Piper PA-24 Comanche Service Manual page 539

PIPER COMANCHE SERVICE MANUAL
tater, brushes and intemal connections. SUclc.iD1 brah.. , a dirty or cummy commutator (Refer to
paralraph 9-18), or poor connections may prevent the poerator from producinl any output. Thrown
solder on the cover band indicates that the leaenator h.1 been overloaded (aUowed to produce
excessive output)
'10
it hu overheated IDd lDelted the solder at the comlillUator riur bars. The
solder has b"n thrown out: often, thil leads to an open circuit and bumed cOlDllnltat!3r ban. 1£ the
brushes are satisfactorily se.ted and
ant
lIlakiallood contact .ith the comlDutator. and the caule
of trouble is not apparent. use a let of tnt poiDts aad a tnt l....p as foUows to locate the trouble
(leads mUlt be dilconnected froID pnerator temina1ll).
b. Raile the pounded brush froID the l;:OCDlDut.tor"lIIld insulate .ith • piece of cardboard.
Check for arounds with test points from the p"erator
maill
brusb to the lenerator frame. 1£ the
lamp lichts, it indicates that the Ifterator is internally pounded. Location of the IfOllftd can be
found by raisiDllDd insulatinl .U brusbes
froca
the COIIIlDutator and cbecltinl the brush holders,
armarote, COlDmutator and field separately. Repair or replace defective part. as required (Refer
to paralraph 9-16).
MOT!
If • arounded field is found. check the replator contact points,
since a lI'ounded field may have permitted
lift
esc"sive field cur-
rent which will bave burned the replator coatact points. Bumed
regulator poiats sbould be cleaned or replaced u required.
e. If the generator is not Founded. check the field for
1ft
open circuit with a test lamp. The
lamp should Hlht when one test point is placed on the field tenDiDal or arouaded field lead and
the other is placed on the brush holder to which the field i. connected. If it does not lilht, the
Circuit is open. If the open is due to • brokell lead or bad connection. it can be repaired. but if
the open is inside one of the field coils. it must be replaced.
d. If the field is not open. check for a short circuit iD the field
by
connectlna a battery of the
speCified voltage and an ammeter in series with the field circuit. Proceed with care, since a
shorted field may draw excessive current wltich !Dilht d_ace the lIIIImeter. If the field is not
within specification, new field coila will be required (Refer to paraaraph 9-16).
MOT!
If a shorted field is found, check the reculator contact points, since
a shorted field may have penDitted exces.ive field current which
would have caused the reauJ.ator contact points to bum. Clean or
replace points as required.
e. If the trouble has not yet been located. check the armature for open and short circuits.
Open dreuits in the armature are usually obvious, since the open circuited commutator bars will
arc every time they pass uftder the leneratcr bru.h•• so that they
will soon become bumed. If the
bars are not too badly bumed and the open circuit can
be
repaired, the armature can usually be
saved. In addition to repairine the armature. lenerator output mUlt be brou&ht down to specifi-
cations to prevent overlo.dine by readjustment of the replator.
£. Short circuits in the armature are located by use of a Itowler. The armatute is placed in
the irowler and slowly rotated (while a thin Strip of steel such u a hacksaw blade is held above
ELECTRICAL SYSTEM
ISSUED: 8/18/72
3 A17
•
•
•