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236
Keithley 236 Service Manual
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SECTION
3
Maintenance
Volts
Rangmg
Table
35
hsts
the
switches
that
are
closed
for
each
of
the
available
voltage
ranges.
This
table
applies
to
both
source
and
measure
voltage
ranges.
Table
35,
Analog
Switching;
Volts
Ranging
K15
and
K5
wffl
dose
whenever
the
instrument
is
placed
in
standby.
Table
34,
Analog
Switching
Sensing
Relays
Range
Closed
FET
Switches
Closed
L1V
K4,
K6,
K7
Q24,
Q33,
Q35
liv
K4,
K6,
K7
Q24
110V
K7
—
1100V
—
—
Feedback
As
listed
in
Table
3-6,
analog
switches
U48
and
U49
are
used
for
feedback
switching.
Each
of
these
two
devices
has
four
individual
switches
and
are
identi
fied
by
their
circuit
schematic
pin
numbers.
The
table
lists
the
states
of
these
switches
for
standby
and
operate
con
ditions
while
programmed
to
source
current
and
voltage.
Sensing
—
As
listed
in
Table
37,
three
relays
are
used
to
select
local
or
remote
sensing.
Note
that
when
the
instru
ment
is
programmed
for
remote
sensing,
the
relay
switches
wffl
default
to
the
local
sensing
states
when
placed
in
standby.
That
is,
relay
K3
will
open,
and
relays
_______
Relays*
Sense
K3
K15
K5
Local
Open
Closed
Closed
Remote
Closed
*Relay
states
with
236/237
in
OPERATE.
In
standby,
relays
go
to
local
sense
states.
Output
—
For
safety,
there
are
two
relays
that
are
used
to
disconnect
OUTPUT
HI
and
SENSE
HI
from
the
rear
panel
output
triax
connectors.
When
the
instrument
is
off,
relays
Kl
and
K2
are
open.
When
turned
on,
these
re
lay
switches
remain
open
until
the
instrument
is
first
placed
in
operate.
These
two
switches
then
remain
closed
while
the
instrument
is
powered
on.
A/D
Multiplexing
—
During
normal
operation,
the
A/D
multiplexer
(Ui)
continuously
applies
a
sequence
of
sig
nals
to
the
input
of
the
A/D
converter.
These
signals
in-
clude
Zero,
Reference
and
Measure
(1
or
V).
Only
one
sig
nal
is
switched
to
the
A/D
input
at
one
time.
The
switch
ing
speed
and
sequence
varies
according
to
how
the
in-
strument
is
programmed
to
operate.
In
the
A/D
test
mode
(see
paragraph
3.8.2)
the
A/D
con
verter
is
locked
up
in
the
desired
A/D
phase.
This
allows
Table
3-6,
Analog
Switching;
Feedback
Switches
Source
1
Measure
V
Source
V
Measure
1
Device
Pins
Standby
Operate
Standby
Operate
U48
6,
7
Closed
Open
Closed
Closed
U49
6,7
Closed
Open
Closed
Closed
U48
2,
3
Closed
Open
Closed
Closed
U49
10,
11
Closed
Open
Closed
Closed
U48
10,
11
Open
Closed
Open
Open
U49
14,
15
Open
Closed
Open
Open
U48
14,
15
Open
Closed
Open
Open
2,
3
=
Closed
3-15
85
87
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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