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Model
3484A
twisted.
Dirt
or
contamination
on
the surface
of
the
glass-enclosed 20
kilomegolun
resistor will
tend
to
reduce
input
resistance on
the
three lower
ranges.
Teflon
parts
on
any
assembly
must not
be touched
with
the hands.
5-27.
Component
Replacement.
The
following
general
rules
should
be
observed
when
replacing components
on
the
Attenuator
and
Amplifier
assemblies
or
the
upper
left
quarter of
the Range assembly.
Figure
5-7 illustrates
methods for
avoiding
contamination
when
replacing
components
on
a clean
assembly.
I
.
Handle components
and asse mblies only
with
clean
gloves
or
clean tools,
or
handle
printed circuit
boards
by
touching
on
ly
the edges.
2. Lay
printed circuit board
on
a
clean
surface,
pre-
fe
rably
a
hard,
flat
surface.
3. Do
not
use
solder on or
near the printed
circuit
boa
rd;
flux
will
contaminate the surface. Component
leads
should
be tinned
away
from
the vicinity of
the
board.
4.
Do not
use a
solder removing tool. Leave
old
solder
in
the hole.
5. The soldering
iron should
be
cleaned before
each
use
by wiping
on
a
wet
sponge.
6.
Always apply
soldering
iron heat
to
component
side
of
printed circuit
board.
5·28.
REED
REPLACEMENT.
5-29.
Recd
switches
must be handled very
carefully.
Clean
rubber
gloves or
fin ger
cots
must
be worn
,
or the reed
must
be
handled by
the
metal
leads
only.
When
replacing
reed
switches,
be
careful not
to
bend
the leads. Stress
on
the
leads
may break the glass
seal
or
cause the
switch to be
inoperative.
The leads of most
replacement
reed
switches
must
be
shortened
by cutting
an
equal
amount
from each
lead,
so
that the total length is
I·
7/16
inches.
Use
longnose
pliers
to hold
the
lead
between the
glass
envelope and the
cutting
tool to
avoid
damaging
the
glass to metal
seal.
5-30. Some
reeds
in the
3484A
are
soldered in place, while
others are
inserted into
spring
clips.
A
special tool, -hp·
Part
No. 4040-0720,
is
provided with
the
3484A
fo
r
the purpose
of
removing
and replacing
reed
switches
which
use the
spring clips. Figure
5-8 shows
the proper
use of
the reed
replacement tool.
5-31.
DC AMPLIFIER ASSEMBLY REPAIR AND
EX·
CHANGE.
5-32.
Certain components associated
with
the
differential
amplifier
stage
are factory
selected to
provide
proper
operation
of
the
amplifier
under
temperature
variations.
Jf
A21Cl, A2Q2, A2Q8, or A2Ql4, for example,
must
be
Section
V
3482A·
B-303~2
Figure
5·8.
Reed Removal and Replacement.
5-9
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