Troubleshooting
2-104
Test 500.4 — 20mA DCA range
Type
Pass/Fail
Fault message 20mA DCA range
Description The 7.2mA ohms source is switched in using the /OHMA control 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
terminal to the DMM. The HI to AMPS jumper routes the current to the AMPS line through the
20mA range (Q217 on), through part of R295, R319, and R362 to common. 7.2mA through 10Ω
generates 0.072V at U225 pin 3. U225 is at 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 to run this test.
Drawing reference Analog Board; 2002-100
Components U220, U222, U223, U225, U226, U232, U233, and associated components.
Bit patterns
Test 500.5 — Baseline reading for tests 500.6 and 500.7
Type Circuit Exercise
Fault message None
Description This test uses the same ohms source configuration as above. All amps range switches are open.
Due to the small signals to be measured for tests 500.6.and 500.7, this test takes a baseline read-
ing of any offsets and leakages and subtracts this reading from the readings of tests 500.6 and
500.7. A/D MUX gain is X50.
NOTE: INPUT HI and AMPS must be externally jumpered to run this test.
Drawing reference Analog Board; 2002-100
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00111111
—U432—
10000000
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
—U809—
11100111
—U207—
10101111
—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.
To Next Page
Loading...
Need help?
General
