Keithley 2002 Repair Manual page 66

Bit patterns
Test 302.3 — Ohms LO to ADGND
Type
Fault message
Description
Drawing reference
Components
Bit patterns
—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
Ohms LO to ADGND
Common is switched through the parallel combination of R313 and R314 and U242 pins 10 to
11, through R311 and to pin 3 of U253. U253 is the buffer for ADGND. ADGND buffer with
Ohms LO 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. Pin 3 of U226 is also pulled to common through U222
pin 4 and R259.
Analog Board; 2002-100
U222, 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.
Bit pattern*
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Bit pattern*
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Troubleshooting
Register
—U809— AD_STB
11100111
—U207— MUX_STB
00010111
—U221— R1_STB
11101001
—U406— R2_STB
00000100
Register
—U809— AD_STB
11100111
—U207— MUX_STB
00011011
—U221— R1_STB
11101001
—U406— R2_STB
00000100
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