Troubleshooting
2-63
2.11.14 100:1 input divider test
Test 307.1 — /100 input divider
Type
Pass/Fail
Fault message
/100 input divider
Description
The 7.2 mA ohms source is switched in with the /OHMA line at U223. U232 pin 2 to 3 connects
REFBUF to U233 pin 3. 7.2V appears across R270. (For a more detailed description of the ohms
source setup, see test 304.1.) In this test, a 10M
Ω
path is provided for current to flow outside of
the ohms source; however a 7.2 mA current through 10M
Ω
would produce a high voltage in ex-
cess of the open circuit ohms clamp. The majority of current flow is downward through the par-
allel path of Q211 and Q212, through CR213, VR204, and Q214 to common. The voltage drop
across the combination of VR204 and Q214 is sensed by the path that routes through Q213,
R322, CR217, K201,R334 and R342. This point is the HI input terminal to the DMM. The
10M
Ω
value described above is the series/parallel combination of R335, R339, R341, and R346.
The 6V open-circuit ohms voltage is divided by 100 and is sensed through Q242 to BUFFIN,
through the input buffer then to A/D_IN. The A/D MUX is configured for X50 gain.
Drawing reference
Analog Board; 2002-100
Components
U223, U232, U233, and associated components.
Bit patterns
Bit pattern* Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—U432—
10000000
—U810—
00000011
—U206—
11000000
—U203—
10001110
—U411—
11111011
—U809—
11100111
—U207—
00001111
—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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