Keithley 2002 Repair Manual

Troubleshooting
2-102
2.11.26 Amps/low ohms tests
Test 500.1 — 96µA ohms/200µA DCA range
Type
Pass/Fail
Fault message 96µA ohms/200µA DCA range
Description The 96µA ohms source is switched in using the /OHMC control line at U223 and U220. U232
pin 2 to 3 connects REFBUF to U233 pin 3. The 96µA current divides through Q211 and Q212,
then flows through Q213, R322, CR217, K201,R334 and R342. This point is the HI input ter-
minal to the DMM. The HI to AMPS jumper routes the current to the AMPS line through the
200µA switch (U234 pin 7 to 6), through R295, R319, and R362 to common. 96µA through
1000Ω applies 0.096V to U225 pin 3. U225 is configured for unity gain so the same voltage is
at DCA. DCA is switched through U222 to the A/D MUX U226, and the gain is X1.
NOTE: INPUT HI and AMPS must be externally jumpered together to run this test.
Drawing reference Analog Board; 2002-100
Components U220, U222, U223, U225, U226, U232, U233, and associated components.
Bit patterns
Test 500.2 — 960µA ohms/2mA DCA range
Type Pass/Fail
Fault message 960µA ohms/2mA DCA range
Description The 960µA ohms source is switched in using the /OHMB control line at U223 and U220. U232
pin 2 to 3 connects the REFBUF to U233 pin 3. The 960µA current divides between Q211 and
Q212, then flows through Q213, R322, CR217, K201, R334 and R342. This point is the HI input
terminal to the DMM. The HI to AMPS jumper routes the current to the AMPS line through the
2mA switch (U234 pin 11 to 10), through part of R295, R319, and R362 to common. 960mA
through 100Ω generates 0.096V at U225 pin 3. U225 is configured for unity gain so the same
voltage is at DCA. DCA is switched through U222 to the A/D MUX U226, and the gain is X1.
NOTE: AMPS and INPUT HI must be externally jumpered to run this test.
Drawing reference Analog Board; 2002-100
Components U220, U222, U223, U225, U226, U232, U233,and associated components.
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—U432—
10000000
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
—U809—
11100111
—U207—
10101111
—U221—
11010111
—U406—
00000100
AD_STB
MUX_STB
R1_STB
R2_STB
*Bits associated with register IC terminals as follows:
QQQQQQQQ
87654321 87654321 87654321 87654321
IC pins: Q8=11, Q7=12, Q6=13, Q5=14, Q4=7, Q3=6, Q2=5, Q1=4.

Keithley 2002 Specifications

General

Brand	Keithley
Model	2002
Category	Multimeter
Language	English