PIPER AIRCRAFT, INC.
PA-28-161, WARRIOR III
MAINTENANCE MANUAL
2E7
24-30-00
PAGE 15
Nov 30/06
CHART 4 (Sheet 2 of 3)
TROUBLESHOOTING STANDBY ALTERNATOR REGULATOR (BC203-2D)
Trouble Cause Remedy
6. Move to the engine compartment. Without disconnecting the field connector, measure the field voltage
on the alternator. Use a thin probe or small gage wire wrapped around the probe to reach through the
connector body and measure the voltage on the male blade coming out of the alternator. It should
measure within 0.5 volts of the measurement on Terminal 5 of the regulator. A lack of voltage may
indicate an open circuit between Terminal 5 of the regulator and the field terminal. If an open field circuit
is suspected, the switches may be turned off, the alternator field connector removed, and a resistance
measurement made between the connector and Terminal 5 of the regulator. Look for near 0 Ohms.
Typically the field resistance of the alternator will be between 3 and 10 Ohms from the male field
terminal blade to alternator case.
A. Field terminal voltage:__________volts.
B. Alternator field resistance:__________Ohms.
7. With the switches on, check the voltage between the alternator output post (or B lead) and ground. It
should be battery voltage. If not, check the wiring between the alternator B lead and the battery positive
(+) terminal. Look for loose or contaminated connections, broken wires, or an open breaker or fuse.
Alternator B lead voltage:____________volts.
8. If all of the voltages in the first 6 steps are close to the value specified, the charging system should be
operative. If not, check for a broken or loose alternator belt or, if the alternator is spline driven, check that
the spline drive shear coupling is not sheared. Note that on spline drive alternators the engine speed
must be at or above run-up RPM before checking for useable output.
NOTE: During the following tests, if the annunciator is always ON or always OFF, check the annunciator
circuit by removing the wire from terminal 2 of the regulator. The lamp should be OFF with the
wire disconnected and should illuminate if the wire is connected to ground.
If the lamp circuit works properly but the lamp still remains fixed either ON or OFF all the time
with the lamp wire connected to Terminal 2, assume that the lamp driver is bad in the regulator.
Have the regulator repaired or replaced.
9. If the charging system seems to be generating power, but the STBY ALT ON annunciator will not flash
above 20 amps output, check the following:
A. With the Battery and Standby Alternator Master switches ON but the engine not running, check the
voltage between terminals 4 and 7 of the regulator. The voltage should be 10.0, " 0.1 volts. If it is
not within tolerance, remove the wire from Terminal 4 and re-check the voltage. If it is still not within
tolerance the regulator may be bad. If the voltage is now in tolerance, suspect a bad current sensor
or shorted sensor wire.
B. If the voltage originally measured in step A was in tolerance, divide the measurement by 2. This
value should be the voltage measured between terminals 3 and 7 of the regulator. If the voltage
measured is not close to 5.0 Volts, suspect the current sensor in the standby alternator output lead.
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