Jan 10/9030-20-00
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
B. Fault Isolation(continued)
CHART 1 (Sheet 3 of 5)
FAULTISOLATION(ENGINEDEICING SYSTEM)
Fault Cause Remedy
Ammetershow low current over entire cycle. Aircraft voltage low. Check voltage into switch.
Ammeter faulty. Test for voltage up to and
out of ammeter. If low
or zero outputand input
satisfactory,replaceammeter. If no voltage or ammeter,
locate and fix break between
switch and ammeter.
High resistance up to Check for partially broken
timer. wire, loose or corroded
connectionin wiring from
aircraftsupply to timer
input.
Ammeter shows excess Ammeterfaulty. Test for voltage up to and
current over entire cycle. out of ammeter. If low or
zero output and input
satisfactory,replace
ammeter. If no voltage
to ammeter, locateand
fix break between switch
and ammeter.
Ground between ammeter Disconnectharnessat timer
and timer. andwith ohmmeter check
from Pin B (or harness)
to ground. If ground is
indicated. locate and correct
short.
Ammeter shows normal Ground between timer and Disconnectleads at brush
current part of cycle, brush block. blockand, with ohmmeter,
excess current rest of check from powerleads to
cycle. ground. If ground is indi-
cated, locate and correct
short.
Ground between brush If no short exists at
block and deicers. brush-slipringcontact
(Excludingground checkfor ground from
brush circuit.) slip ring lead to propeller
assemblywhileflexing
slip ring and deicer leads.
If a ground is indicated,
locate and correct short.
EFFECTIVITY:
040-999
30-20-00Jan 10/90
PAGE 3
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
B. FaultIsolation (continued)
CHART1 (Sheet4 of 5) FAULT ISOLATION (ENGINE DEICING SYSTEM)
Fault
Ammetershows normal currentpart of cycle, excesscurrentrest of cycle. (continued)
Ammeterdoesnot "flick"approximately every34 seconds.
Ammeter flicks between 34 second phase periods.
Cause
Shortbetween two adjacentcircuits.
Timer faulty.
Timer ground open.
Timercontactsare welded (causedby short circuit in system).
Loose connection between aircraft power supply andtimer output.
Looseor poor connection timer to deicers.
Timer cycles erratically.
Remedy
Checkfor cuts or low
resistancebetweencircuits. If any, locateandcorrect.
Testtimer.
Disconnectharnessat timer
and check with ohmmeter from Pin G (of harness) to ground. If no circuit, fix breakper schematicdiagram.
Test timer. If timer does not cyclewith voltageat Pin B, replacetimer but be sure shortcausingoriginalfailure hasbeen locateand corrected.
If trouble occurs over entire cycle, trace wiringfrom powersourceto timer input to locateand tighten loose
connection.
If trouble occurs in part of cycle,findwhichdeicers areaffectedandcheckfor
roughor dirty slip rings causingbrushto "skip" or poor connection at plug. If not this, tracecircuits to locate andfix loose or
poorconnection. (If all
heaterson one deicerare
affected,check the ground
circuit.) Flex deicer straps
for break in deicer straps.
Test timer.
EFFECTIVITY:
040-999
PAGE4 30-2000
Jan10/90
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
B. Fault Isolation(continued)
CHART 1 (Sheet 5 of 5)
FAULT ISOLATION (ENGINEDEICINGSYSTEM)
Fault Cause Remedy
Radionoise or interference withdeicerson. Brushes "arching." Check brush alignment as shown in 30-60-00,Figures
502 and 509. Look for
roughor dirty slip rings. If this
is the cause, clean machine or
replace slip ring assembly,
as required. Check slip ring
alignment.
Loose connection. Refer to Ammeter flicks
between 34 seconds phase
periods.
Switch faulty. Try jumper wire across
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