Generator Brush Inspection - Piper Cheyenne IIIA Airplane Maintenance Manual

PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. DC Generation (continued)
8. Checking Starter Generator System
The starter generator system incorporates two ammeters which provide an independent output
check of each generator and a voltmeter which monitors the electrical bus voltage. Should either
ammeter fail to indicate an output from its associated generator, check the appropriate circuit
breaker (refer to 24-61-02 wiring diagram manual). If the circuit breakers are in their normal
operating position, a further check of the system should be accomplished.
(a) Ensure that the ammeters are operating properly.
(b) Ensure that all electrical units are off and battery is fully charged.
(c) Disconnect electrical lead at terminal stud B+ on starter generator being tested (L or R).
(d) Turn on battery master switch and turn selector switch (L or R) for the unit being tested to the
START position.
(e) Using a voltmeter, attach positive lead to the electrical lead removed from terminal stud B+ on
starter generator and the other voltmeter lead to airframe ground. Voltmeter should read the
battery voltage of 24 volts.
(f) Turn battery master switch off.
(g) Disconnect the voltmeter positive lead from wire removed from starter generator terminal stud
B+.
(h) Connect electrical lead previously removed to B+ terminal stud on starter generator.
9. Generator Brush Inspection
Generator brush inspection is recommended at 100 hour intervals. By means of the diagonal wear
groove on the side of each brush, which shows 100% useful life when new, the percentage of
remaining useful life is easily estimated at each inspection. Inspect generator brushes as follows
to determine continued airworthiness:
(a) Remove brush cover from unit.
(b) Remove screws securing brush leads to brush holders. With a stiff wire hook, lift springs from
brushes and remove brushes.
NOTE: If brushes will be reused, mark each brush to allow that the brush will be installed into
brush holder that it was removed from.
(c) Determine remaining life of each brush (refer to Figure 601). If any one brush is estimated to
be worn out before the next inspection or overhaul, replace all brushes.
(d) After inspection, replace brush cover. Ensure that cover is seated in housing recess and that
exhaust air holes are located adjacent to terminal block.
(e) Install generator on aircraft.
(f) After inspection, replace brush cover. Ensure that cover is seated in housing recess and that
exhaust air holes are located adjacent to terminal block.
(g) Install generator on aircraft.
NOTE: Instant filming brushes which do not have cores or visible particles are identified by
marking I/F, in addition to any grade numbers and date code letters.
NOTE: If new brushes have been installed, it is not necessary to conduct seating or run-in
operations due to the ability of instant-filming brushes to carry full starting and
generating currents without such run-in. If the specified brush is NOT one of these
types, the unit must be returned to an overhaul shop for brush replacement, run-in,
and test.
EFFECTIVITY:
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040-999
Jan 10/90
24 3000