Keithley 2002

Troubleshooting
2-108
Test 501.2 — Amps bootstrap
Type
Pass/Fail
Fault message Amps bootstrap
Description The 7.2mA ohms source is switched in using the /OHMA line at U223 and U220. U232 pin 2
to 3 connects the REFBUF to U233 pin 3. The 7.2mA current divides between 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. All of the amps
range switches are off. All current flows through CR218, and the voltage is clamped at two diode
drops (approximately 1.2V) by CR218. This voltage is fed to U225 pin 3, which is at unity gain
so this voltage is at the AMPBOOT line. AMPBOOT is switched through U222 to the A/D MUX
U226, and the gain is X1.
NOTE: INPUT HI and AMPS 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 patterns
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—U432—
10000000
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
—U809—
11100111
—U207—
11101111
—U221—
01110111
—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.