MOONEY INTERNATIONAL CORPORATION
M20V SERVICE AND MAINTENANCE MANUAL
Page
Date
11
MAR 2017
Rev Date
coming out of the alternator. It should measure within
0.5 volts of the measurement on Terminal 5 of the regu-
lator. A lack of voltage may indicate an open circuit be-
tween Terminal 5 of the regulator and the field terminal.
If an open field circuit is suspected, the switches may
be turned off, the alternator field connector removed,
and a resistance measurement made between the con-
nector and Terminal 5 of the regulator. Look for near 0
Ohms. Typically the field resistance of the alternator
will be between 3 and 10 Ohms from the male field ter-
minal blade to alternator case.
Field Terminal Voltage
______v
Alternator field resistance
______Ω
6. With the switches on, check the voltage between
the alternator output post (or SBS lead) and ground. It
should be battery voltage. If not, check the wiring be-
tween the alternator SBS lead and the battery positive
(+) terminal. Look for loose or contaminated connec-
tions, broken wires, or an open breaker or fuse.
Alternator SBS Voltage
______v
7. If all of the voltages in the first 6 steps are close to
the value specified, the charging system should be op-
erative. If not, check for a broken or loose alternator belt
or, if the alternator is spline driven, check that the spline
drive shear coupling is not sheared. Note that on spline
drive alternators the engine speed must be at or above
run- up RPM before checking for useable output.
If the lamp circuit works properly but the lamp still re-
mains fixed either ON or OFF all the time with the lamp
wire connected to Terminal 2, assume that the lamp
driver is bad in the regulator. Have the regulator re-
paired or replaced.
If the charging system seems to be generating power,
but the STBY ALT ON annunciation will not flash above
20 amps output, check the following:
8. With the Battery and Standby Alternator Master
switches ON but the engine not running, check the volt-
age between terminals 4 and 7 of the regulator. The
voltage should be 10.0, 0.1volts.Ifitisnotwithintol-
erance, remove the wire from Terminal 4 and re- check
the voltage. If it is still not within tolerance the regulator
may be bad. If the voltage is now in tolerance, suspect a
bad current sensor or shorted sensor wire.
9. If the voltage originally measured in step 8 was in
tolerance, divide the measurement by 2. This value
should be the voltage measured between terminals 3
and 7 of the regulator. If the voltage measured is not
close to 5.0 Volts, suspect the current sensor in the
standby alternator output lead.
10. If the measurements in Steps 8 and 9 are satis-
factory, prepare to monitor the voltage between termi-
nals 3 and 7 of the regulator with the engine running.
Move the aircraft to a safe location for a 2000 RPM run-
up. Start the engine. Minimize the bus loads and bring
the engine RPM up to approximately 2000. Switch OFF
the primary alternator. Wait for the STBY ALT ON
G1000 annunciation to illuminate. At light bus loads this
could take a minute or two. Note the voltage between
terminals 3 and 7 of the regulator and begin switching
ON additional bus load. The monitored voltage should
increase at the rate of 0.056 Volts for each Amp of
standby alternator load.
a.) If the voltage does not change, verify standby
alternator output with the ship’s ammeter or a clamp-
on ammeter probe. If the standby output is verified and
there is still no change in the monitored voltage, sus-
pect a bad current sensor.
b.) If the voltage decreases instead of increasing,
the 10 Ga. current sensor wire is connected backward.
Reverse the connection and re- run the test.
c.) If the voltage increases at approximately the
correct rate, continue adding load until the voltage is
greater than 6.2 volts. At or above this voltage, the lamp
should be flashing. If not suspect a bad regulator.
TROUBLESHOOTING - NOISE (STANDBY ALT.)
Noise problems are also difficult to find. A few tips to
help with curing noise problems follow:
1. A unitized grounding system helps prevent noise
problems by preventing voltage differences between
different ground points.
2. The battery acts as a noise filter in the system.
Poor connections to the battery or a battery that is go-
ing bad can add to or even cause noise problems.
3. Shielding of low level audio leads (especially mi-
crophone leads or headset leads) is required. Some-
times the shields in the cables can separate from re-
peated flexing. Try checking shield continuity with an
ohmmeter or substituting another headset, micro-
phone, etc.
4. Wire routing may be important in some installa-
tions. Separation of noise carrying conductors such as
SPS leads from other wiring may help. Running noisy
wiring parallel to other wiring in the same bundle is ask-
ing for trouble. Wires at 90 degrees to one another,
however, do not couple noise.
5. Running transmitter feed lines close to and in par-
allel with other wiring can cause a problem. Normally,
problems will only be encountered if there is a mis-
match and therefore a high SWR in the antenna sys-
tem. If noise or charging system breaker tripping oc-
curs during Comm transmit only or when the
transponder is on only, check the corresponding anten-
na system carefully or separate the transmission line
from other wiring.
24-31-03
To Next Page
Loading...
