Maintenance
—
Type
502A
Fig.
4-6.
Soldering
to
a
terminal
mounted
in
plastic.
Note
the
use
of
the
long-nosed
pliers
between
the
iron
and
the
coil
form
to
absorb
the
heat.
Fig.
4-7.
The
ceramic
strip
and
its
parts.
NOTE
Considerable
force
may
be
necessary
to
push
the
mounting
posts
into
the
nylon
collars.
Be
sure
that
you
apply
this
force
to
that
area
of
the
ceramic
strip
directly
above
the
mounting
posts.
TROUBLESHOOTING
PROCEDURE
This
section
of
the
manual
contains
information
for
trouble
shooting
your
oscilloscope.
Before
attempting
to
trouble
shoot
the
instrument,
however,
make
sure
that
any
apparent
trouble
is
actually
due
to
a
malfunction
within
the
instrument
and
not
to
improper
control
settings.
Instructions
for
the
operation
of
the
oscilloscope
are
contained
in
the
Operating
Instructions
section
of
this
manual.
Tube
failure
is
the
most
prevalent
cause
of
circuit
failure.
For
this
reason,
the
first
step
in
troubleshooting
any
circuit
in
the
instrument
is
to
check
for
defective
tubes,
preferably
by
direct
substitution.
Do
not
depend
on
tube
testers
to
adequately
indicate
the
suitability
of
a
tube
for
certain
positions
within
the
instrument.
The
criterion
for
usability
of
a
tube
is
whether
or
not
it
works
satisfactorily
in
the
instru
ment.
Be
sure
to
return
all
good
tubes
to
their
original
sockets;
if
this
procedure
is
followed
less
recalibration
of
the
instrument
will
be
required
upon
completion
of
the
servicing.
When
replacing
any
tube
in
the
instrument,
check
first
to
see
that
components
through
which
the
tube
draws
current
have
not
been
damaged.
Shorted
tubes
will
some
times
overload
and
damage
plate-load
and
cathode
resistors.
These
damaged
components
can
generally
be
located
by
a
visual
inspection
of
the
wiring.
If
no
damaged
components
are
apparent,
and
if
tube
replacement
does
not
restore
operation,
it
will
be
necessary
to
make
measurements
or
other
checks
within
the
circuit
to
locate
the
trouble.
The
component
number
of
each
resistor,
inductor,
capac
itor,
vacuum
tube,
control
and
switch
is
shown
on
the
circuit
diagrams.
The
following
chart
lists
the
component
numbers
associated
with
each
circuit:
All
numbers
less
than
100
......................................
Time-Base
Trigger
100
series
.....................................
Time-Base
Generator
300
series
.......................................
Horizontal
Amplifier
400
series
................................
Upper
and
Lower
Beam
Vertical
Amplifiers
700
series
...........................................
Low-Voltage
Powe
r
Supply
800
series
...........................
CRT
Circuits,
High
Voltage
and
Amplitude
Calibrator.
Switch
wafers
shown
on
the
schematic
diagrams
are
coded
to
indicate
the
position
of
the
wafer
on
the
actual
switches.
The
number
position
of
the
code
refers
to
the
wafer
number
on
the
switch
assembly.
Wafers
are
numbered
from
the
front
of
the
switch
to
the
rear.
The
letters
F
and
R
indicate
whether
the
front
or
the
rear
of
the
wafer
is
used
to
perform
the
particular
switching
function.
CIRCUIT
TROUBLESHOOTING
Although
the
Type
502A
is
a
complex
instrument,
it
can
be
thought
of
as
consisting
of
six
main
circuits,
in
addition
to
the
Calibrator
circuit.
These
are
the:
1.
Low-Voltage
Power
Supply
2.
CRT
Circuit
and
High-Voltage
Power
Supply.
3.
Vertical
Amplifiers.
4.
Time-Base
Trigger
Circuit.
5.
Time-Base
Generator.
6.
Horizontal
Amplifier.
The
first
circuit
to
check,
for
practically
any
type
of
trouble,
is
the
Low-Voltage
Power
Supply.
Because
of
the
circuit
configuration
employed,
it
is
possible
for
an
improper
power
supply
voltage
to
affect
one
circuit
more
than
the
others.
For
example,
if
the
gain
of
the
Vertical
Amplifier
should
decrease
slightly,
while
the
other
circuits
appear
to
be
functioning
normally,
this
could
be
due
to
an
im
proper
supply
voltage
and
not
to
any
condition
originating
in
the
Vertical
Amplifier.
In
cases
of
this
type,
valuable
can
be
saved
by
checking
the
power
supply
first.
4-3
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