AVO EA 113 Operating and installation instructions
El
CTRONIC
AYOME
ER
TYPE
EA
113
SERVICING
INFORMATION
ELECTRONIC
A
YOMETER
TYPE
EA
113
These
instructions
have
been
written
to
provide
a
general
guide
to
the
servicing
of
the
Electronic
Avometer
EA
113.
No
attempt
should
be
made
to
service
this
Avometer
unless
the
full
range
of
recommended
test
equipment
as
shown on
Pages
6
and
7
is
available.
In
the
event
of
a
major
overhaul
the
instrument
should
be
returned
to
Avo
Limited
or
to
the
representative
in
your
territory.
CONTENTS
Introduction
TEST
FACILITIES
AND
~UIIMENT
~UIRED
1•
Essential
Test
Facilities,
Equipment
and
Conditions
Instruments
and
Test
Gear
Tools
and
Other
Aids
Spare
Parts
Miscellaneous
Items
PRELIMINARY
PROCEDURE
2.
3.
4.
Suggested
Repair
Procedure
Consideration
of
Customer's
Report
Rapid
Functional
Checks
REMOVAL
OF
ASSEMBLIES
5.
Replacement
of
Battery
or
Fuse
6.
Removal
of
the
Panel
from
the
Case
7. Removal
of
the
Printed
Circuit
Range Board
8.
Removal
of
the
Amplifier
Board
9.
Removal
of
the
Movement from
the
Panel
FAULT
FINDING
AND
SERVICING
INFORMATION
10.
11
•
Fault
Finding
Table
Servicing
Information
DISMANTLING
AND
REPLACEMENT
12.
13.
14.
Dismantling
the
Movement
Front
Panel
Replacement
Slide
Switch
Replacement
ELECTRICAL
TESTING
15.
16.
17.
18.
19.
20.
Transistor
Selection
Procedure
General
Functional
Check
D.C.
Calibration
Tests
and
Adjustments
A.C.
Calibration
Tests
and
Adjustments
Final
Procedure.
Plates,
Components
List
and
Circuit
Diagrams.
Page
5
6
6
7
7
7
8
8
9
10
11
11
11
12
13
14
17
19
20
21
21
21
22
23
24
SERVICING
INFORMATION
INTRODUCTION
For
almost
fifty
years
the
Avometer
has
built
for
itself
an
unrivalled
reputation
for
reliability
and
service.
It
is,
however,
inevitable
that
instruments
fail
from
time
to
time,
mainly
due
to
accidental
misuse,
and
when
they
do,
it
is
essential
that
they
are
repaired
to
the
highest
possible
standard.
This
booklet
has
been
produced
therefore
to
aid
our
customers
and
associates,
both
at
home
and
overseas,
and
it
is
hoped
that
it
will
form a
useful
guide
to
the
trained
engineer
who
has
the
task
of
servicing
our
products.
The
instrument
has
not
been
dealt
with
in
absolute
detail,
for
to
do
so,
would
be
beyond
the
scope
of
this
publication,
although
it
is
assumed
that
the
engineer
undertaking
the
work
has
a good knowledge
of
the
principles
of
moving
coil
multi-range
measuring
instruments
and
electronics.
The
instrument
has
been
'broken
down'
in
such
a manner
that
an
engineer
with
suitable
tools
and
test
gear,
can
take
Avo components
and
spare
parts
and
fit
them
into
the
instrument,
which
will
then
only
require
a minimum
degree
of
calibration
and
test.
Particular
note
should
be
taken
of
the
advice
which
is
given
regarding
the
use
of
complete
sub-assemblies.
It
is
advisable
to
keep
a number
of
key
items
in
stock,
in
order
that
they
can
be
immediately
available
when
required.
A
faulty
movement
can
be
returned
to
the
factory
and
an
allowance
will
be
made
for
serviceable
component
parts.
No
attempt
should
be
made
to
service
an
Avometer
unless
the
full
range
of
recommended
test
equipment,
is
available.
In
the
event
of
a
major
overhaul
the
instrument
should
be
returned
to
the
Avo
representative
in
your
territory.
- 5 -
TEST
FACILITIES
AND
E{lUIPMENT
&yJUIRED
1.
ESSENTIAL
TEST
FACILITIES,
E{lUllMENT
AND
CONDITIONS
Certain
facilities
and
equipment
are
absolutely
essential
before
any
consideration
can
be
given
to
the
possibility
of
undertaking
the
repair
of
the
electronic
Avometer.
To
assist
in
deciding
whether
the
facilities
and
equipment
are
adequate,
a
list
of
tools
and
test
gear
which
will
form
the
minimum
requirements
is
given
below.
If
it
is
decided
to
undertake
the
more
complicated
tasks
then
very
much more
equipment
will
be
required.
For
certain
operations,
good
sight
and
a
steady
hand
are
essential.
The room
in
which
repairs
are
to
be
carried
out
should
preferably
have
air
filtering
and
be
temperature
controlled.
The
bench
tops
should
be
covered
with
plain
light
coloured
linoleum
or
similar
material.
Good
daylight,
but
shielded
from
direct
sunlight
is
satisfactory,
but
in
any
case
it
should
be
supplemented
for
certain
operations
by
light
from
tungsten
lamps
with
sui
table
shades.
Care
should
be takem
not
to
create
dazzle
or
excessive
lighting
contrast
and
it
is
suggested
that
when
dependent
on
artificial
lighting,
a
general
bench
illumination
of
75
lumens
per
square
foot
(ft.
candles)
is
satisfactory.
Do
not
smoke -
this
is
particularly
important
when
inflammable
or
cleaning
fluids
are
exposed.
INSTRUMENTS
AND
TEST
GEAR
Avo
Digital
System
or
Suitable
precision
voltmeters
a.c.
and
d.c.
)
Suitable
precision
ammeters
a.c.
and
d.c.
)
S
·t
bl
· ·
hmm
t )
equivalent.
u1 a e
prec1s1on
o e
ers
F.E.T.
Test
Gear No. 467
(drg.
No. A6170-018
available
to
construct)
Dual Power
Supply
+ 2.3V
to
+
3.4V.
Audio
Oscillator
with
1V
output
Electronic
Avometer
EA
113
(spare)
D.C.
Calibrator
(Bradley
123B
or
equivalent)
Controlled
Voltage
&
Current
Supplies
(Avo
Test
Console
&
Extension
Box
T670A
or
equivalent.)
A.C.
Calibrator
(Hewlett
Packard
746A
or
equivalent.)
High
Voltage
Amplifier
(Hewlett
Packard
746A
or
equivalent.)
Mallory
Duracell
ZM9
1.4V
batteries
A
substitute
movement
encased
and
with
flying
leads
Flash
testing
equipment
Microscope
with
16mm
objective
and
X10
or
X15
eyepiece
Thermometer
Draught
proof
box
with
mountings
for
movement
and
having
a
glass
cover
and
connections
for
test
purposes.
Avo
Magnetising
Unit
.•
Avo
Transistor
Test
Set
Type TT.166.
(or
equivalent)
- 6 -
TOOLS
AND
OTHER
AIDS
Movement Assembly
Jig
Avo
Part
No. AF5075
De-soldering
equipment
with
solder
removal
facilities
A
small
soldering
iron
Lightweight
soldering
iron
for
movement
repairs
Screwdrivers
for
2BA,
4BA,
and
6BA
screws
Torque
screwdriver
8BA
3
to
4
in.
lb.
A
set
of
watchmaker's
screwdrivers
A
set
of
BA
box
spanners
5/16
in.
BSF
box
spanner
A
set
of
open-ended
BA
spanners
Tweezers
suitable
for
light
work on moving
coil
hairsprings,
etc.
Pliers,
various
sizes
A
pair
of
circlip
pliers
A
pair
of
side
cutters
A hand
drill
A
set
of
twist
drills
from t
in.
diameter
(6mm)
approximately
downwards
One
each
of
the
following
taps:
2BA,
4BA,
6BA,
8BA
and
tap
wrench
A
pin
or
tack
hammer
Pencil
brushes
t
in.
brushes
An
eye
glass
Bellows
or
air
blast
SPARE
PARTS
A
stock
of
Electronic
Avometer
Spares
A
stock
of
recently
manufactured
appropriate
cells
A
stock
of
appropriate
electronic
components
MISCELLA.NEDUS
ITEMS
Some
small
receptacles
to
hold
piece
parts
Small
glass
jars
with
lids
for
fluids
containing
methylated
spirit,
switch
cleaning
fluids
such
as
Carbon
Tetrachloride
or
Electrolube
and
degreasers
such
as
Trichlorethylene
or
Genklene
A
reel
of
good
quality
cored
solder
(6o%
tin,
4o%
lead)
in
16
s.w.g.
or
1.5mm
such
as
'Ersin
Multicore'
A
reel
of
good
quality
solid
solder
wire
(6o%
tin,
4o%
lead)
in
20
s.w.g.
or
1mm
for
soldering
hairsprings
Tinned
copper
wire
18
s.w.g.
and
22
s.w.g.
Sleeving
for
tinned
copper
wire
Some
small
sticks
of
orange
wood
A
bundle
of
pith
or
clean
cork
A number
of
steel
needles
A mapping
pen
and
Indian
ink
Tubes
of
adhesive
such
as
Bostik
Type 299
White
Tubes
of
Bostik
Black
or
similar
glazing
compound
Vaseline
or
similar
grease
LOCTITE
retaining
compound
(Green)
Wash
leather
Cleaning
cloths.
- 7 -
PRELlMINARY
PROCEDURE
2.
SUGGESTED
REPAIR
PROCEDURE
When
the
instrument
arrives
for
repair,
examine
it
carefully
and
note
any
signs
of
damage
which
might
have
been
caused
whilst
the
instrument
was
in
the
course
of
transit.
Apart
from
internal
inspection,
do
not
proceed
with
any
repairs
until,
(a)
the
customer's
observations
regarding
the
failure
of
the
instrument
have
been
received
and,
(b)
it
is
certain
that
the
instrument
has
not
suffered
damage
in
transit.
Severe
transit
shocks
can
sometimes damage
instruments
internally,
although
externally
they
appear
to
be
perfect.
Always
give
the
customer
full
details
of
any
suspected
transit
damage,
particularly
when
the
damage
to
the
instrument
is
more
serious
than
that
reported
by him. The
customer
may
wish
to
claim
financial
damage from
the
carrier
who
shipped
the
instrument
and
because
of
this,
the
packing
material
in
which
the
instrument
arrived
should
be
retained.
It
is
also
important
that
the
carriers
should
be
informed
of
the
damage
without
delay.
If
the
customer
has
not
advised
that
the
repair
should
be
proceeded
with
irrespective
of
your
charge,
we
strongly
advise
that
the
instrument
should
be examined
and
an
estimate
submitted
before
any
work
is
carried
out.
(Do
not
overlook
the
condition
of
the
leads,
prods,
clips
and
batteries
when
quoting).
This
procedure
and
acceptance
of
the
estimate
will
provide
a
safeguard
against
disputes
arising
over
the
charge
for
the
work,
after
the
necessary
repairs
have
been
completed.
3.
CONSIDERATION
OF
THE
CUSTOMER
1S
REPORT
Testmeters
requiring
no more
than
the
replacement
of
batteries
are
often
returned
for
repair
and
it
is
therefore
advisable
to
carry
out
a
Battery
Check
before
undertaking
any
other
tests
(see
Section
4A).
If
the
batteries
are
found
to
be
exhausted,
the
instrument
should
nevertheless
be
tested
throughout
before
being
returned
to
its
owner
to
ensure
that
there
is
no
other
failure
not
reported
by
him.
It
may
be found
that
a
fault
exists
which
bears
no
relation
to
the
complaint
received.
If
so,
the
instrument
should
be opened
(see
Section
6)
and
the
full
extent
of
the
fault
be
reported
to
the
customer
before
proceeding
with
the
repair.
Should
the
cause
of
the
reported
fault
not
be
apparent,
it
may
be
one
of
an
intermittent
nature,
and
if
it
cannot
be
located
the
fullest
information
should
be
obtained
from
the
customer,
as
to
the
symptoms
and
then
concentrate
on
the
likely
portions
of
the
circuit.
Intermittent
faults
which
can
suddenly
appear
or
vanish
and
vary
in
intensity
from
slight
to
severe
can
be
very
misleading
during
diagnosis
and
difficult
to
locate.
Intermittent
faults
can
often
be
traced
by
changing
the
instrument
operating
temperature
by
~
10°
from
ambient
temperature.
- 8 -
4.
RAPID
FUNCTIONAL
CHECK
DO
NOT
OPEN
THE
INSTRUMENT
or
adjust
the
pre-set
controls
until
the
necessity
to
do
so
has
been
clearly
established.
If
incorrect
operation
of
the
instrument
is
suspected,
thv
following
brief
checks
should
first
be made. These
checks
provide
a
simple
method
of
determining
whether
the
instrument
is
functioning
normally
and
they
can
all
be
performed
without
removing
the
instrument
from
its
case.
Select
Range------.
a and centra ·
Movement
zero adjuater
(a)
With
the
Range
switch
set
to
any
position
except
OFF
and
the
Operating
Mode
switch
set
to
the
positive
and
negative
check
battery
positions
in
turn,
check
the
state
of
the
batteries.
If
the
meter
indication
is
below
the
minimum
battery
limit
marked on
the
scaleplate,
the
batteries
should
be
replaced
before
continuing
with
any
further
tests.
(See
Section
5
for
Replacement
Instructions.)
(b)
With
the
Range
switch
set
to
OFF,
the
Operating
Mode
switch
set
to
Check
battery
positive
and
the
a.c.
push-button
depressed,
check
movement
mechanical
zero.
If
required
mechanical
zero
can
be
set
using
the
slotted
screw
adjuster
on
the
side
of
the
instrument.
(c)
Set
the
Operating
Mode
switch
to
the
left-hand
zero
position,
depress
the
d.c.
push-button
and
set
the
range
switch
to
the
.01V
position.
The
meter
should
read
zero
within
0.2,%.
(d)
Check
all
d.c.
voltage
and
current
ranges
at
f.s.d.
to
ascertain
if
they
meet
the
specified
accuracy.
(e)
With
terminals
open
circuit,
set
the
Range
switch
to
the
1M
position
and
check
that
full
scale
can
be
set
using
the
Ohm
and
Centre
Zero
potentiometer
on
the
front
panel.
The
potentiometer
should
provide
an
adjustment
either
side
of
f.s.d.
(of
about
10
or
2o%). Check
zero
ohms
by
shorting
the
terminals.
(f)
Repeat
(e)
with
the
Range
switch
set
at
positions
x100k,
x10k,
x1k
anQ.
100
positions.
- 9 -
(g)
Set
the
Range
switch
to
the
.01V
position
and
set
Operating
Mode
switch
to
the
centre
zero
position.
The
meter
should
read
approximately
half
scale.
The
centre
zero
potentiometer
should
provide
an
adjustment
of
approximately
~
10 on
the
special
centre
zero
scale.
(h)
Depress
the
a.c.
push-button
and
set
the
Operating
Mode
switch
to
the
left-
hand
zero
position.
The
meter
should
swing
to
full
scale
momentarily,
then
fall
back
towards
zero.
Set
the
Range
switch
to
the
1000V
range
and
zero
should
be
indicated
to
within+
0.~.
(j)
Check
all
a.c.
voltage
and
current
ranges
at
f.s.d.
and
note
that
they
meet
the
specified
accuracy.
(k)
Remove
all
test
instruments
and
set
the
Range
switch
to
the
OFF
position.
REMOVAL
OF
ASSEMBLIES
The
following
notes
are
given
if
the
necessity
to
open
the
instrument
has
been
established.
A
visual
examination
of
the
interior
could
show where
the
fault
lies,
particularly
if
the
fault
is
due
to
overloading
of
the
instrument.
Unless
it
is
found
to
be
essential
the
movement
should
remain
undisturbed
with
the
movement
cover
in
place.
It
must
be
emphasised
that
if
movement
servicing
is
necessary,
the
movement must
be
de-magnetised
before
any
servicing
can
be
carried
out.
Specialised
equipment
will
be
required
for
this
and
the
movement
is
such
a
specialised
item
that
in
the
event
of
defects
of
more
than
a
minor
nature,
complete
replacement
is
recommended.
5.
REPLACEMENT
OF
BATTERY
OR
FUSE
Replacement
of
the
battery
or
fuse
is
easily
effected
by
releasing
the
two
Dzus
fasteners
on
the
backplate.
Switch
first
to
the
OFF
position
and
then
remove
the
backplate
which
will
reveal
the
batteries,
the
fuse
and
a
spare
fuse.
Polarities
are
indicated
in
the
battery
compartment
and
it
is
essential
that
these
are
observed
when
replacing
the
batteries.
If
replacing
with
Mallory
Duracell
batteries
replace
the
complete
set
and
ensure
that
they
are
inserted
in
the
correct
polarity.
Under
certain
atmospheric
conditions
a
'white
frosting'
may
appear
on
these
battery
terminals.
This
is
quite
harmless,
but
should
be removed
with
a
soft
cloth
to
ensure
perfect
contact.
(This
refers
only
to
Mallory
Duracell
batteries.)
The
fuse
rating
is
3A
and
recommended
replacement
batteries
are
as
follows:
Four
Mallory
Cells
type
ZM
9
as
supplied
with
the
instrument.
give
approximately
nine
months
continuous
operation.
Alternatives:
These
will
Four
HP7,
V12
or
D14
(AA)
batteries.
With
these
alternatives
the
battery
life
will
be
reduced
to
approximately
three
months
continuous
operation.
-10 -
6.
REMOVAL
OF
THE
PANEL
FROM
THE
CASE
(Plate
1)
If
it
is
necessa~
to
open
the
instrument
(see
notes
which
follow
regarding
fault
finding)
it
should
be
placed
on
the
bench
front
panel
downwards
and
the
Instruction
Plate
removed
as
above
together
with
the
four
additional
screws
(items
16
and
23)
in
the
base
of
the
case.
A
heated
screwdriver
facilitates
removal
of
the
wax
seal.
The
case
can
now
be
lifted
off
to
lie
alongside
the
panel,
taking
care
not
to
break
the
batte~
connections.
To
completely
remove
the
case
the
batte~
connections
should
be
disconnected.
Take
particular
note
of
these
connections
in
order
that
they
can
be
correctly
connected
after
repair.
When
replacing
the
four
screws
in
the
base
of
the
case
ensure
that
these
are
not
over-tightened
as
this
could
cause
damage
to
the
case.
7.
REMOVAL
OF
THE
PRINTED
CIRCUIT
RANGE
OOARD
(Plate
1)
This
board
is
immediately
visible
after
removal
of
the
case.
Remove
the
two
screws
(item
15)
which
will
enable
the
moulded
bar
(item
14)
to
be
removed.
Take
particular
care
not
to
lose
the
nylon
washers.
Unscrew
the
short
hexagon
pillar
(item
10)
and
unsolder
the
two movement
connecting
wires
from
the
printed
circuit
board.
These
are
the
two
flexible
leads
soldered
to
the
line
of
the
connectors
at
the
bottom
edge
of
the
board.
The
board
can
now
be
lifted
off,
but
to
completely
free
the
board,
all
connections
to
the
board
will
have
to
be
unsoldered.
Note
position
of
these
connections.
Particular
care
must
be
taken
when
lifting
off
the
board
to
gently
ease
the
board
off
the
switch
spindle.
It
has
been
found
that
exerting
slight
pressure
with
the
thumbs on
the
black
switch
arm
enables
the
board
to
be
lifted
off
without
difficulty.
Any
washer
underneath
the
hexagon
pillar
(item
10)
should
be
replaced
when
the
board
is
re-assembled.
If
there
is
no
washer
it
is
not
required.
Note:
these
are
packing
washers
and
it
is
essential
that
they
are
replaced
in
their
original
position.
Individual
components on
this
board
can
be
readily
replaced
after
identi-
fication.
If
however,
it
is
necessa~
to
remove
the
slide
switch,
some form
of
solder
removing
iron
will
be
required.
When
servicing
printed
circuit
boards
great
care
is
required
to
ensure
that
the
minimum
of
solder
is
used
as
excessive
solder
could
cause
short
circuits.
After
any
repair
work on
the
printed
circuit
boards
all
residue
flux
and
dirt
must
be
cleaned
off.
8.
REMOVAL
OF
THE
AMPLIFIER
BOARD
(Plate
1)
After
removal
of
the
case
and
the
Range
Board,
remove
the
screening
plate.
To
do
this,
remove
the
bakelite
washer
from
the
switch
spindle
and
the
three
round
headed
screws.
Take
particular
care
of
these
screws
as
it
is
essential
that
round
headed
screws
are
used
when
the
screening
is
replaced.
Care
should
be
taken
not
to
exert
too
much
pressure
on
the
black
washer
on
the
switch
spindle
as
this
will
distort
the
switch
contacts.
-
11
-
The
covers
must
be
removed from
the
Ohms
and
Centre
Zero
Adjuster
and
the
Operating
Mode
control
mounted on
the
front
pa~el
(items
7
and
8).
Note
the
position
of
the
battery
check
control
in
order
that
when
replacing,
the
arrow
on
this
switch
is
replaced
in
the
correct
position.
Remove
the
grub
screws
from
the
metal
inserts
using
Allan
Key
No.K11
and
remove
the
inserts
from
the
spindles.
After
unsoldering
all
connections
to
this
board,
it
can
be removed. The
circuitry
can
easily
be
traced
as
all
components
on
the
board
are
identified
by
their
circuit
references.
The
notes
regarding
the
servicing
of
printed
circuit
boards
in
Section
7
should
be
observed.
9.
REMOVAL
OF
THE
MOVEMENT
FRDM
THE
PANEL
(Plate
1)
Unless
it
is
absolutely
essential
the
movement
should
not
be
disturbed
and
the
movement
cover
should
remain
in
place.
If
it
is
really
necessary
to
remove
the
movement,
the
following
instructions
should
be
carefully
followed.
Having
removed
the
case
and
the
printed
circuit
boards
remove
the
movement
cover
and
unsolder
the
connections
to
the
movement
assembly.
The two
screws
and
nylon
washers
(items
20
and
21)
should
be
removed
together
with
the
two
scaleplate
retaining
screws
(item
28).
The
complete
movement
assembly
may
now
be
lifted
from
the
panel.
Take
particular
care
of
the
nylon
washers
and
when
they
are
replaced
ensure
that
they
are
securely
screwed
down.
The movement
is
such
a
specialised
item
that
in
the
event
of
defects
of
more
than
a
minor
nature,
it
is
recommended
that
a
complete
replacement
should
be
used.
If
repairs
to
the
movement
are
necessary
it
must
be
de-magnetised
before
any
repairs
can
be
carried
out
and
after
repair
the
sensitivity
will
have
to
be
adjusted
as
in
Section
12.
The
scaleplate
may
need
replacement
and
re-calibration
to
regain
the
original
a:ccuracy.
Re-balancing
will
be
necessary
and
the
magnet
will
have
to
be
re-magnetised
when
repairs
are
complete.
The
associated
movement
board
is
readily
visible
after
removal
of
the
amplifier
board.
Remove
the
screws
securing
this
to
release
the
board.
To
replace
the
movement
the
procedure
outlined
above
should
be
reversed.
Care
must
be
taken
to
ensure
that
the
zero
adjuster
screw
engages
with
the
slot.
-12 -
FAULT
FINDING
AND
SERVICING
INFORMATION
10.
FAULT
FINDING
TABLE
The
following
table
is
given
to
assist
in
the
rapid
location
of
a
fault.
Comprehensive
servicing
details
follow.
See
Section
11
(a)
to
(r)
inclusive.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(j)
(k)
(m)
(n)
(p)
(q)
SYMPTONS
No
reading
on
any
range
or
intermittent
reading
only.
No
reading
on
an
isolated
current,
voltage
or
resistance
range.
No
d.c.
voltage
or
current
reading.
One
or
more
d.c.
current
or
voltage
ranges
inoperative.
Incorrect
or
no
reading
on
a.c.
but
correct
on
d.c.
Ohms
range
inoperative,
intermittent
or
incorrect.
Inability
to
attain
ohms
full
scale
setting
or
drifts
shortly
after
being
set.
Unable
to
adjust
to
centre
zero.
Low
readings
on
all
current
and
voltage
ranges.
Pointer
sticks
at
one
particular
point.
Pointer
stuck
firmly.
Slight
uniform
pointer
stick
over
the
whole
scale.
Incorrect
readings
on low
a.c.
ranges,
pointer
swings
to
f.s.d.
on
switching
on.
Instability
of
readings.
PROBABLE
FAULT
Leads
open
circuit
or
intermittent,
faulty
fuse
or
switch
fault.
Moving
coil
open
or
short
circuit.
A
faulty
connection
between
switch
contact
or
ranging
resistors.
Faulty
d.c.
amplifier.
One
or
more
ranging
resistors
faulty.
Suspect
a
faulty
a.c.
amplifier
or
ac/dc
switch.
Pos~ible
fault
ln
the
constant
current
circuitry.
Possible
battery
failure
or
fault
ln
constant
current
circuit.
Battery
fault
or
constant
current
circuit
faulty.
Battery
failure
or
amplifiers
faulty.
Amplifier
faulty
or
dust,
hair
or
other
foreign
body
fouling
the
movement.
Pivot
out
of
jewel.
Tight
in
jewels,
blunted
pivots,
dirt
in
jewels
or
possible
damaged
jewels.
Prods
not
making good
contact.
Metallic
coating
inside
case
not
satisfactorily
earthed.
(r)
Pointer
moves from
position
Movement
out
of
balance.
of
rest
by
more
than
1%
of
the
maximum
scale
value
when
the
instrument
is
&eld
in
any
position
within
45 from
normal.
-13
11.
SERVICING
INFORMATION
To
enable
the
most
suitable
method
of
repair
to
be
selected
the
information
obtained
from
the
Table
in
(10)
should
be
carefully
considered
together
with
any
information obtained
from
Section
4
and
the
servicing
information
which
follows
this
section.
It
must
be
emphasised
that
due
to
the
constant
voltage
characteristic
of
the
batteries
supplied
with
the
instrument,
the
voltage
falls
rapidly
at
the
end
of
life.
This
fact
should
be
borne
in
mind
whilst
attempting
to
trace
faults
in
the
circuit
and
the
batteries
should
be
checked
at
suitable
intervals.
The
information
in
this
section
is
cross-referenced
to
the
alphabetical
sequence
in
the
fault-finding
table
i.e.
if
the
symptom
and
possible
fault
appear
at
(f)
in
the
fault-finding
table,
the
relevant
servicing
information
will
be
found
at
(f)
in
this
section~
It
must
be
emphasised
that
before
servicing
can
be
carried
out
on
the
movement
it
must
be
de-magnetised.
(a)
No
reading
on
any
range
or
intermittent
reading
only
The
leads
should
be
checked
for
open
circuit
and
the
fuse
examined.
If
neither
are
faulty
check
for
open
or
short
circuit
meter
movement.
(b)
No
reading
on
an
isolated
Current,
Voltage
or
Resistance
range
If
only
one
range
is
found
to
be
at
fault,
the
ranging
resistors
associated
with
that
particular
range
should
be
checked.
The
connections
between
the
relevant
switch
contact
and
the
shunt
or
multiplier
concerned
should
be
checked
with
an
ohmmeter
to
see
if
there
is
a
dry
joint
and
correction
made
as
necessary.
(c)
No
d.c.
voltage
or
current
readings
(or
erratic
readings)
The
fault
will
almost
certainly
be
in
the
d.c.
amplifier
and
this
should
be
tested
in
accordance
with
the
test
specification
in
Section
17.
(d)
One
or
more
d.c.
voltage
or
current
ranges
inoperative
One
or
more
shunt
or
multiplier
resistors
may
be
faulty.
(e)
Incorrect,
or
no
reading
on
a.c.
but
is
correct
on
d.c.
This
fault
will
almost
certainly
be
caused
by
a
defective
a.c.
amplifier
and
this
should
,b.e
tested
in
accordance
with
the
test
specification.
(See
Section
18).
Alternative.ly
this
fault
may
be
due
to
a
faulty
ac/dc
switch
and
this
should
also
be
checked.
-
14
-
(f)
Ohms
range
inoperative,
intermittent
or
incorrect
If
the
ohms
range
is
inoperative
or
incorrect,
VT11
and
associated
circuitry
should
be
checked.
If
the
ohms
ranges
have
been
overloaded
R62,
R63
or
associated
circuitry
could
be
damaged.
(g)
Inability
to
attain
ohms
full
scale
setting
or
drifts
shortly
after
being
set
Check
VT11
and
associated
circuitry.
(h)
Unable
to
adjust
to
centre
zero
The
batteries
should
be
checked
but
if
these
are
satisfactory
VT11
and
associated
circuitry
should
be
checked.
(j)
Low
readings
on
all
current
and
voltage
ranges
If
batteries
are
satisfactory
check
both
a.c.
and
d.c.
amplifiers
as
outlined
ln
the
test
specification.
See
Sections
17
and
18.
(k)
Pointer
stick
at
one
particular
point
This
sympton
often
indicates
that
dust,
a
small
piece
of
iron
or
some
other
foreign
body
is
possibly
fouling
the
moving
coil
former.
Specks
of
dust
or
even
a
hair,
if
present,
can
be
removed
with
a
fine
needle.
A
minute
hair
on
the
scaleplate
or
on
the
window
glass
could
cause
sticking
and
this
may
only
show
up
in
a
bright
light.
In
all
such
cases
sticking
might
also
be
dependent
upon
a
slight
tilt
of
the
instrument
associated
with
the
small
but
essential
pivot
play.
Should
the
fault
not
be
cleared
check
the
amplifiers
as
out-
lined
in
the
appropriate
test
specification.
Unless
it
is
essential
the
movement
should
not
be
dismantled.
(m)
Pointer
stuck
firmly
It
can
occasionally
happen
that
severe
mechanical
shock
can
cause
a
pivot
to
leave
its
jewels
and
become
lodged
in
the
end
of
a
jewel
screw,
which
would
result
in
the
pointer
becoming
firmly
stuck.
Do
not
try
to
push
the
pivot
back
as
damage
will
occur.
A
slight
re-adjustment
of
both
top
and
bottom
jewel
screws
may
cure
the
fault,
but
if
it
still
persists,
the
moving
coil
assembly
will
have
to
be
replaced.
-15 -
(n)
Slight
uniform
pointer
stick
over
the
whole
scale
This
may
be
due
to
a
slight
tightening
of
the
moving
coil
between
the
spring
mounted
jewels.
With
the
movement
horizontal
a
minute
clearance
between
the
top
jewel
and
pivot
should
permit
of
a
slight
sideways
rock.
The
jewel
assembly
will
show a
sideways
rock
if
adjustment
is
too
tight,
due
to
the
jewel
being
raised
from
its
seating.
The movement
in
such
a
case,
would show a
peculiar
change
of
swing
just
before
coming
to
rest
and
furthermore,
the
instrument
held
on
its
side
might
also
show
complete
instability
of
zero
reading.
Slightly
easing
the
top
jewel
screw
will
indicate·
if
this
:is
the
cause
of
friction
and
effect
a
cure.
If
this
type
of
stick
cannot
be
cured
by
jewel
screw
adjustment
it
will
be
necessary
to
dismantle
the
movement
for
repair
or
replace
it
completely.
(p)
Incorrect
readings
on
low
a.c.
ranges,
pointer
swings
to
f.s.d.
on
switching
on
This
may
be due
to
the
fact
that
the
prods
are
not
making good
contact
and
this
should
be
checked.
(q)
Instability
of
readings
The
metallic
coating
inside
the
case
is
earthed
through
the
battery.
If
readings
appear
to
be
unstable
check
that
this
earthing
lead
is
satisfactory.
This
is
the
black
lead
connected
directly
between
Range
board
and
negative
terminal.
(r)
Movement
out
of
balance
The moving
coil
is
balanced
when
the
instrument
leaves
the
factory
but
very
severe
overload,
mechanical
shock
or
pivot
damage,
may
cause
it
to
become
unbalanced.
The
balance
limit
permitted
in
BS
89
allows
a
pointer
change
of
+
1%
of
maximum
scale
values
when
the
instrument
is
held
in
any
position
within
45°
from
horizontal.
If
the
movement
needs
re-balancing,
it
should
be mounted
in
a
dr~ught-proof
box
and
tested
in
four
positions
with
the
axis
horizontal
for
tests
2,
3
and
4:
(
1)
Set
the
pointer
to
zero
with
the
instrument
in
a
horizontal
position.
(2)
Check
zero
position
with
pointer
horizontal
and
pointing
left.
(3)
Check
zero
position
with
pointer
horizontal
and
pointing
right.
(4)
Check
zero
position
with
the
pointer
vertical
upwards.
The
balancing
box
should
be
tapped
lightly
during
balancing
operations
to
ensure
that
pivot
friction
does
not
interfere
with
the
balance
effect.
If
a
satis-
factory
balance
cannot
be
achieved,
the
pivots
will
almost
certainly
be
defective.
If
a new
coil
is
fitted
major
balancing
is
called
for.
The
balancing
of
an
instrument
calls
for
a
high
degree
of
skill
and
once
again
we
advise
that
if
the
trouble
is
difficult
to
cure,
the
whole
movement
assembly
should
be
replaced.
-
16
-
DISMANTLING
AND
REPLACEMENT
12.
DISMANTLING
THE
MOVEMENT
(Plate
2)
If
adequate
facilities
and
skill
are
available
for
major
movement
repair,
certain
spares
are
available.
The moving
coil
complete
with
pointer,
hairsprings
and
pivots
can
be
supplied,
but
the
replacement
of
such
a
unit
in
the
movement,
requires
care
and
will
necessitate
adjustment
of
the
sensitivity
to
36-37~,
recali-
bration
and
also
the
possible
replacement
of
the
scaleplate
in
order
to
regain
the
original
accuracy.
The
fitting
of
a new moving
coil
will
also
necessitate
the
re-balancing
of
the
movement
whilst
the
magnet
will
have
to
be
re-magnetised
and
aged
before
the
correct
sensitivity
can
be
met.
If
a movement
is
changed
always
ensure
that
any
serial
number marked on
the
scaleplate
is
transferred
to
the
scaleplate
of
the
replacement
movement. The
defective
movement
can
be
returned
and
allowance
will
be made
for
any
useful
component
parts.
The
following
notes
are
given
to
assist
in
the
dismantling
and
repair
of
the
movement:
Having removed
the
movement from
.the
panel
assembly
(see
Section
9)
remove
the
scaleplate
from
the
movement.
Before
any
further
work
is
carried
out,
the
magnet
must
be
de-magnetised.
This
can
best
be
done
with
the
use
of
the
Avo
Magnetising
Unit
which
is
available
from
Avo
Limited.
The movement
should
then
be
dismantled
in
the
following
order:
First
remove
the
reversing
switch
bar
(item
11).
(item
14),
hinge
the
bar
free
from
the
reversing
switch
from
the
fulcrum
pin
(item
3/1).
To
do
this
remove
the
circlip
spindle
and
withdraw
sideways
Unsolder
the
outer
ends
of
the
two
hairsprings
and
disconnect
the
connections
from
the
top
and
bottom
zero
adjuster.
NOTE:
When
dismantling
it
is
essential
that
a
note
is
made
of
the
magnet
axis
identification
mark
as
it
is
important
that
the
magnet
be
re-assembled
with
the
axis
in
the
original
position.
With
item
4
uppermost
and
item
5
in
the
centre
scale
position,
place
the
move-
ment on
assembly
jig
Avo
Part
No.
AF
5075.
Remove
the
two
screws
(items
8
and
9).
Press
items
1
and
2
firmly
downwards
against
the
assembly
jig
and
remove
item
4
by
gently
levering
upwards.
NOTE:
Items
1,
2,
3
and
4
are
assembled
with
LOCTITE
retaining
compound (Green)
and
care
must
be
exercised
when
dismantling
these
items.
-17 -
Press
item
2
firmly
down
against
the
assembly
jig
and
remove
item
1
by
pulling
upwards.
Press
item
3
firmly
down
against
the
assembly
jig
and remove
items
2 and 5 from
the
jig
by
pulling
upwards.
Separate
items
2
and
5.
Remove
item
3 from
the
jig.
Remove
all
traces
of
retaining
compound from
items
1,
2,
3
_and
4.
Unlock
and
slacken
back
the
jewel
screws
on
items
3
and
4
so
that
the
face
of
the
screw
is
flush
with
the
inside
face
of
the
bridge
piece.
Parts
may
now
be
examined
and
cleaned
as
follows:
Sticking
can
be
due
to
dust
or
rustlike
deposition
which
sometimes forms on
the
tip
of
the
pivot
and
in
the
jewel
and
it
may
be
worthwhile
seeing
if
its
removal
cures
the
stick
rather
than
replace
the
movement
or
parts.
If
a
microscope
is
avail-
able
(having
a
magnification
of
X100
or
better)
place
the
·jewel
screw
on
the
table
with
the
jewel
uppermost,
illuminate
well
and
examine.
It
is
very
difficult
to
diagnose
small
mechanical
damage
optically,
but
the
presence
of
foreign
matter
such
as
red
deposit
arising
from wear
is
readily
apparent.
The
jewels
can
be
cleaned
using
a
piece
of
pegwood
cut
with
a
very
sharp
knife
or
razor
blade
to
a
diameter
which
will
enter
the
end
of
the
jewelscrew.
The
tip
must be
brought
to
a
very
fine
point
and
there
must be no
loose
fibres
left.
Soak
the
jewel
in
Trichlorethylene
and
holding
the
jewel
downwards, wipe
the
interior.
Brush
the
jewel,
still
inverted·,
with
a
fine
dry,
clean
pencil
brush
and
then
examine
the
jewel
under
the
microscope
in
a good
light
to
ensure
that
all
rustlike
deposit
or
other
foreign
matter
has
been
removed.
If
cracks
are
detected
the
jewel
must be
replaced.
Sticking
could
also
be
caused
by
a damaged
pivot.
The
pivot
should
be
examine~
under
a
microscope
and
if
it
should
require
cleaning
this
can
be done
by
rotating
the
end
of
a
piece
of
impregnated
pegwood on
the
pivot
tip
and
then
pressing
it
into
a
piece
of
cork
or
pith.
Re-examine
the
pivot
to
see
if
it
can
be
used
or
if
it
should
be
replaced.
An
undamaged
tip
should
have a
spherical
radius
of
.0004
in.
If
any
departure
from
the
spherical
shape
is
evident
or
if
its
radius
has
become
excessive
a
replacement
moving
coil
assembly
will
be
req~ired.
If
a
jewel
screw
is
rested
on
the
tip
of
the
pivot,
the
clearance
between
the
end
of
the
screw
and
the
pivot
holder
should
be
in
the
order
of.012
in.
This
can
determine
the
maximum
jewel
retraction
under
the
influence
of
impact.
A damaged
jewel,
(which
is
a most
infrequent
occurrence)
must
always
be
replaced
by
a
similar
one
supplied
in
its
spring
mounting.
Before
re-assembling,-
items
8 and 9
should
be renewed.
To
re-assemble
the
movement,
reverse
the
dismantling
procedure,
but
do
not
replace
the
reversing
switch
bar
(item
11).
Ensure
that
item
2
is
replaced
with
the
identification
mark
in
the
original
position.
Tighten
item
8
with
a
torque
screw-
driver
to
4
in.
lb.
-18 -
Remove
the
assembly
from
the
jig
and
inject
LOCTITE
retaining
compount
(Green)
into
the
mating
surfaces
of
items
1,
2,
3
and
4,
taking
care
that
the
liquid
does
not
contaminate
item
5.
Solder
the
outer
tails
of
the
hairsprings
to
the
zero
adjuster
tags
and
reconnect
the
circuit
wires
to
the
top
and
bottom
zero
adjusters.
Replace
the
scale-
plate.
IMPORTANT
NOTE.
Each movement
is
individually
calibrated
and
is
matched
to
a
scale-
plate
of
a
particular
characteristic.
If
the
movement
is
repaired
and
is
not
re-cali-
brated
it
must
be
recognised
that
the
accuracy
will
almost
certainly
be
impaired.
Balance
the
movement
to
within+
1%
of
f.s.d.
Gently
rotate
the
spindle
of
Potentiometer
RV3
(22k~J)
in
a
counter-~lockwise
direction
until
the
end-stop
position
is
reached.
Re-charge
the
magnet
circuit
to
give
a
full
scale
current
sensitivity
of
approximately
33~.
Carefully
discharge
the
magnet
circuit
until,
with
the
pointer
resting
at
full
scale,
the
current
sensitivity
is
between
37.7
and
38.1~.
NOTE:
During
the
discharge
procedure
make
frequent
checks
to
ensure
that
the
pointer
rests
on
the
scale
zero
when no
current
flows.
0
Stove
the
complete
assembly
for
10
hours
at
70 C
and
then
allow
to
stabilise
for
10
to
14
days
at
15
to
25°C.
At
the
completion
of
this
period
check
the
side
and
end
clearance
of
the
movement
and
adjust
if
necessary.
Check
the
movement
for
freedom
from
stick
or
foreign
matter
in
both
horizontal
and
vertical
positions.
Set
the
top
zero
adjuster
in
the
central
position
and
set
the
bottom
zero
adjuster
to
bring
the
knife
edge
pointer
exactly
over
the
scale
zero.
Re-balance
the
movement
to
within+
0.5%
of
f.s.d.
Pass
37.5~
through
the
movement
and
adjust
the
22kQ
potentiometer
to
bring
the
pointer
to
full
scale
+ 0.2%
of
f.s.d.
Check
all
cardinal
points
on
the
scale
for
correct
current
sensiti~ity.
The
reversing
switch
bar
may
now
be
replaced
and
the
movement
re-assembled
on
the
panel
assembly
using
the
reverse
procedure
to
that
described
in
Section
9.
13.
FRONT
PANEL
REPLACEMENT
(Plate
3)
Having
removed
the
Range
and
Amplifier
printed
circuit
board
assemblies
(see
Sections
7
and
8)
and
the
Movement
assembly
(Section
9)
the
remainder
of
the
front
panel
components
must
be
transferred
to
the
replacement
front
panel.
This
should
be
carried
out
as
follows:
-19 -
Remove
the
switch
knob
circlip
(item
10).
This
will
requ~e
a
pair
of
special
circlip
pliers.
Care
should
be
taken
not
to
lose
the
click
balls
or
springs
located
between
knob
and
panel.
Remove
the
slide
switch
bar
clips
{item
24)
again
these
can
be
cut
as
new
ones
are
provided.
The
whole
of
the
changeover
switch
mechanism
can
now
be
lifted
out
of
the
panel.
Remove
the
zero
adjuster
retaining
clip
(item
14)
and
the
zero
adjuster
knob
from
the
panel.
Remove
the
two
terminals
by
unscrewing
the
nuts
(item
19)
using
a
5/16
in.
BSF
spanner.
These
items
may
now
all
be
re-assembled
on
the
replacement
front
panel
assembly
using
the
new
spring
retainers
where
provided.
See
Plate
3
for
gear
wheel
assembly
instructions.
14.
R.EPLA.CEMENT
OF
SLIDE
SWITCH
ASSEMBLY
This
may
be
removed. from
the
printed
circuit
board
if
care
is
taken.
Using
a
solder
removing
iron,
unsolder
each
connection
in
turn,
making
sure
that
sufficient
solder
is
removed.
to
release
the
connections
from
the
board.
When
replacing,
care-
fully
remove
solder
from
the
holes
on
the
board
to
which
the
connections
must
be
soldered.
This
can
best
be
carried
out
using
a vacuum
de-soldering
tool,
but
if
this
is
not
available
the
solder
should
be
melted
and
the
holes
cleaned
by
a
sharp
blast
of
air.
Take
the
new
slide
switch
and
solder
all
connections
to
the
appropriate
points.
-
20
-
ELECTRICAL
TESTING
15.
TRANSISTOR
SELECTION
PROCEDURE
F.E.T.
Selection:
Should
it
be
necessary
to
replace
either
VT1
or
VT12
one
having
the
correct
characteristics
will
be
necessary
and
selection
will
be
required.
A
suitable
test
circuit
is
shown
in
Fig.
1
which
will
enable
this
selection
procedure
to
be
carried
out.
The
selection
procedure
is
as
follows:
(a)
With
the
Supply
switch
at
OFF
turn
the
potentiometer
knob on
the
test
gear
fully
clockwise.
(b)
Connect
the
F.E.T.
to
be
tested
and
switch
ON.
(c)
Rotate
the
potentiometer
anti-cloCkwise
until
a
reasonable
reading
is
obtained,
then
rotate
the
potentiometer
clockwise
until
the
meter
just
reads
1~.
(d)
The
position
of
the
potentiometer
will
now
indicate
whether
the
F.E.T.
is
suitable
for
use
for
the
d.c.
amplifier,
the
a.c.
amplifier
or
whether
it
is
to
be
rejected.
(As
indicated
on
the
drawing
the
potentiometer
must
first
be
calibrated
and
the
divisions
marked
appropriately.)
NOTE:
An
F.E.T.
selected
for
the
d.c.
amplifier
may
be
used
in
the
a.c.
amplifier,
but
an
F.E.T.
selected
for
the
a.c.
amplifier
cannot
be
used
in
the
d.c.
amplifier.
Selection
of
BC.183 1s
for
a.c.
amplifier:
Transistors
for
use
in
positions
VT14
and
VT15
must
be
gain-selected
in
order
to
eliminate
offset
zero
readings
on
a.c.
functions.
Similarly
transistors
for
use
in
VT5
and
VT6
positions.
require
gain-selection
to
ensure
that
the
d.c.
amplifier
zero
can
be
set
within
the
range
of
RV4.
Using
a
Transistor
Test
Set
Type TT.166,
check
the
gain
of
the
transistors
type
BC.183
for~
at
an
IC
of
10~.
Select
those
with
an
~E
between
200
and
300,
for
use
in
VT5,
vf~,
VT14
and
VT15
positions.
Yield
should
be
about
40%.
16.
GENERAL
FUNCT
ION.AL
CHECK
To
ensure
that
the
instrument
is
now
functioning
the
brief
checks
outlined
in
Section
4
should
be
carried
out
before
detailed
checks
on
the
a.c.
and
d.c.
amplifiers.
17.
D.C.
CALIBRATION
TESTS
AND
ADJUSTMENTS
(a)
With
the
Range
switch
set
to
the
OFF
position,
set
the
Operating
Mode
switch
to
Battery
+ve
and
depress
the
a.c.
push-button.
(b)
Check
mechanical
zero
and
adjust
if
necessary.
-
21
-
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Other AVO Measuring Instrument manuals
