Maintenance
Troubleshooting 3
3-17
1. If Vdd - Vss is low, a problem may exist with start-up device Q10. Check Q10 by
momentarily connecting Vss to Vbt-. If both Vss and Vbt- now start up and operate
correctly, check Q10 for an open.
2. Measure the ac voltage between Vdd and Vss. An unstable Vdd regulator can be
caused by an open C14. If the voltage is greater than 10-mV ac, check C14. The dc
level may also be incorrect.
For a final check of U4, remove the battery and supply Vdd = +3.0V, Vdgnd = 0, and Vss
= -3.2V from an external power supply. Measure the voltage at U4 pin 7 (Vps0). If it
does not equal 1.23V ± 0.15V, check R24 and R25 carefully. If Vps0 is still incorrect, U4
is bad.
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