Maintenance; Access Instructions; Calibration Instructions - Wavetek 142 Instruction Manual

SECTION
T
MAINTENANCE
4.1
ACCESS INSTRUCTIONS
Removal
of the
dust cover affords
quick access to the
majority of
components within the
unit.
However,
it
may
be necessary to
remove
the
Power Supply Board
or
other
parts to gain access
to those
components not exposed
by
removing the dust cover.
4.1.1
Removing
the dust cover
To remove the dust cover
(case)
from
the
Model
142,
the
following
procedure should be
followed:
1.
Unplug
the
power cord
and unscrew
the
two
captive
screws
on the
rear panel.
2.
Remove
the
rear
casting
and, with
the
instrument
setting face
down,
lift
the cover off slowly.
3.
Reverse
this
procedure
when
replacing
the dust cover.
Tighten the
two
captive
screws only finger-tight.
4.1.2
Removing
the
Power Supply Board
1.
Remove two
screws holding the
Power Supply
Board
to
the
two
side panels.
2.
Loosen the
two screws (from the outside of the
rear
plate)
which hold the heat sink for the four
power
supply transistors.
3.
Flip
the
Power Supply Board out of the
chassis,
toward
the
rear,
and
mount
the board
on
the outside of the
rear plate using
the
same two
screws and the
same two
holes
used to
mount
the heat sink.
NOTICE
This instrument can be operated with the
power
supply board
mounted on
the outside of the
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without
having the heat
sink
of the
power
supply
board connected
to
the
rear plate
of the
unit,
as
the
rear plate
is
also
used
as a
portion of the
heat sink for the
power
transistors.
NOTICE
4.1.3
Switch Bracket
Removal
1.
Remove
the four front panel
knobs
labeled
OUTPUT
ATTEN, DC
OFFSET,
SYMMETRY,
and
DC OFFSET
MIN/MAX.
2.
Unsolder the
wire
connected to the 50f2
OUT
connector.
3.
Loosen and remove
the
two
screws
which
attach
the
switch bracket to the
main
circuit
board,
and
slide
bracket
out toward the
rear.
4. If
necessary, unsolder the other wires
connected to the
switches.
4.1.4
Replacing
Q54
and
Q55
1.
The
base of the transistor
heat sink
is
permanently
secured
with thermally conductive expoxy onto the
front panel
casting.
To
remove
the transistor,
unscrew
the nuts holding the
transistor
to the base of the heat
sink
and
unsolder the transistor leads
on
the
main
circuit board.
Then remove
transistor.
2.
Before
replacing
the
transistor,
put
some
thermal
com-
pound
or
silicon
grease along both
sides
of the
bottom
edge of the
transistor
for
good thermal
contact.
4.1.5
Front
Panel
Removal
1
.
Remove
the
rear
panel
and
dust cover as
described above,
and unplug
all
the knobs.
2.
Unsolder
all
BNC
connectors,
lable
and unsolder
FRE-
QUENCY
DIAL
potentiometer
leads,
and unscrew the
two
nuts
which hold the
power
transistors into
the heat
sinks.
3.
Remove
bulb
from
the indicator lamp,
and remove
four
front panel retaining screws.
4.
Pull the
front panel
'
straight
forward
to
remove
it.
4.2
CALIBRATION INSTRUCTIONS
This paragraph provides
complete
sequential calibration
instructions for this
instrument.
The
instructions are
4-1
11/70