Piper Comanche PA-24 Service Manual page 669

PIPER COMANCHE SERVICE MANUAL
tator. brushes ... eI iDtemal Corusec:tionl. SticltiDC brush ... a elirty or summy commutator (Reier to
paralf1lpb 9-18). or poor corusectioas .. ay preveat the ..... erator lrom procluciDC any output. Thrown
solder
OD
tb.e cover band indicates that the IHerator ha. been overloaded (aUowed to produce
e:lcessive output) ~
it
baa overheated. aad melted. the solder at the commutator ria.r bars. The
soleler has been throWD out: olten. this leaels to
aD
""en circuit anel burned commutator bars. If the
brushes are satisfactorily seated and are makiDI_lood COIItact with the commutator. IUld the cause
of trouble is not apparent. use a set of test points aad a test lamp as follows to locate tbe trouble
(lelels .. ust be elisconnectecl lrom pnerator termiDals '.
b. Raise the &fOuacled brusb lrom the commutator anel iDsulate witb • piece 01 carelboarel.
Check lor croUDeIs with test POUlts Irom the pIIerator .. aiD brush to the generator Irame. If the
lamp lichts. it iaclicates that the pIIerator is iDtemally &fOUDeled. Location 01 the croUDei can be
10UDd by raiainc anel lDsulating all !xu.hes from the commutator anel checlting the brusb holders.
armaNre, commutator and field separately. Repair or replace defective parts as required (Refer
to paragraph 9-16).
NOTE
If • grOUDeled fie lei is 10UDei. check the ",gulator contact pOints.
since a grounded field may have permitted an excessive field cur·
rHt which will have burned the regu,lator contact points, Bwned
",,,,Iator points shoulel be cleaaecl or "'placed as required.
" II the generator is not &fOunded. cbeck tbe fie lei for an opea circuit with a test lamp. The
lamp should light wben one test point is placed on tbe lielel terminal or &fOuneled field lead and
the other is placed on tbe brush holder to which the lielel is conaected.
1£
it does not light. the
circwt is open. If the open is due to a broken lead or bad connection, it can be repaired, but if
the open is inside one of tbe field coils, it must be replaced.
d. If the lield is not opea. check lor a sbort circuit in the field by connecting a battery 01 tbe
specified voltace and an ammeter in series with the field circuit. Proceed with care, since a
shorted field may draw excessive current wtiich milbt dam ale the ammeter. If the field is not
within spec1fication. new field coils will be required (Reier to paragraph
~16).
NOTE
If a shorted field is found. check the reculator contact pOInts, since
a sborted field may have permitted excessive field current which
would have caused the regulator contact points to bum. Clean or
replace points as required.
e. If the uouble has not yet been located. check the armature for open and short ClrcU.LtS.
Open
circuits in the armature are t.lSually obvious, since the open circUited commutator bars wIll
arc every time they pass IlI1der the generater brushes so that they will soon become burned. If the
bars are not too badly bumed and the open circuit can be repaired. the armature can usually be
saved. In additLOn to repa.1tinl the armature, generator output must be brought down to speci£l-
cations to prevent overloading by readjustment of the regulator.
f. Short circuits ic the armature are located by use ot a growler. The armature is placed
In
the growler and slowly rotated (while a [hln strip of steel such as a hacksaw blade is held above
3 An
ELECTRICAL SYSTEM
ISSUED: 8/1a172