To Next Page

To Previous Page

Troubleshooting

2-62

Components

U220, U223, U232, and associated components.

Bit patterns

Test 306.3 — High ohms voltage source

Type

Pass/Fail

Fault message

High ohms voltage source

Description

The HIOHMSRC line at pin 7 of U231 is approximately 14.4V. This voltage is generated by the

Ohms Reference U230 switching OHMREFHI onto C227 that is relative to REFBUF. HIOHM-

SRC is then switched through U244 pin 6 to 7, through Q226, through the 100k

Ω

leg of the input

divider, and through Q242 to BUFFIN. The 20V range MUX signal path is now used. Q205 is

turned on so that the signal reaches R204. Q203 is always on because its gate and source are tied

together by R241. 7.2V appears at U217 pin 3. Since U217 is a unity gain buffer, 7.2V also ap-

pears at U222 pin 7. The U222 control lines are conﬁgured to switch the pin 7 input to the U222

output and to the A/D buffer in the X1 conﬁguration.

Drawing reference

Analog Board; 2002-100

Components

U222, U231, U244, and associated components.

Bit patterns

Bit pattern* Register

—U400—

01111011

—U811—

00001101

—U224—

00010111

—U432—

10000000

—U810—

00000011

—U206—

01100000

—U203—

11010110

—U411—

11111011

—U809—

11100111

—U207—

00001111

—U221—

11101001

—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.