8060A
Instruction Manual
5-28
Table 5-7. Troubleshooting Guide (cont)
Test and Symptom Possible Cause/Suggestions
Frequency Test (cont)
Frequency calibration is good
and signal present at U3-4,
but frequency readings off
Frequency compactor in U3 not
responding. To check comparator,
select switch-decoding self-test and
apply input of 15 mV ac in the 200
mV ac range. Adjust R9 so that the
continuity bar at the top of the display
flashes off and on. If the bar will not
flash, U3 is bad. If the bar flashes, but
frequency readings are still off, U3 or
U5 are bad. Check oscillation of
crystal Y1 by measuring the
frequency at U3-38 with another
frequency counter - should be 40.000
±0.020 kHz.
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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