Keithley 2002

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Troubleshooting

2-50

Bit patterns

Test 300.3 — A/D MUX 0V reference, X50 A/D MUX gain

Type

Pass/Fail

Fault message A/D MUX 0V ref., x50 gain

Description U222 is set up to switch common through R259 and S1 pin 4 input to the A/D buffer U226. U226

is set up for X50 gain through U227 pin 15 to 14 with /X50 pin 16 low. R286 provides the feed-

back for U226 X50 gain. Also, common is switched through R312 and U242 pins 2 to 3, through

R311 and to pin 3 of U253. U253 is the buffer for ADGND. ADGND is routed to A/D_IN

through the parallel combination of R285 and R286. Common is the input to A/D_IN. Common

is switched through R259 and U222 pin 4 to pin 3 of U226.

Drawing reference Analog Board; 2002-100

Components U222, U226, U227, U253, and associated components.

Bit patterns

Bit pattern* Register

—U400—

01111011

—U811—

00001101

—U224—

00010111

—U432—

10000000

—U810—

00000011

—U206—

10110000

—U203—

10001110

—U411—

11111011

—U809—

11100111

—U207—

01010111

—U221—

11101001

—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.