Cessna 177 SERIES Service Manual page 268

16-39A. TROUBLE SHOOTING THE ALTERNATOR SYSTEM (BEGINNING WITH 1978 MODELS) (CONT.)
b. ENGINE RUNNING (Cont.)
TROUBLE PROBABLE CAUSE REMEDY
ALTERNATOR CIRCUIT
Defective circuit breaker. Replace circuit breaker.
BREAKER OPENS WHEN
BATTERY AND ALTER-
NATOR SWITCHES ARE
TURNED ON. OVER-
VOLTAGE LIGHT DOES
NOT COME ON.
ALTERNATOR REGULATOR Shorted field in alternator.
Check resistance from "F"
CIRCUIT BREAKER OPENS terminal of alternator to
WHEN BATTERY AND
alternator case, if resistance
ALTERNATOR SWITCHES is less than 5 ohms repair/
ARE TURNED ON. OVER-
replace.
VOLTAGE LIGHT DOES
NOT COME ON.
CAUTION
This malfunction frequently causes a shorted regulator which
will result in an over-voltage condition when system is again
operated.
ALTERNATOR MAKES Shorted diode in alternator. Turn off Battery Switch and
ABNORMAL WHINING remove "B" Lead from
NOISE alternator. Check reisitance
from "B" terminal of alter-
nator to alternator case. Re-
verse leads and check again.
Resistance reading may show
continuity in one direction but
should show an infinite reading
in the other direction. If an
infinite reading is not obtained
in at least one direction, repair
or replace alternator.
OVER-VOLTAGE LIGHT DOES Shorted regulator Replace regulator
NOT GO OUT WHEN ALTER-
NATOR AND BATTERY
SWITCHES ARE TURNED ON. Defective over-voltage
Replace sensor.
sensor.
AFTER ENGINE START Regulator faulty or high With engine not running turn
WITH ALL ELECTRICAL
resistance in field circuit. off all electrical loads and
EQUIPMENT TURNED OFF turn on battery and alternator
CHARGE RATE DOES NOT
switches. Measure bue voltage
TAPER OFF IN 1-3 MINUTES to ground. then measure voltage
from terminal of alternator to
ground. If there is more than
2 volts difference check field
circuit wiring shown on alter-
nator system wiring diagram in
Section 20. Clean all contacts.
Replace components until there
is less than 2 volts difference
between bus voltage and field
NOTE voltage.
Also refer to battery power system trouble shooting chart.
Change 7 16-12A