Wavetek 142 - Maintenance; Access Instructions; Calibration Instructions

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