Maintenance
Troubleshooting
4
4-25
Table 4-6. Troubleshooting Guide (cont)
Test and Symptom Possible Cause/Suggestions
Resistance Test (cont)
Low range readings correct,
high range readings off
Q3 and Q4 leak-check by seeing if
MΩ reads OL with open input. Main
pcb contaminated - clean carefully
and check performance.
Current Test
Constant reading of 0.00 Check fuses F1 and F2 with fuse
check procedure in Chapter 2-4.
Fuses F1 and F2 good, but
current readings off
Switches and resistors in current
shunt.
High crest-factor ac current
readings off
U1
Continuity Test
No response Select switch decoding self-test
check for proper function decoding
and also confirm that the continuity
comparator responds. R31, S1A
No tone Q6, R4, LS1. Check U3-1 (tone
output) with scope for 2.667 kHz
signal.
Diode Test
No readings or very low
readings
CR1 (diode test source). To check
CR1, select diode test, connect an
external 1 kΩ resistor across the
inputs and measure the voltage
across the resistor should be
approximately 1V (±10%).
BT Indicator
BT indicator not displayed
when battery voltage is
less that 5.6V
U3, Z4-U3 compares voltage at pin
18 (BT1) with voltage at pin 10
(COM-analog common voltage). BT
turns on if U3-18 voltage is greater
than common. turns off if it is less
(±50 mV)
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