Piper PA-24 Comanche Service Manual page 571

PIPER COMANCHE SERVICE MANUAL
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fiGURE 9-27,. TISTING ROTOR
POR GROUNDS
"HEOSTAT
"GUll 9-m. TISTING ROTOR
fOR
SHORTS
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a lead bom one of the rectifiers in that heat siAlc. Thea Nveme the polition of the leads. The
test bulb should hlht in one diNction and not Ucht in tbe other direction. If the test bulb lilhts
in both directions. one or more
of
the Netitia,. iJl that heat sink is ahorted. To pinpoint the de-
fecti ve rectifier. the ,tator lead. must be ciilcollDeeted aDd the above test repeated on each
rectifier. Open rectifiers can only be detected, wben ..inl d.- t.t bwb, by discoMKtinc the
stator leads. The test bulb will fail to liaht in either diJeCtion if the seetifier i. open.
c. Stator: The stator c.n be tested for open or lroudtld wirdine' with a 12-volt test bulh,
described in the rectifier section. or an ohlDllleter. in ta. foUGWinc Ilanner. Separate the stator
from the slip rina end head
j ..
t far enoulh to .ert a fold of rap or blocks of wood. In other
words. insulate the stator frOIl the end head. To
telt
for FOUDdecl windinp. touch one test bulb
or ohllUDeter probe to the stator &ame. If the test bulb Uahts, or the ohmmeter indicates con-
tinuity, the stator is Ifounded. To te.t for open wiftdinp, coo_ct one tut probe to the auxiliary
terminal or the stator windilll center cOn.nection aad touch e.ch of the three stator leads. The
!est bulb must hCht, or the ohmmeter must show contillllity. Due to the low resistance in the
stator windinp. shorted windin.. are .lmoat impc:a.ible to lacate. Ho"ever. shorted stator
win:linp will usually cause the alttlrnator to upowl" or be noisy durina operation and will
usually show some silna of overheatina.
U
aU atber electrical
ebecu
are normal and the al-
ternator fails to supply its rated output, the stator should be replaced to deterllline whether or
not it is the faulty component.
d. Bearinp and S..ls: Whenever the alternator is
overhauled, new beatinas and oilor crease
seals are recommended. even thoulh the bean. . and .eals appear to be in Coed condition. A
faulty seal can cause an alternator to fail within a very ahort period of time.
ELECTRICAL SYSTEM
ISSUED: 8I18nZ
3 Cl