Keithley 2002 Repair Manual page 72

Test 305.2 — 20V range multiplexer REFLO
Type
Fault message
Description
Drawing reference
Components
Bit patterns
Test 305.3 — 20V range multiplexer zero
Type
Fault message
Description
Drawing reference
Components
Pass/Fail
20V range MUX REFLO
Q206 is turned on, allowing the 0V REFLO to be applied to the R240 divider. Q203 is always
on because its gate and source are tied together by R241, and 0V appears at U217 pin 3. Since
U217 is a unity-gain buffer, 0V 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
U217, U222, U226, 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
20V range MUX zero
Q202 is turned on, allowing the 0V common to be applied to the R240 divider. Q203 is always
on because its gate and source are tied together by R241. 0V appears at U217 pin 3. Since U217
is a unity gain buffer, 0V 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. R274 is in the feedback path of U226.
Analog Board; 2002-100
Q202, U217, U222, U226, U227, and associated components.
Bit pattern*
—U810—
00000011
—U206—
01110001
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Troubleshooting
Register
—U809— AD_STB
11100111
—U207— MUX_STB
01110111
—U221— R1_STB
11101001
—U406— R2_STB
00000100
2-59