Troubleshooting
2-107
2.11.27 Amps protection tests
Test 501.1 — Amps protection
Type
Pass/Fail
Fault message Amps protection
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. The 200µA
range switch U234 pin 7 to 6 is closed. 7.2mA through 1000Ω would normally generate a large
voltage at U225 pin 5; however the voltage is clamped at two diode drops (approximately 1.2V)
by CR218. U225 is at unity gain so this 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
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—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.
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