Keithley 236 Service Manual

SECTION 3
Maintenance
into the instrument
case
while removing the filter
element,
2.
Position the
instrument such that you are facing
the
rear panel. The cooling fan is internally mounted
to
the righthand
end of the rear paneL The filter
as‘
sembly is mounted
to the rear panel in front of the
fan
intake
vents.
3,
Remove the
two
screws that
secure the vented
shroud of the filter
assembly to
the rear paneL The
filter assembly will swing
away from the rear
panel
allowing the
filter element
to be
removed.
4, To clean the
ifiter element, blow out the dust and dirt
with pressurized air
or nitrogen.
5,
Reinstall the
filter assembly onto the rear panel. The
two
hinges of the
filter assembly shroud fit into the
rear panel
vents. Make sure
the filter element covers
all
the rear
panel intake
vents.
NOTE
If the fan filter on
your
unit
is installed inside
the
instrument
case,
you
will
have
to remove
the
top
and
bottom covers in order
to
gain
ac
cess to the filter element
(see
Disassembly,
paragraph
3.6).
The filter
can
be
mounted
to
the outside of the rear panel
by ordering the
shroud (Keithley
p/n
236-332).
3,4
BAERY
REPLACEMENT
When line power
to the Model
236/237 is turned off, the
lithium battery on
the digital
board provides backup
power
to
the
memory in
which user
programmed setup
conditions
and
sweep
data
are
stored. The battery has
enough capacity
to maintain data for one
year
of
continu
ous power off,
or
two
years
if the Mode1236/237 is on for
12
hours every
day. The battery
by
itself
has
a
shelf life of
eight
years. Although
the Model
236/237
wffl operate
without
a
battery, it will
not retain any
setup conditions
or
sweep data
when
turned off.
The instrument will
power up
to
the
factory default
conditions.
The battery
may
be
replaced
with any 2450
lithium
coin
cell.
lt can also
be
ordered from Keithley
(part number
BA-44).
Replacement
ofthe lithium battery
is normally a safe pro-
cedure
as
long as these safety
precautions are followed.
WARNING
The precautions
below
must
be
followed to
avoid
possible
personal
injury.
1. Do not short
the battery terminals
together.
2.
Do not incinerate
or otherwise expose to
excessive
heat
(>60°C).
3,
Keep
lithium batteries away
from all liquids.
4. Do not recharge
lithium batteries.
5,
Observe proper
polarity when
inserting battery into
holder.
Replace the battery as
follows:
1 . Turn off the power, disconnect
the line cord, and
re
move
all
test
leads.
2.
After allowing at
least three
minutes for internal ca
pacitors
to
discharge,
remove
the
top
cover (see
paragraph
3.6).
3,
The battery is on the
digitalboard
(see
Figure
3-2
for
location).
Pry the battery
out of its holder
using
a
non-metallic tool.
WARNING
Do not use a
metal tool to pry out
the battery
as you
could short the
terminals.
4. Install the new battery,
taking care to
observe proper
polarity
as
stamped on the
battery holder. The
plus
(+)
terminal of the battery
faces up.
5,
Reinstall
the top
cover.
3-2

Keithley 236 Specifications

General

Brand	Keithley
Model	236
Category	Measuring Instruments
Language	English