Keithley 2002 Repair Manual

Troubleshooting
2-25
Test 201.1 — Test cal zero
Type
Pass/Fail
Fault message
None
Description
U222 is set up to switch common through R259 and S1 pin 4 input to the A/D buffer U226. U226
is set up for X1 gain through U227 pin 2 to 3 with /X1 pin 1 low. Also, common is switched
through R312 and U242 pins 2 to 3, through R311 and to pin 3 of U253. U253 is the buffer for
ADGND. ADGND is routed to A/D_IN through the parallel combination of R285 and R286.
Common is the input to A/D_IN. Zero reading is acquired and stored for Testcal.
This test is performed by measuring for 0V at A/D_IN.
Drawing reference
Analog Board; 2002-100
Components Switching paths for signals and A/D converter.
Bit patterns
Test 201.2 — 7 Volt reference
Type
Pass/Fail
Fault message Cannot measure 7V at A/D
Description The 7V reference REFHI generated by U219 and associated circuitry is connected to buffer
U255 to generate REFBUF signal. REFBUF is switched through R263 and U222 pin 5 to U226.
U226 is set up for X1 gain through U227 pin 2 to 3 with /X1 pin 1 low. R274 is the feedback
path of U226. REFLO is switched through R310 and U242 pins 7 to 6, through R311, and to pin
3 of U253. U253 is the buffer for ADGND. ADGND buffer with REFLO signal is connected to
the bottom of the parallel combination of R285 and R286. A/D_IN will be the difference voltage
of REFHI (REFBUF) and REFLO (ADGND). The A/D is triggered and the REFHI reading in
counts is acquired and stored for Testcal. REFHI counts are compared to a by design value of
counts.
Drawing reference Analog Board; 2002-100
Components Reference circuit, A/D converter, and the switching paths for the signals.
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—U432—
10000000
—U810—
00010111
—U206—
01110000
—U203—
10001110
—U411—
11111011
—U809—
01101111
—U207—
00001111
—U221—
11101001
—U406—
00000100
AD_STB
MUX_STB
R1_STB
R2_STB
*Bits associated with register IC terminals as follows:
QQQQQQQQ
87654321 87654321 87654321 87654321
IC pins: Q8=11, Q7=12, Q6=13, Q5=14, Q4=7, Q3=6, Q2=5, Q1=4.

Keithley 2002 Specifications

General

Brand	Keithley
Model	2002
Category	Multimeter
Language	English