Keithley 2002 Repair Manual

Troubleshooting
2-52
2.11.9 A/D converter ground multiplexer tests
Test 302.1 — Signal zero to ADGND
Type
Pass/Fail
Fault message Signal zero to ADGND
Description 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. To ensure stability of the circuit, the X1 gain is achieved by closing U227
pins 2 to 3 with /X1 low. R274 is in the feedback path of U226. Pin 3 of U226 is also pulled to
common through U222 pin 4 and R259.
Drawing reference Analog Board; 2002-100
Components U226, U227, U242, U253 and associated components.
Bit patterns
Test 302.2 — REFLO to ADGND
Type
Pass/Fail
Fault message REFLO to ADGND
Description 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. To ensure stability of the circuit, X1 gain is
achieved by closing U227 pins 2 to 3 with /X1 low. R274 is in the feedback path of U226, and
pin 3 of U226 is also pulled to common through U222 pin 4 and R259.
Drawing reference Analog Board; 2002-100
Components U222, U226, U242, U253 and associated components.
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—U432—
10000000
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
—U809—
11100111
—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