Piper Dakota Maintenance Manual page 215

2. Rectifiers: A diode rectifier tester detects and pinpoints open or shorted rectifiers without
disconnecting stator leads. However, if a tester is not available, test probes and a number 57 bulb,
connected in series with a 12-volt battery, can be used. Touch one test probe to a rectifier heat sink and
other test probe to a lead from one of the rectifiers in that heat sink. Then reverse position of leads.
Test bulb should light in one direction and not light in other direction. If test bulb lights in both
directions, one or more of rectifiers in that heat sink is shorted. To pinpoint defective rectifier, stator
leads must be disconnected and above test repeated on each rectifier. Open rectifiers can only be
detected, when using test bulb, by disconnecting stator leads. Test bulb will fail to light in either
direction if rectifier is open.
3. Stator: Test stator for open or grounded windings with a l2-volt test bulb, as described in rectifier
section, or an ohmmeter, as follows. Separate stator from slip ring end head just far enough to insert a
fold of rags or blocks of wood. Insulate stator from end head. Test for grounded windings by touching
one test bulb or ohmmeter probe to auxiliary terminal or any stator lead, and other test bulb or
ohmmeter probe to stator frame; If test bulb lights, or ohmmeter indicates continuity, stator is
grounded. Test for open windings by connecting one test probe to auxiliary terminal or stator winding
center connection and touch each of the three stator leads. Test bulb must light, or ohmmeter must
show continuity. Due to low resistance in stator windings, shorted windings are almost impossible to
locate. However, shorted stator windings will usually cause alternator to growl or be noisy during
operation and will usually show some signs of overheating. If all other electrical checks are normal
and alternator fails to supply its rated output, replace stator to determine whether or not it is the faulty
component.
4. Bearings and Seals: Whenever alternator is overhauled, new bearings and oil or grease seals are
recommended, even though bearings and seals appear to be in good condition. A faulty seal can cause
alternator to fail within a very short period of time.
ASSEMBLY OF ALTERNATOR
l. Press ball bearing into drive end head using a flat block approximately two inch square so that
pressure is exerted on outer race of the bearing. Install retainer plate. With snap ring and retainer cup
in place on rotor shaft, use a tool that fits over shaft and against inner bearing race, and press until
inner bearing race is against snap ring retainer cup. (Refer to figure 24-35-)
2. Carefully install rectifiers in slip ring end head or rectifier mounting plate by supporting unit and using
special tools illustrated in figure 24-36.
Use an arbor press, do not hammer. Reconnect stator leads to
rectifiers. When soldering these connections, use pliers as a heat
dam on lead between solder joint and rectifier. Too much heat
will damage rectifiers.
3. Reassemble rectifier mounting plate studs and insulators. Make sure they are in correct order. (Refer to
figure 24-37.)
4. After slip ring end head is completely assembled, stator and rectifier leads must be secured to rectifier
mounting plate with epoxy. Make sure stator leads are positioned so that they do not interfere with
rotor.
5. Install slip ring end bearing and oil seal. Make sure lip of oil seal is toward bearing. Stake oil seal in
place. Correct assembly of bearing, seal, inner race, and spacer is shown in figure 24-38.
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
—CAUTION—
1J6
24 - 33 - 00
Page - 24 - 31
Reissued: August 1, 1986