Maintenance
Troubleshooting
5
5-25
Table 5-7. Troubleshooting Guide (cont)
Test and Symptom Possible Cause/Suggestions
Power Supply
VDD (voltage between
TP7 and common)
≠5.2 ±0.12V
U3, Q1, VR1
VDG (voltage between
TP7 and TP8)
≠3.15 ±0.08V
U3, C21, U5
VSS (voltage between
TP2 and common)
≠-5.1 ±0.27V
U4, C21, C23
TP4 ≠1.225 ±0.025V
U3-11 ≠1.000 ±0.0004V
Hint: if you suspect U3 power
supplies are bad, you can drive the
8060A power supplies externally.
Remove battery, µC pcb, and U3.
Apply +5.2V at TP1 - you can then
check the ac converter, diode test
source, VR2, U4, and the power
supply circuitry.
Voltage Test - DC
Gross error (constant
reading of 0.00 or OL)
Perform ratio self-test in dc volts. If
count is good, U3 is good. If count is
way off, suspect U3, C9 R33, R8 Z3,
C16 or C18
Ratio self-test passes,
but constant reading
of 0.00
R1, R2 (fusible resistors - replace
with exact equivalent only). RJ1, RJ2,
RJ3, RJ4 (varstors turn yellow when
shorted), open circuit in front end, bad
component is input divider, U3 pins 6
and 7 shorted. (Hint: check high
impedance dc voltage first, which
bypasses the input divider.) Refer to
Table 4-1 for input divide rations.
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