Keithley 2002 Repair Manual page 95

Troubleshooting
Drawing reference
Bit patterns
Test 406.5 — Sample and hold output (-0.01V)
Type
Fault message
Description
Drawing reference
Bit patterns
2-82
and the output value (SELFTEST OUT) can be compared to check for circuit accuracy in test
phase 406.6.
Analog Board; 2002-100
—U811—
00001101
—U224—
00010111
—U400— —U432—
01011011 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.
Circuit Exercise
None
DAC U433 and op amp pair U430 are set up to generate -0.01 VDC at PRECOMP+ and tied to
ACF through R491 and U412. ACF is buffered to AMP IN through U428, Q422, and ACV buff-
er. AMP IN is tied through U425 to inverting X5 gain U426, R466, and R465. The SELFTEST
signal causes one-shot U402 to output a 5µs low pulse, turning U425 and Q414 ON for 5µs. The
value from inverter U426 is stored on C439 and applied to buffer Q409. SELFTEST OUT is the
value on C439 and the V
GS
The multiplexer output is tied to the A/D through buffer U403, ACV/A input to U222, and the
A/D buffer in X1 gain configuration.
Analog Board; 2002-100
—U811—
00001101
—U224—
00010111
—U400— —U432—
01011101 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—
01110000
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
value of Q409. This signal is applied to multiplexer U414 pin 11.
Bit pattern*
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
Q Q Q Q
87654321 87654321
Register
—U809— AD_STB
11100111
—U207— MUX_STB
11001111
—U221— R1_STB
11101001
—U406— R2_STB
01001111
Register
—U809— AD_STB
11100111
—U207— MUX_STB
11001111
—U221— R1_STB
11101001
—U406— R2_STB
01001101