Maintenance-2445A/2455A Service
REMOVAL AND REPLACEMENT
INSTRUCTIONS
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I
To
avoid electric shock, disconnect the instrument
from the ac power source before removing
or
replac-
ing any component
or
assembly.
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Removal
of
the
cabinet and other external panels
leaves the CRT exposed for possible
damage.
All
procedures
in
these instructions require careful
attention to avoid damage to the CRT which could
cause
it
to implode. An implosion creates high speed
glass fragments.
Wear
protective clothing and use
safety shields
as
required.
See
"WARNING"
in
"CRT
REMOVAL".
The exploded view drawing
in
the "Replaceable
Mechanical Parts• list at the rear of this manual may
be
helpful during the removal
and
reinstallation of individual
components or subassemblies. Circuit board
and
com-
ponent locations are illustrated
in
the "Diagrams• section
of this manual.
Cabinet Removal
Removal
of
the instrument wrap-around cabinet is
accomplished
by
the following steps:
1 . Unplug the power cord from the ac power source.
2.
Unplug the power cord from the rear-panel
connector.
3.
Install the front cover, place the cabinet carrying
handle against the bottom of the cabinet,
and
set the
instrument face down on a flat surface.
4.
Unwrap the power cord
and
remove it.
5.
Remove the four screws
in
the rear feet.
6-24
6.
Remove the two screws from the top-center
and
bottom-eenter of the rear cover.
7.
Lift the rear cover and power cord away from the
instrument, leaving the rear feet attached.
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Dangerous potentials exist
at
several points
throughout this instrument.
If
it is operated with
the
cabinet removed, do not touch exposed connections
or
components. Some transistors may have elevated
case voltages. Disconnect
the
ac power source from
the instrument and verify that the line-rectifier filter
capacitors have discharged before cleaning
the
instrument
or
replacing parts
(see
label on the pri-
mary power
shield).
8.
Slide the cabinet off the instrument.
To reinstall the wrap-around cabinet, perform the
reverse of the preceding instructions. Ensure that the
cabinet fits properly into the
EM
I gasket grooves
in
the
front frame
and
rear panel.
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The
line-rectifier filter capacitors normally retain a
charge for a short period (approximately
15
to 20
seconds) after
the
instrument is turned
off
and
can
remain
charged for a longer period
if
a bleeder-
resistor
or
power-supply problem occurs. Before
beginning any cleaning
or
work on
the
internal cir-
cuitry
of
the oscilloscope, disconnect the ac power
source from
the
instrument and verify that
the
capacitors have discharged to 24 V
or
less.
Mea-
surement is
made
at
the three points indicated on
the plastic primary input shield
at
the
rear
of
the
instrument (after the Top-Cover Plate
is
removed).
If
the capacitors retain charges
of
greater than
24
V
for more than 20 seconds, discharge them using a
1
kfJ,
5-watt resistor connected point~to-point across
the capacitors through the access
holes.
Ensure that
the capacitors are discharged before starting to
troubleshoot.
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