Absolute Value Circuit X1 Gain Tests - Keithley 2002 Repair Manual

Troubleshooting

2.11.18 Absolute value circuit X1 gain tests

Test 404.1 — Absolute value X1 gain, - full-scale DAC
Type
Fault message
Description
Drawing reference
Components
Bit patterns
Test 404.2 — Absolute value X1 gain, - half-scale DAC
Type
Fault message
Description
Drawing reference
Components
2-72
Pass/Fail
Absolute value gain = 1
DAC U433 and op amp pair U430 are set up to generate -4.36 VDC at PRECOMP+ and tied to
ACF through R491 and U412. ACF is tied to AMP IN through U428, Q422, and the ACV buffer.
AMP IN is tied to the inverting and non-inverting paths of FWR. NETOUT from U417 in the
non-inverting path is monitored by the ZERO CROSSING amp for positive or negative polarity
of the input signal and generates the COMP- signal that is fed to comparator U408. The com-
parator selects the path that the AMP IN signal will follow through the FWR with switches
U410. The minus AMP IN path is through the inverting path R452, U418, U410, Q404, and
U419 to pin 12 of the U414 multiplexer. The output of the multiplexer is tied to the A/D through
buffer U403, ACV/A input to U222, and the A/D buffer in the X1 gain configuration.
Analog Board; 2002-100
U403, U417, U418, U419, U428, U430, U433, and associated components.
—U811—
00001101
—U224—
00010111
—U400— —U432—
01011100 00010111
*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.
Pass/Fail
Absolute value gain = 1
DAC U433 and op amp pair U430 are set up to generate -2.15 VDC at PRECOMP+. This signal
follows the same path as test 404.1.
Analog Board; 2002-100
U403, U414, U417, U418, U419, U428, U430, U433, and associated components.
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
01001101