Keithley 2002 Repair Manual page 73

Troubleshooting
Bit patterns
Test 305.4 — 20V range multiplexer signal
Type
Fault message
Description
Drawing reference
Components
Bit patterns
2-60
—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
20V range MUX signal
The ohms source is in the same configuration as test 304.1 to create 6V at input HI, which is the
HI input terminal to the DMM. This signal is then switched through the Q246, Q245, Q244 path
to BUFFIN. Q205 is turned on so that the signal reaches R240, and Q203 is always on because
its gate and source are tied together by R241. 3V appears at U217 pin 3. Since U217 is a unity-
gain buffer, 3V also appears at R261, and U222 switches pin 7 to pin 3 of U226. X1 gain is
achieved by closing U227 pins 2 to 3 with /X1 low, and R274 is in the feedback path of U226.
Analog Board; 2002-100
Q205, U217, U222, U226, U227, 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—
01110100
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Bit pattern*
—U810—
00000011
—U206—
01111000
—U203—
11110100
—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
Register
—U809— AD_STB
11100111
—U207— MUX_STB
01101111
—U221— R1_STB
01110111
—U406— R2_STB
00000100