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Troubleshooting
2-49
2.11.7
A/D multiplexer tests
Test 300.1 — A/D MUX 7V reference, X1 A/D MUX gain
Type
Pass/Fail
Fault message
A/D MUX 7V ref., x1 gain
Description
The 7V reference REFHI generated by U219 and associated circuitry is connected to buffer
U255 with output REFBUF. REFBUF is switched through R263 and U222 pin 5 to pin 3 of
U226. The X1 gain is achieved by closing U227 pins 2 to 3 with /X1 low. R274 is in the feedback
path of U226. The typical reference voltage is actually 7.2V.
Components
U219, U226, U227 and associated circuitry.
Drawing reference
Analog Board; 2002-100
Bit patterns
Test 300.2 — A/D MUX 1.75V reference, X5 A/D MUX gain
Type
Pass/Fail
Fault message
A/D MUX 1.75V ref., x5 gain
Description
The 7V reference REFHI generated by U219 and associated circuitry is connected to buffer
U254. The output of U254 is connected to U230. The 7V reference is switched at 600Hz through
U230. U235 and buffer U241, along with the 25% duty cycle of the 600Hz clock signal, gener-
ates the 1.75V reference (2VREF). 2VREF is switched through R260 and U222 pin 6 to U226.
U226 is set up for X5 gain through U227 pin 10 to 11 with /X5 pin 9 low. R285 provides the
feedback for U226 X5 gain. REFLO is switched through R310 and U242 pins 7 to 6, through
R311, and to pin 3 of U253. U253 is the buffer for ADGND. ADGND buffer with REFLO signal
is connected to the bottom of the parallel combination of R285 and R286. A/D_IN will be the
difference voltage of 2VREF and REFLO (ADGND).
Drawing reference
Analog Board; 2002-100
Components
U219, U226, U235, U241, U254, and associated components.
Bit pattern*
Register
—U400—
01111011
—U811—
00001101
—U224—
00010111
—U432—
10000000
—U810—
00000011
—U206—
01110000
—U203—
10001110
—U411—
11111011
—U809—
11100111
—U207—
00110111
—U221—
11101001
—U406—
00000100
AD_STB
MUX_STB
R1_STB
R2_STB
*Bits associated with register IC terminals as follows:
Q
Q
Q
Q
Q
Q
Q
Q
87654321
87654321
87654321
87654321
IC pins: Q8=11, Q7=12, Q6=13, Q5=14, Q4=7, Q3=6, Q2=5, Q1=4.