Range Multiplexer Tests - Keithley 2002 Repair Manual

Troubleshooting
2.11.12 20V range multiplexer tests
Test 305.1 — 20V range multiplexer REFHI
Type
Fault message
Description
Drawing reference
Components
Bit patterns
2-58
Pass/Fail
20V range MUX REFHI
Q201 is turned on, allowing 7.2V REFHI to be applied to the R240 divider. Q203 is always on
because its gate and source are tied together by R241. Since R240 divides by 2, 3.6V appears at
U217 pin 3. Because U217 is a unity-gain buffer, 3.6V 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
Q201, 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.
Bit pattern*
—U810—
00000011
—U206—
01110010
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Register
—U809— AD_STB
11100111
—U207— MUX_STB
01110111
—U221— R1_STB
11101001
—U406— R2_STB
00000100