Keithley 236 Service Manual

SECTION 3
Maintenance
35
HANDLING
AND CLEANING
PRECAUTIONS
When
troubleshooting or otherwise
working inside the
instrument,
care should
be
taken not
to
indiscriminately
touch PC board traces and open wires to
avoid contami
nating them
with
body
oils
or other foreign
matter. Areas
covered by a
shield
within the Model 236/237
have high
impedance devices or
sensitive
circuitry where contami
nation could
cause
degraded performance.
The same
general precautions
apply when replacing
parts
in
these areas.
When unsoldering and soldering
parts, be
careful not to spread the flux around the board
to
adjacent areas.
1 . Using a
squeeze
bottle,
carefully apply clean,
uncon
taminated methanol to the area to be cleaned. Use
sufficient solution
to
thoroughly wet
the circuit
board.
2.
Using
a
small, clean brush, wipe
the area thoroughly
until it
is
free
of
flux
or
contaminants. In
some cases,
it may be
heipful
to tut the board at
an angle and
brush
contaminants away
from
the
affected area, al
lowing contaminated residue and methanol to run
off
the
board.
3, Wash
the area
again with fresh, clean methanol, al
lowing it
to dram, flushing contaminants off the
board.
4,
Once the area is thoroughly cleaned,
it
should
be
dried
with
pressurized dry clean air or nitrogen.
Do
not
use compressed air
from an ordinary air com
pressor, as oil particles in the air could
contaminate
the
circuit board.
5, After cleaning or parts replacement,
check to see that
any components connected
to
the
Teflon® insula
tors arc not physically
touching the board or
adja
cent parts.
3.6
DISASSEMBLY INSTRUCTIONS
If
it is necessary
to
troubleshoot the instrument
or to re
place
a
component,
use
the
following disassembly proce
dure.
Disassembly should
be
done
in the
order
that
it is
presented since many
steps depend on a previously per-
formed procedure. Procedures pertaining
to
the
Model
237 should
be
ignored if servicing
a
Model
236. Refer
to
Figures
3-2
through
3-6.
NOTE
Connector designations
on the illustrations
use either a “P“
or
“J“
prefix. A “P“
indicates
that the connector
is
a
plug type,
while
“J“
in-
dicates that
it is
a
receptacle.
For example, P10
is a
plug
connector
that
mates
to
receptacle
J10.
WARNING
Disconnect the line cord and any
test leads
from the instrument, and wait at
least three
minutes to
allow high voltage
capacitors to
discharge before
beginning
disassembly.
1 . Remove the top cover as
follows:
A. The top
cover is secured to the
chassis
by
six
screws.
Four arc located at the top
of the instru
ment and two
are located at
the rear. Remove
those six screws.
B. Bilde the
top
cover
towards the
rear of the instru
ment until it separates
completely
from
the
chas
sis,
2.
Remove the bottom cover as
follows:
A If installed
remove the four
plastic feet
located
on the bottom
cover Each foot is secured
with
a
single screw.
CAUTION
To
prevent
damage to
unit or internal
circuit
boards, use #6-32
x
1/4“
bug Phillips
pan
head
screws provided in kit to
secure bottom
cover after removal of feet.
B. The bottom cover is
secured
to
the
chassis
by
two
screws located at
the rear of the
instrument. Re-
move
those
two
screws.
C,
Slide the bottom
cover towards
the rear until
it
completely separates
from the
chassis.
CAUTION
When reinstalling the bottom
cover, use the
proper screws
to
install the
four feet.
Screws
that arc too long
will
cause
damage to
the in-
ternal
circuit boards. The front feet
are
se
cured
by
#6-32 x
5/8“
screws,
and the
rear feet
are secured
by
#6-32 x 1/2“
screws.
If leaving the feet
off in order to install
the
instrument in a
rack,
do
not use the
original
screws
to
secure the bottom
cover.
Instead,
use
the four short screws
(#6-32
x
114“)
sup
plied with the rack mount kit.
3-4

Keithley 236 Specifications

General

Brand	Keithley
Model	236
Category	Measuring Instruments
Language	English