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Keithley 236 Service Manual
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SECTION
3
31
INTRODUCTION
This
section
contains
information
necessary
to
maintain
and
troubleshoot
the
Model
236/237.
WARNING
Other
than
line
fuse
replacement
and
fan
fi1
ter
cleaning,
the
procedures
included
in
this
section
are
for
use
only
by
qualified
service
personne1
Do
not
perform
these
procedures
unless
qualified
to
do
so.
Troubleshooting
steps
may
expose
you
to
potentially
lethal
voltages
that
could
result
in
injury
or
death
if
normal
safety
precautions
are
not
ob
served.
32
LINE
FUSE
REPLACEMENT
A
rear
panel
fuse
located
adjacent
to
the
line
voltage
switch
(see
Figure
3-1)
protects
the
power
line
input
of
the
Source
Measure
Unit.
If
the
fuse
needs
to
be
replaced
(line
voltage
switch
setting
changed
or
suspected
blown
fuse),
perform
the
following
steps:
WARNING
Make
sure
the
Source
Measure
Unit
is
dis
connected
from
the
power
line
and
other
equipment
before
replacing
the
fuse.
L
With
the
power
off,
place
the
end
of
a
f1atb1ade
screwdriver
into
the
siot
in
the
rear
panel
line
LINE
FUSE
holder.
Push
in
gently
and
rotate
the
fuse
car
ncr
onequarter
turn
counterclockwise.
Release
pressure
on
the
holder
and
its
internal
spring
will
push
the
fuse
and
carrier
out
of
the
hoMer.
2.
Remove
the
fuse
and
replace
it
with
the
type
recom
mended
in
Table
3-1.
CAUTION
Do
not
use
a
fuse
with
a
higher
current
rating
than
specified,
or
instrument
damage
may
occur.
If
the
instrument
repeatedly
blows
fuses,
locate
and
correct
the
cause
of
the
trouble
before
replacing
the
fuse.
See
para
graph
3.8
for
troubleshooting
information.
3,
Install
the
new
fuse
and
the
fuse
carrier
into
the
holder
by
reversing
the
above
procedure.
Table
3-1.
Line
Fuse
Selection
Line
Keithley
Voltage
Fuse
Type
Part
Number
195-250V
1
/2A,
250V,
3AG,
Sb
Blo
FLJ-4
90-125V
1A,
250V,
3AG,
Sb
Blo
FU-1O
LINE
VOLTAGE
LINE
FUSE
SELECTED
SLOWBLOW
Ø
Figure
34.
Line
Voltage
Switch
and
Line
Fuse
3,3
FAN
FILTER
CLEANING
The
Model
236/237
has
an
internal
cooling
fan
to
vent
heat
out
of
the
instrument
case.
The
fan
has
a
filter
to
keep
dirt
and
dust
from
entering
the
instrument
case.
Con
tamination
on
PC
boards
could
result
in
degraded
per-
formance.
The
fan
filter
must
be
Cleaned
periodically
to
maintain
internal
cleanliness
and
proper
ventilation.
Perform
the
following
steps
to
remove
and
clean
the
fan
filter
element:
1.
Turn
off
the
Model
236/237.
The
fan
must
be
off
in
order
to
prevent
dirt
and
dust
from
being
ingested
3-1
72
74
Table of Contents
Table of Contents
21
Performance Verification
27
Introduction
27
Environmental Conditions
27
Initial Cond1Tions
27
Required Test Equtpment
28
Verifications Procedures
28
Equipment Characterization
30
Table 1-3 Model 263 I-Source Characteristics
31
Common Mode Verification
32
Figure 1-2 Setup for Common Mode Verification
33
Voltage Source Verification
34
Figure 1-3 Setup for Voltage Source Ranges Verification
35
Voltage Measure Verification
35
Figure 1-4. Setupfor Voltagemeasure Ranges Verification
36
Table 1-5 Voltage Measure Verification
37
Remote Sense Verification
37
Figure 1-5 Setup for Remote Sense Verification
38
Low Current (Ina to Loma) Measure Ranges Verification
38
Low Current (Ina to Loma) Source Ranges Verification
43
Looma Measure Range Verification
44
Figure 1-8 Setup for Looma Measure Range Verification
45
Looma Source Range Verification
46
Calibration
49
Introduction
49
Recommended Calibration Equipment
49
Environmental Conditions
50
Warmup Period
50
Cal Lock
50
Calibration Procedures
50
Equipment Characterization
51
Figure 2-2 Setup for Equipment Characterization
52
Table 2-3 Model 263 I-Source Characterization
53
Voltage Calibration
54
Figure 2-3 Setup for Volts Calibration
55
Looma Range Calibration
57
Low Current Ranges Calibration (Ina Loma)
59
Calibration Errors
61
Table 2-4 Calibration Error Messages
62
Calibration Program
64
Table 3-1 Line Fuse Selection
73
Introduction
73
Line Fuse Replacement
73
Fan Filter Cleaning
73
Handling and Cleaning Precautions
76
Disassembly Instructions
76
Figure 3-3 Resonant Converter Board (Model 237)
77
Figure 3-4 Output Board
78
Figure 3-5 Analog Board (Shields Removed)
79
Diagnostics
82
Table 3-2 Recommended Troubleshooting Equipment
82
Special Handling of Static Sensitive Devices
82
Recommended Test Equipment
82
Power Supply Checks
84
Table 3-3 Power Supply Checks
84
Analog Switching
85
Table 3-4 Analog Switching; Current Ranging
85
Table 3-5 Analog Switching; Volts Ranging
86
Table 3-6 Analog Switching; Feedback
86
Digital and Display Checks
87
Table 3-9 Digital Circuitry Checks
88
Table 3-10 Display Circuitry Checks
89
Principles of Operation
90
Introduction
90
Analog Circuitry
91
V/I Control and Readback
91
Output Stage
93
Figure 4-3 Model 236 Output Stage (Simplified Schematic Diagram)
94
Feedback
95
Figure 4-6 Damping Relay Contact Bounce
96
Resonant Converter (Model 237)
97
A/D Converter
97
Table 4-1 Volts Range Relays
97
Digital Circuttry
98
I/O Controller
98
Source/Measure Controller
99
Communications
99
A Display Circuitry
99
Powersupply
100
Introduction
102
Parts Lists
102
Ordering Information
102
Schematic Diagrams and Component Location Drawings
102
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Keithley 236 Specifications
General
Brand
Keithley
Model
236
Category
Measuring Instruments
Language
English
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