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5.4.1 Voltage Checks
Several voltage checks can be made simply by connecting a
DMM to various A/D converter IC pins. Table 5-2 summarizes
these voltage readings.
TABLE 5-2
VOLTAGE CHECKS
5.4.2 A/D Converter Checks
A/D converter operation can be checked by measuring the input
and reference voltages and then comparing the displayed reading
to a value calculated from these input voltages.
1. Connect a temperature probe to the instrument; make sure
the temperature remains stable while making voltage
measurements.
2. Connect the DMM LO terminal to analog common (pin 32 of
U102).
3. Connect the DMM HI terminal to pin 31 (IN HI) of U102 and
record the reading.
4. Connect the DMM HI terminal to pin 30 (IN LO) of U102
and record the reading.
5. Connect the DMM HI terminal to pin 35 (REF HI) of U102
and record the voltage.
6. Connect the DMM HI terminal to pin 36 (REF LO) and record
the reading
Using the measured values above, calculate the displayed
reading (neglecting the decimal point) as follows:
Display = 1000
(IN HI-IN LO)
(REF HI-REF LO)
If the displayed value does not agree with the calculated value to
within a few digits, the A/D converter is not functioning properly.
REQUIRED
STEP ITEM/COMPONENT CONDITION COMMENTS
1 Connect DMM HI to +V Leave connected for
all voltage checks.
2 Connect DMM LO to >7.2 V dc Battery voltage
U102, pin 26 (-V)
3 Connect DMM LO to 5V ± 1 V dv Digital Common
U102, pin 37 (TEST)
4 Connect DMM LO to 3 V IN LO (COM)
U102, pin 30