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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