MOONEY INTERNATIONAL CORPORATION
M20V SERVICE AND MAINTENANCE MANUAL
Page
Date
9
MAR 2017
Rev Date
TROUBLESHOOTING - GENERAL (APAC)
Check the 5 Amp breaker, ALT switch and connections
between the Buss and the input to the APAC (i.e. pin 5)
for high resistance or intermittent connection.
No Voltage Regulation
With the master switch ON and battery voltage mea-
sured on the APAC input, the APAC output (blue wire)
voltage should be 0.5 to 2V less the Buss voltage.
If there is no Buss voltage on the APAC input (pin 5),
look for a broken wire, bad connection or input device
(5A circuit breaker or Alt switch) between the APAC and
the Buss.
If the input voltage is more than 0.2V lower than the
Buss voltage, look for and correct or replace the input
device that is causing the problem. The device has high
resistance.
If the output voltage on pin 7 is close to 0 volt and the
inputs (pins 5 and 8) have battery voltage, look for a
grounded alternator field or field wire (indicated by a
Red Troubleshooting Light TSL on the APAC). If the
field resistance is correct as shown in step 5 of the
Troubleshooting tests and the TSL is Off, send the
APAC in for test/repair.
If the TSL is Red, repair the field ground fault or open
Remote Voltage Sense (pin 8) wire or replace the alter-
nator.
If the output voltage is the same as the input voltage,
look for an open alternator field or field wire. If the field
resistance is higher than what is shown in step 5 of the
installation tests, send the alternator in for test/repair. If
the field resistance is correct, send the APAC in for test/
repair.
Buss voltage remains at battery voltage (about 24V)
To solve this problem, see No voltage regulation or AOI
stays On.
Alternator carries about half its rated output
Some of the reason this problem may happen are:
One or more of the alternator stator leads becomes
open, making the alternator supply current from only
one or two phases of its three. The same will happen if
one or more of the six rectifying diodes is open.
Resistance build- up or poor connection in the current
path between the output of the alternator and the Buss
can cause voltage drops that increase with increasing
Buss load. Poor connection between the load shunt
and the ammeter may also give false load indication.
Buss voltage drops with load increase.
See Alternator carries only about half its rated output.
Alternator drops off- line during run- up.
If the alternator drops off- line during run- up, check the
color of the TSL. Red means that the field is grounded
or the Remote Voltage Sensor wire (pin 8) is open/bro-
ken. A Green TSL indicates an open field wire or a “fly-
ing- open” field connection in the alternator’s field.
Alternator Out Indicator (AOI) stays on always.
If AOI is on when the Buss is at 28V, look for a broken
wire or open circuit between the APAC and AUX termi-
nal of the ALT.
If AOI is on and the Buss is at <26V with a 20A load on
the Buss at greater than 1600RPM, see if the TSL is
Red. If it is, the APAC dropped off- line due to field-
ground short, OV trip or loss of RS input (pin 8) due to
open circuit or high resistance, of there is no current
getting to the APAC.
MAIN ALTERNATOR TROUBLESHOOTING TESTS
1. Read previous APAC overview, maintenance and
Troubleshooting sections.
2. Check for and replace open, frayed or broken
wires. Thoroughly clean or replace corroded, dirty or
oxidized connections, terminals, contact or properly
soldered wire junction.
3. Check for open or ground- short alternator field.
Most 24V alternators have 10- 20Ω field resistance.
Ground shorted alternator field will damage most
ACUs. Repair or replace an alternator that has a field to
ground to short. The APAC will turn itself Off and the
APAC’sTSLwillturnRedifthereisafield-Gndshort.
4. With the engine Off: Check voltage drops across
the Field, Alt switch, Alt field circuit breaker and APAC.
High voltage- drop means excessive junction resist-
ance and will lead to many problems like; fluctuating
ammeters, charge- meters and panel lights.
5. Perform and record the following tests with the
MASTER SWITCH OFF:
-
Values (Typ) Value
A. Field resistance at
ALT
______Ω 10- 20Ω
B. Field resistance at
APAC
______Ω 10- 20Ω
C. Field SW resist-
ance
______Ω 0- 0.1Ω
D. Field C/BKR resist-
ance
______Ω 0- 0.05Ω
E. ALT Out C/BKR re-
sistance
______Ω 0- 0.05Ω
6. Perform and record the following tests with the
MASTER SWITCH ON:
-
Values (Typ)Value
A. Buss Volt Engine
Off
______V 23- 26V
D. APAC/Reg Input
Volt
______V 23- 26V
F. Field Voltage ______V
0.5-
2V<VBus
24-31-02
To Next Page
Loading...
