A/D Converter Ground Multiplexer Tests - Keithley 2002 Repair Manual

Troubleshooting
2.11.9

A/D converter ground multiplexer tests

Test 302.1 — Signal zero to ADGND
Type
Fault message
Description
Drawing reference
Components
Bit patterns
Test 302.2 — REFLO to ADGND
Type
Fault message
Description
Drawing reference
Components
2-52
Pass/Fail
Signal zero to ADGND
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.
Analog Board; 2002-100
U226, U227, U242, U253 and associated components.
—U811—
00001101
—U224—
00010111
—U400— —U432—
01111011 10000000
*Bits associated with register IC terminals as follows:
Q Q Q Q
87654321 87654321
IC pins: Q8=11, Q7=12, Q6=13, Q5=14, Q4=7, Q3=6, Q2=5, Q1=4.
Pass/Fail
REFLO to ADGND
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.
Analog Board; 2002-100
U222, U226, U242, U253 and associated components.
Bit pattern*
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Register
—U809— AD_STB
11100111
—U207— MUX_STB
00001111
—U221— R1_STB
11101001
—U406— R2_STB
00000100