAIN
control.
If
you
wanttomeasure
time intervals at any other setting the speed must be standardised at
this setting.
VOLTS PER CM.
This is a nine-position switch which inserts a series of fre-
quency
compensated
resistance
dividers
between
the
input
socket
and the Vertical Amplifier. Normally this is used merely to obtain
a picture of convenient height, but if the gain of the Amplifier is
standardised, direct readings of the input voltage can be made.
D.C./A.C. SWITCH
On the A.C. position this switch inserts a blocking capacitor
in series with the input of the Vertical Amplifier removing the D.C.
component of the signal. This is the condition in which the $51 will
normally
be
used
unless
it
is
specifically
required
to
include
the
D.C.
component
or
to
use
the
instrument
on
very
low
frequency
sig-
nals.
The
time
constant
of
the
input
circuit
on
the
A.C.
position
is
such that the response is 3 dB down at 2 cycles, which, while
adequate for all normal purposes, may limit the application in some
instances.
For
example,
you
will
notice
that
on
a
50
cycle
square-
Wave
a
pronounced
tilt
occurs
on
the
A.C.
position.
If
a
longer
time constant is required, a higher capacity external blocking capa-
citor must be used with the input switch set to D.C.

REAR CONNECTORS
1. X-Amp Input. This socket provides an access to the input of
the Horizontal Deflection Amplifier and is suitable for signals
between about 4 and 10 volts p.p. The X-GAIN control gives about
a 2 to 1 variation of gain. When using the X-Amplifier the sweep
can be stopped by turning the VARIABLE SPEED control fully anti-
clockwise. The input impedance is about 500 K and the input capa-
city about 100 pf. The frequency response is 3 dB down at 5 cycles
and at about 200 Kc/s.
-2s—-Z.-Mod. This socket is connected via a blocking capacitor
to the cathode of the CRT. Thus, a negative pulse will brighten the
trace. The time constant of this circuit is .01 mf and 10, 000ohms.
SIMPLIFIED METHOD
In the above instructions the functions of controls have been
explained in some detail so that the engineer using the S51 may fully
appreciate its capacities and the method of function. There will,
however, be a large number of users who will not require all the
facilities provided and to whom simplicity of operation is of major
importance. The following simplified instructions will suffice for
most applications, in fact for any application where the older type of
Oscilloscope could be used the following method will provide better
results much more quickly and simply.
Set input switch to A.C.
Switch on and allow a few minutes to warm up.
Turn STABILITY control fully clockwise and adjust
BRILLIANCE and FOCUS controls for a sharp trace.
Back off STABILITY control until the TIME BASE stops. The
STABILITY control once set should not require any further adjust-
ment.
The instrument is now set for use.

For
most
applications
switch
to
AUTO,
connect
input
signai,
and
adjust
VOLTS/CM
switch
to
give
a
convenient
size
trace.
Use
TIME/CM
and
VARIABLE
as
coarse
and
fine
frequency
controls
to
suit
the
input
signal.
For
T.V.
waveforms
use
T.V.
FIELD
position
(S51A
and
S51T
only).
If
the
sweep
fails
to
lock,
the
STABILITY
control
has
been
turned
up
too
far.
For
some
input
waveforms
and
sometimes
for
T.V.
wave-
forms
it
may
be
necessary
to
adjust
the
TRIG.
LEVEL
control
rather
than
to
use
the
AUTO
position.
10.

For
most
applications
switch
to
AUTO,
connect
input
signai,
and
adjust
VOLTS/CM
switch
to
give
a
convenient
size
trace.
Use
TIME/CM
and
VARIABLE
as
coarse
and
fine
frequency
controls
to
suit the input signal.
For
T.V.
waveforms
use
T.V.
FIELD
position
(S51A
and
S51T
only).
If
the
sweep
fails
to
lock,
the
STABILITY
control
has
been turned up too far.
For
some
input
waveforms
and
sometimes
for
T.V.
wave-
forms
it
may
be
necessary
to
adjust
the
TRIG.
LEVEL
control
rather than to use the AUTO position.
10.

CIRCUIT DESCRIPTION
VERTICAL AMPLIFIER
The vertical amplifier consists of three double triodes.
V1A and V1B form a cathode coupled amplifier pee with RV}!
acting as the gain control.
The signal is taken from V1B anode and drives the output
stage V3 via cathode follower V2A.
V3 consists of a tas -tailed pair with the signal taken to
V3A and the vertica ift applied to V3B.
V2B acts as a low impedance HT supply for Vl.
The signal at the anode of V3B is taken to the INT/EXT.
trigger switch.
The HT supply for the trigger circuit, V4 and V5 is taken
from a common resistor R19 in the cathode circuit of V3.
TRIGGER CIRCUIT
The trigger selection is performed by three switches; SW2
selects the INT/EXT. triggering signal and connects it to the grid
of phase splitter V4B. SW3 selects the positive or negative output
of the phase splitter and connects it to SW4 which either passes the
signal direct to V4A or via an integrating circuit. This position,
marked TV field, integrates the field pulses of a television wave-
form and attenuates the line pulses allowing the time base to be
triggered by the field sync. pulses.
From SW4 the signal is fed to V4A and V5B which form a
cathode coupled bistable switch, the switching level being adjusted
by the grid potential of V4A. Onthe AUTO position the switchSW5
is opened and the grid of V4A is returned to the grid of V5B. In the
absence of a signal V4A, V5B oscillates at a frequency determined
ll.

by the time constant R38, C18 but as soon as any input signal
between about 50 c/s and 1 Mc/s is applied to the grid of V4A, the
self oscillation ceases and the multivibrator synchronises to the
signal frequency. The square wave appearing at the anode of V5B
is differentiated, the positive pulse removed by MR5 and the nega-
tive pulse used to trigger the time base.
TIME BASE & HORIZONTAL AMPLIFIER
V6A is the Miller sweep generator, the speed of run down
being controlled by SW7A and the VARIABLE SPEED control.
The Miller valve is keyed by V5A and V6B which together
form aD.C. coupled multivibrator.
In
the
rest
position
of
the
timebase,
V5A
is
off
and
its
anode
potential
is
clamped
by
MR6.
V6B
is
conducting.
A
negative
trigger
pulse
from
V5B
lowers
the
grid
of
V6B
and
hence
the
anode
of
V6A.
This
is
coupled
to
the
grid
of
V6A,
so
reducing
the
valve
current.
The
resulting
rise
in
screen
potential
developed
across
R69
is
coupled
via
R71
and
SW7A
tothe
grid
of
V5A.
This
causes
V5A
anode
voltage
to
fall,
which
leads
to
regenerative
action
where-
by
V6B
becomes
quickly
cut
off
and
V5A
is
hard
on.
When the run down has reached the point where the cathode
of V6B has fallen to near the grid voltage of V6B then V6B starts to
conduct and a negative pulse is applied to the grid of V5A. Regen-
eration again takes place driving V5A to cut off and V6B to
conduction.
The positive going voltage at V6B anode, developed during
the sweep, is coupled to the modulator plate of the CRT, to provide
trace brightening. ~
The STABILITY control RV11 sets the grid potential of V5A
to the point just short of the free running condition.
The linear sweep voltage at the anode of V6A is taken via
R57, C23, RV15, to the grid of the horizontal amplifier V7.
Horizontal shift voltage is applied to the grid of V7A and the outputs
at the anodes of V7A and B drive the C.R.T. X plates.
12.

Transistor TRI! in the common cathode circuit, acts as a
constant current source and provides a baianced output at the two
anodes.
An external signal can be applied to the grid of V7B through
a connector at the rear of the instrument. In this condition the
time base should be switched off with the VARIABLE SPEED
‘control.
POWER SUPPLY
Silicon rectifiers MR1 and MR2 in a voltage doubling circuit
supply the various HT voltages via smoothing resistors R12 and
- R22.
The negative high voltage supply for the C.R.T. is derived
from the secondary of the power transformer via MR4. MR4
also supplies the negative supply to the STABILITY control.
The positive high voltage supply is derived from MR3, the
negative side of the reservoir condenser C10 being returned to the
HT +ve supply.
C.R.T.
Intensity modulation signals can be supplied tc the cathode
-of the C.R.T. via C9, via a terminal on the rear of the instrument.
Approximately 15 volts, negative going signals are
required.
RV7 provides preset adjustment for ASTIG setting and RV6
. BLKG allows the stationary bright spot to be adjusted to a maxi-
mum by varying the Al potential.
13.

MAINTENANCE ADJUSTMENTS
The
simplicity
of
the
circuitry
of
the
$51
makes
it
an
extremely
reliable
instrument,
and
for
the
most
part
servicing
will
be
limited
to
the
replacement
of
defective
tubes.
Replacement
of
_tubes
in
the
vertical
Amplifier
will
have
very
little
effect
on
its
per-
formance
and
no
re-adjustment
should
be
necessary.
In
the
sweep
generator
and
Horizontal
Amplifier
the
tubes
are
not
particularly
critical
and
you
will
find
that
you
can
replace
these
without
having
to
alter
the
internal
adjustments.
If
for
any
reason
the
internal
pre-
set
controls
do
require
adjustment,
the
following
detailed
instruc-
tions
will
allow
you
to
do
this
quickly
and
accurately.
INPUT ATTENUATOR
In
order
to
adjust
the
input
attenuator
compensation
you
will
need
a
squarewave
generator
with
a
frequency
of
approximately
2
Kc/s
and
whose
output
can
be
varied
between
.2
volts
and
100
volts.
~The
rise
time
of
the
squarewave
need
not
be
particularly
fast
but
it
must
have
a
good
flat
top
and
bottom.
Connect
the
squarewave
gen-
erator
to
the
input
socket
and
adjust
the
output
to
approximately
.2
volt.
Set
the
input
attenuator
to
:1
volt
per
cm.
and
adjust
the
sweep
controls
so
that
you
are
displaying
3
cycles
of
the
square-
wave.
Now
carry
out
the
following
procedure
step
by
step,
adjust-
ing
each
trimmer
to
give
a
square
corner
to
the
squarewave.
On
each
setting
of
the
input
attenuator
you
shouid
adjust
the
output
of
the
squarewave
generator
to
give
a
trace
of
approximately
2-3
cm.
amplitude.
Set Input Attenuator to: Adjust
22 volts per cm. Cl1l2
i mous C113
"! tt Wt C104
! tt W C108
C109
" moo" C105
OWN 1
If
you
have
carried
out
these
adjustments
correctly
the
20
volts
per
cm.
and
the
50
volts
per
cm.
ranges
are
automatically
correct.

In
order
to
adjust
the
capacitors
C102
and
C103
it
is
necessary
to
use
the
high
impedance
probe
as
these
two
capacitors
only
affect
compensation
when
this
probe
is
inuse.
Remove
the
squarewave
generator
from
the
input
socket
and
plug
in
the
high
impedance
probe,
connect
the
output
of
the
squarewave
generator
to
the
probe
tip
and
set the
input
attenuator
to
.1
volt
per
cm.,
set
the
output
of
the
sSquarewave
generator
to
give
approximately
2
cm.
amplitude
and
ad-
just
the
probe
trimmer
(this
is
accessible
through
the
hole
in
the
probe
body)
to
give
a
flat
top
to
the
squarewave,
now
switch
the
input
attenuator
to
the
1
volt
per
cm.
range,
re-adjust
the
output
of
the
squarewave
generator
and
adjust
C2,
set
the
input
attenuator
to
the
10
volts
per
cm.
range
and
adjust
C3.
All
other
ranges
wili
auto-
matically
be
correct.
VERTICAL AMPLIFIER
Adjustment
of
the
high
frequency
compensation
of
the
vertical
amplifier
shouid
oniy
be
carried
out
if
you
have
at
your
disposal
a
squarewave
generator
which
is
capable
of
producing
an
accurate
Squarewave
at
a
frequency
of
about
250
Kc/s
with
a
rise
time
less
than
100
millimicroseconds
and
which
is
known
to
be
absolutely
free
from
ring
or
overshoot.
The
compensation
circuits
in
the
vertical
amplifier
are
extremely
stable
and
unless
such
a
generator
is
avail-
able
you
would
be
wise
not
to
attempt
any
readjustment..
Set
the
input
attenuator
switch
to
.1
volt
per
cm.
and
adjust
the
output
of
the
squarewave
generator
to
give
a
trace
of
approxima-
tely
2-3
cm.
amplitude
(the
output
frequency
on
the
generator
should
be
between
200
and
300
Kc/s).
The
variable
Ll
is
adjusted
to
give
a
flat
topped
squarewave
with
a
fast
rise
time,
square
corners
and
no
overshoot.
The
only
other
variable
on
the
vertical
amplifier
is
the
set
GAIN
control.
TRIGGER CIRCUIT
The
only
adjustment
necessary
in
the
TRIGGER
circuit
is
an
occasional
setting
of
the
TRIGGER
sensitivity
control
RV9;
this

should
be
set
so
that
the
TRIGGER
circuit
will
operate
when
the
trace
amplitude
on
the
screen
exceeds
2mm.
If
any
attempt
is
made
to
increase
the
sensitivity
beyond
this
point
erratic
operation
will
almost
inevitably
result.
Connect
a
signal,
say
a
2
Kels
square
wave
to
the
input.
Now
set
the
input
attenuator
to
give
a
trace
2
mm.
high
and
adjust
the
TRIGGER
sensitivity
control
so
that
_at
a
critical
setting
of
the
TRIG.
LEVEL
control
the
sweep
will
just
trigger;
now
reduce
the
trace
amplitude
to
1
mm.
and
make
sure
that
the
sweep
will
not
trigger
on
this
signal.
SWEEP
GENERATOR
&
HORIZONTAL
AMPLIFIER
To
make
a
complete
readjustment
of
the
Sweep
Generator
and
_
Horizontal
Amplifier,
carry
out
the
following
procedure:-
Remove
the
lead
to
the
Moduiator
Anode,
pin
7
on
the
CRT.
Set
the
TIME/CM
switch
to
100
usecs.
Now
advance
the
BRILLIANCE
control
until
you
can
see
the
spot
at
the
beginning
of
the
trace
and
you
will find that
by
adjusting
C23
you
will
be
able
to
make
a
small
"tail''
appear
to
one
side
of
the
spot
or
the
other.
The
correct
setting
for
C23
is
the
point
at
which
this
"tail"
just
disappears
into
the
spot.
Reconnect
the
lead
to
the
Modulator
Anode
on
the
CRT.
Now
set
the
TIME/CM
switch
to
100
usecs
and
the
VARIABLE
speed
to
the
cal.
position.
The
X-GAIN
should
be
at
minimum
and
the
trace
centred
using
the
X-SHIFT
control.
Connect
an
accurately
known
i100
usec.
pulse
repetition
frequency
(19
Kce/s)
to
the
input
terminals
and
adjust
RV15
so
that
the
TIME/CM
is
correct.
Adjustment
of
RV15
will
cause
the
trace
to
move
horizontally
so
it
should
always
be
recentred
using
the
_X-SHIFT
control.
For
greatest
accuracy,
the
calibration
of
the
TIME/CM
should
be
carried
out,
using
the
centre
4
cms.
ofhorizon-
tal
trace.
16,

CRT CIRCUIT
The
Cathode
Ray
Tube
used
in
the
S51
is
equipped
with an
inter-deflector
plate
shield.
This
is
returned
to
HTi
via
a
1
meg-
ohm
preset
RV8.
This
is
adjusted
in
order
to
ensure
that
the
inter
plate
shield
is
at
the
average
potential
of
the
deflector
plates.
Variation
of
the
inter
plate
shield
voltage
serves
to
correct
pin
cushion
and
barrel
pattern
distortion.
This
control
is
set
during
test.
No
further
adjustment
should
be
necessary
unless
the
tubeis
changed.
HIGH
IMPEDANCE
PROBE
The
adjustment
of
the
probe
compensation
is
best
carried
out
with
a
squarewave
generator
with
an
output
frequency
of
approxima-
tely
1
Kc/s.
The
compensation
trimmer
is
accessible
through
the
hole
in
the
body
of
the
probe
and you
should
adjust
this
to
give
a
Square
corner
to
the
squarewave,
17,