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CHAPTER
CIRRUS DESIGN
MASTER CONTROL UNIT
MODEL MCU100
Rev. 4
4 September 2003
CHAPTER 1- MASTER CONTROL UNIT MODEL MCU100
Description:
The Master Control Unit Model MCU100 was designed for use in all Cirrus
Design SR22 aircraft, as well as all SR20 aircraft with serial numbers 1268
and subsequent.
The Master Control Unit, hereafter referred to as the MCU, provides
redundant power distribution to all of the aircraft’s instruments, lights, and
other electronic devices, with the exception of the emergency locator
transmitter (ELT).
Documentation Available:
In addition to this troubleshooting guide, additional publications are
available for purchase from Cirrus Design. For purchase information,
contact Shelly Storms by phone at 218-788-3134, or by email at
[email protected]. The Following publications are available for
the SR20 and SR22 models:
• Aircraft Maintenance Manual
• Aircraft Wiring Manual
• Illustrated Parts Catalog
• Pilot’s Operating Handbook
NOTE: The Handbook is also available for download on the Cirrus Design
Website at www.cirrusdesign.com under the Service and Upgrades
tab.
Rev. 4
4 September 2003
TABLE OF CONTENTS
Subject
Page
Reference Section
•
•
•
Gauges, Annunciators, & Breakers
Run-up Test Card
Symptom Flow Chart
Starter Failure
•
•
Starter does not engage.
Starter engages when Bat1 switch is toggled.
Alternator Failure & Annunciation
•
•
•
•
•
Alt1 Fail Light is illuminated.
Alt2 Fail Light is illuminated.
Low Volts Light is illuminated.
Alt Fail Light blinks consistently.
Alt Fail Light does not illuminate when no current is indicated.
Loss of Power
•
•
No power received when Battery 1 switch is activated.
No external power.
Miscellaneous
•
•
•
Rev. 4
Ammeter pegs at ±60A, or reads abnormal 0A.
Alternator circuit breakers trigger.
Power remains when all Battery bolster switches are off.
4 September 2003
i-1
i-1
i-3
i-4
1-1
1-1
1-3
1-4
1-4
1-4
1-8
1-9
1-10
1-12
1-12
1-13
1-14
1-14
1-14
1-14
IMPORTANT GAUGES AND SWITCHES
ROCHESTER VOLT/AMMETER
The Rochester Volt/Ammeter indicates the voltage on the essential bus.
By using the Ammeter Select Switch, the meter displays currents produced by
alternator 1, alternator 2, or battery 1.
Annunciator
Panel
CLOCK VOLTMETER
The Davtron clock has an internal digital voltmeter and outside air
temperature indicator. It indicates the non-essential bus voltage.
Rev. 4
4 September 2003
i-1
Annunciator
Panel
Alt 1
BAT 2
Alt 2
Starter
Relay
CIRCUIT BREAKER PANEL
The circuit breaker panel supplies power to most of the aircraft avionics
instruments by closing a power supply circuit to the labeled instrument on the
breaker panel. For some cases in this manual, a certain breaker may need to be
enabled or disabled to continue with a test procedure. The breakers are clearly
labeled on the panel as well as pointed to above if relevant to this chapter.
Rev. 4
4 September 2003
i-2
Model:___________________
MCU100 TROUBLESHOOTING RUN-UP
Serial Number:____________
ALL SR22 AIRCRAFT
SR20 SERIAL NUMBERS 1268 AND SUBSEQUENT
Perform runup:
NOTE: During this test, all power sources should be enabled unless otherwise
noted. (i.e. ALT 1, ALT 2, BAT 1, BAT 2 all on).
1. Run aircraft at or above 2200 RPM. ‰
2. Verify that ALL circuit breakers are in. ‰
3. Turn on Landing Light. ‰
4. Turn on Nav Lights. ‰
5. Turn on Avionics. ‰
6. Turn on Pitot Heat. ‰
7. ALT 1 ON, ALT 2 OFF. ‰
8. Fill in Line 1 of Table at right. ‰
9.
ALT 1 OFF, ALT 2 ON. ‰
10. Fill in Line 2 of Table at right. ‰
11. ALT 1 ON, ALT 2 ON. ‰
12. Fill in Line 3 of Table at right. ‰
13. ALT 1 OFF, ALT 2 OFF. ‰
14. Fill in Line 4 of Table at right. ‰
15. Date:_______________________
16. Time:_______________________
17. OAT:_______________________
18. Technician:___________________
19. Any Previous Repairs?:________
If yes, what?:_________________
___________________________
1
___________________________
1
* Line 1 condition, the Davtron clock voltage should read 0.7V above that of the Rochester Gauge.
Rev. 4
4 September 2003
i-3
PRETEST RUN-UP FLOWCHART
MCU Troubleshooting Flowchart
Perform Runup Test
Plane starts normally.
All tests read normal.
Annunciators do
not read correctly.
Starter will not engage.
Current Pegs
or reads zero Amps.
Power remains on after
all bolster switches have
been disabled.
Alt 1 Fail Light
is illuminated.
Alt 2 Fail Light
is illuminated.
Refer to page 1-14.
Refer to page 1-4.
Refer to page 1-4.
Low Volts Light
is illuminated.
Alt Fail Light blinks
consistently
Refer to page 1-8.
Refer to page 1-9.
Refer to page 1-14.
Refer to page 1-1.
Starter engages without
ignition.
Refer to page 1-3.
No power is received
when Bat1 switch is enabled.
Refer to page 1-12.
Alt Fail Light does not
illuminate when expected.
Refer to page 1-10.
Rev. 4
4 September 2003
i-4
SECTION 1- STARTER FAILURE
Symptom:
Starter motor will not engage.Ó
Possible Causes:
1. The circuit breaker for the Starter is tripped.
What to do:
•
Check the status of the Starter Relay circuit breaker on the circuit
breaker panel located at the pilot’s right knee.
•
If tripped, reset the circuit breaker and attempt to start the aircraft
again.
•
If the circuit breaker trips on a second attempt, then there may be a
short in the wiring between the circuit breaker panel and the MCU.
2. Loose connection between the MCU and the Starter motor.
What to do:
Ó
•
Turn off all aircraft power.
•
Remove the cowl of the aircraft.
•
Locate the aircraft’s Starter motor- It is located beneath the engine on
the copilot’s side, near the rear of the engine.
Please refer to Chapter 80 of the Maintenance manual for additional support.
Rev. 4
4 September 2003
1-1
•
Make sure all electrical connections to the starter motor are secure.
•
Turn power back on and attempt to start the aircraft.
3. The power relay for the Starter motor is damaged.
What to do:
•
Turn off all aircraft power.
•
Remove the cowl of the aircraft.
•
Locate the aircraft’s Starter motor as shown above.
•
Remove the positive connector from the starter motor. Connect a
voltmeter to this connector.
•
Enable Bat 1 power.
•
With the ignition switch in the start position, measure the voltage
between the positive connector and ground.
•
The measured voltage should be close to 24 volts.
•
If the voltage is zero, this could indicate a damaged starter relay
within the MCU. Check for bad wiring in the next section.
•
If 24 Volts is read at this point, disable all aircraft power and replace
the positive terminal to the starter motor. Make sure that the terminal
is tightly seated. Attempt to start the aircraft. If the starter motor still
does not engage, this indicates a damaged starter motor.
4. The wiring between the MCU and the starter switch is damaged.
What to do:
Ó
•
Turn off all aircraft power.
•
Remove the cowl of the aircraft.
•
Locate the wiring harnesses protruding from the MCU.Ó
•
Disconnect P/J 108.
Refer to section 24-30-01 of the SR20/22 wiring manual for a wiring harness layout.
Rev. 4
4 September 2003
1-2
•
Disconnect P/J 109.
•
Turn the starter switch to the start position.
•
With an ohmmeter, measure the resistance between pin E of P108
(the side coming from the cabin) and pin B of P109 (the side coming
from the cabin). Under normal conditions, this resistance should
read zero. If an infinite resistance is measured, this indicates
damaged wiring within the aircraft, or a faulty starter switch. Check
the condition of the following: P/J 109, P/J 108, starter switch.
5. The Starter motor is damaged/Inoperable.
What to do:
•
Perform tests as described in the bad starter relay section.
Symptom:
Starter motor engages when the battery 1 master bolster switch is toggled.
Possible Causes:
1. The Starter relay within the MCU is damaged (welded shut).
What to do:
• If this problem is encountered, the MCU must be sent in for service,
and the starter motor must be replaced.
Rev. 4
4 September 2003
1-3
SECTION 2- ALTERNATOR FAILURE & ANNUNCIATION
Symptom:
The Alternator Fail Light for alternator X is illuminated.Ó
Note: It is normal for the Alt 2 Fail light to be illuminated while the
engine is below 2200 RPM.
Possible Causes:
1. Alternator X circuit breaker is tripped.
What to do:
•
Check the status of the alternator circuit breakers on the circuit
breaker panel located by the pilot’s right knee.
2. The logic board/current sensor within the MCU is inoperable.
What to do:
•
Make sure the pretest run-up has been performed, and that the
table on page 2 of this chapter has been properly filled out.
•
Check the Alt 1 Fail light for proper annunciation.
1. Refer to line 1 of the run-up table.
2. Compare the currents/voltages from the run-up with the
normal voltages listed in the table.
3. If all currents/voltages are within normal ranges, and the
Alt 1 Fail light is illuminated, this may indicate a faulty logic
unit within the MCU. Before ordering a new unit, perform
the necessary checks described later in this section to
ensure there is not a short in the aircraft’s wiring.
4. If the current measured for Alt 1 reads zero or ±60A, this
indicates a faulty current sensor within the MCU.
Ó
Please refer to Section 24-30 in the Maintenance manual for additional support.
Rev. 4
4 September 2003
1-4
•
Check the Alt 2 Fail light for proper annunciation.
1. Refer to line 2 of the run-up table.
2. Compare the currents/voltages from the run-up with the
normal values listed in the table.
3. If all currents/voltages are within normal ranges, and the
Alt 2 Fail light is illuminated, this may indicate a faulty logic
unit within the MCU. Before ordering a new unit, perform
the necessary checks described later in this section to
ensure there is not a short in the aircraft’s wiring.
4. If the current measured for Alt 2 read zero or ±60A, this
indicates a faulty current sensor within the MCU.
3. The bolster switch for alternator X is inoperable.
What to do:
Ó
•
Disable all power to the aircraft by removing the negative terminal
from battery 1, and by pulling out the circuit breaker for battery 2.
•
Remove the bolster switch panel by removing the two screws at
either end.Ó
•
Remove the two wiring harnesses on the back of the bolster switch
assembly. They should be labeled P/J 660, and P/J 661.
Please refer to section 24-50, and also 39-10 for a description and layout of the bolster panel assembly.
Rev. 4
4 September 2003
1-5
•
To test the operation of the Alternator 1 bolster switch, use an
ohmmeter to measure the resistance between pin 5 and pin 7 of
J660 (the side that is connected to the bolster panel assembly). If
the bolster switch is operating correctly, the resistance should read
an open circuit when the switch is disengaged, and circuit continuity
when the switch is engaged.
•
To test the operation of the Alternator 2 bolster switch, use an
ohmmeter to measure the resistance between pin 5 and pin 7 of
P661 (the side that is connected to the bolster panel assembly). If
the bolster switch is operating correctly, the resistance should read
an open circuit when the switch is disengaged, and circuit continuity
when the switch is engaged.
4. There is a short circuit in the aircraft’s wiring between the annunciator
panel and the MCU.
What to do:
Ó
•
Remove the cowl of the aircraft.
•
Enable Battery 1 power.
•
Locate the wiring harnesses protruding from the MCU.Ó
Refer to section 24-30-01 of the SR20/22 wiring manual for a wiring harness layout.
Rev. 4
4 September 2003
1-6
•
To test Alt 1 and Alt 2 fail lights, disconnect P/J 111. You will notice
the Alt 1 and Alt 2 fail lights will go out immediately. If they remain
illuminated, this indicates a short circuit in the aircraft’s wiring.
Check the harness P/J 111 for bent pins or other damage.
Otherwise, the annunciator panel may need to be replaced.
•
To test the Low Volts annunciator, turn off battery 1 master power.
Disconnect P/J 108. This will disable main power. Attach pin D of
J108 (coming from the MCU) to ground in order to enable main
power again. If the Low Volts annunciator illuminates, this indicates
a short circuit in the aircraft’s wiring. Check the harness P/J 108 for
bent pins or other damage. Otherwise, the annunciator panel may
need to be replaced.
5. The field control module within the MCU is not working correctly.
What to do:
•
Remove the cowl of the aircraft.
•
Locate the alternator in question. Alternator 1 is near the front of
the engine, on the copilot’s side. Alternator 2 is near the rear of the
engine.
Alternator 1- SR22
•
Rev. 4
Alternator 2- SR22
Enable battery 1 power.
4 September 2003
1-7
•
To test the field module for alternator 1, measure the voltage
between the field input on the alternator and ground. Make sure
you leave the connectors connected to the alternator while
performing this measurement. If the field voltage module is working
properly, the voltage should read approximately 20-24 volts.
•
To test the field module for alternator 2, disconnect J125 from
alternator 2. Measure the voltage between one pin from J125 and
ground. If the field voltage module is working properly, the voltage
should read approximately 20-24 volts.
6. The alternator itself is damaged/inoperable.Ó
What to do:
•
Turn all aircraft power off.
•
Remove the cowl of the aircraft.
•
Locate the alternator in question. Alternator 1 is near the front of
the engine, on the copilot’s side. Alternator 2 is near the rear of the
engine.
•
For alternator 1, use an ohmmeter to measure the resistance
between the field connector and the ground (or case) of the
alternator. If the coil in the alternator is damaged, the resistance
will measure as an open circuit.
•
For alternator 2, remove J125 from the alternator, and measure the
resistance between one of the pins on the alternator and ground (or
case) of the alternator. If the coil in the alternator is damaged, the
resistance will measure as an open circuit.
Symptom:
The Low Volts Light is illuminated.
Note: It is normal for the Low Volts Light to be illuminated when the
aircraft’s engine is not running.
Possible Causes:
1. Both alternators are disabled.
Please refer to section 24-30, pages 15-17 in the SR20 Maintenance Manual, and section 24-30,
pages 6-8 in the SR22 Maintenance Manual.
Ó
Rev. 4
4 September 2003
1-8
What to do:
•
Make sure the pretest run-up is performed, and that the table on
page 1-2 has been properly filled out.
•
Refer to line 3 of the run-up table.
•
Compare the voltage measured on the Rochester Voltmeter the
normal voltage listed in the table.
•
If the measured voltage on the Rochester Gauge was normal, and
the Low Volts Light was still illuminated, this may indicate a faulty
logic unit within the MCU. Before ordering a new unit, perform the
tests necessary to ensure there is not a short in the aircraft’s wiring.
Refer to page 1-6 for proper procedures.
2. The bolster panel switches for the alternators are bad.
What to do:
•
Refer to page 1-5 for instructions on checking the bolster panel
assembly.
3. The field control modules located within the MCU are faulty.
What to do:
•
Refer to 1-7 for instructions on checking the operation of the field
control modules.
Symptom:
Alt Fail Light for alternator X blinks consistently.
Possible Causes:
1. The logic unit/current sensor located within the MCU is faulty.
What to do:
Rev. 4
•
Make sure that the pretest run-up has been preformed, and that the
table on page 2 of this chapter has been properly filled out.
•
Refer to line 3 of the run-up table.
4 September 2003
1-9
•
Compare the current for alternator X with the normal current in line
3.
•
If the currents are within normal values, this indicates a faulty logic
unit within the MCU.
•
If the current read zero or ±60A, this indicates a faulty current
sensor within the MCU.
If a bad logic board is suspected, turn the alternator in question off.
The Alt Fail light should stop blinking and become solid. If they
continue blinking or stop illuminating, this confirms a faulty logic
board within the MCU.
•
Symptom:
Alternator X Fail Light does not illuminate, and ammeter shows no current
for alternator X.
Possible Causes:
1. The circuit breaker for the annunciator panel is tripped.
What to do:
•
Locate the circuit breaker labeled “Annunciator” on the circuit
breaker panel located by the pilot’s right knee.
•
Verify that the circuit breaker is pushed in.
•
Test the functionality of the annunciators by activating the
annunciator test switch.
2. A wiring harness may be loose.
What to do:
•
Remove the cowl of the aircraft.
•
Locate the wiring harnesses protruding from the MCU.
•
Make sure all harnesses are firmly connected together.
3. There is an open circuit in the aircraft’s wiring between the annunciator
panel and the MCU.
Rev. 4
4 September 2003
1 - 10
What to do:
•
To test the wiring harnesses for alternator 1 and alternator 2
annunciators, remove the cowl of the aircraft.
•
Enable Bat 1 power.
•
Locate the harnesses protruding from the MCU and disconnect
P/J 111.Ó
•
Attach pin F of P111 (coming from the aircraft) to the chassis of the
MCU. The Alt 1 fail annunciator should illuminate. If it does not,
this indicates either bad wiring to the annunciator panel, or a faulty
annunciator. Check the J111 for bent pins or other damage.
Otherwise, the annunciator panel may need to be replaced.
•
Attach pin G of P111 (coming from the aircraft) to the chassis of the
MCU. The Alt 2 fail annunciator should illuminate. If it does not,
this indicates either bad wiring to the annunciator panel, or a faulty
annunciator. Check the J111 for bent pins or other damage.
Otherwise, the annunciator panel may need to be replaced.
4. The logic unit in the MCU is inoperable.
What to do:
Ó
•
Make sure that the pretest run-up has been performed, and the runup table located on page 2 of this chapter has been properly filled
out.
•
Refer to line 4 of the run-up table.
•
Compare the measured voltages to the normal voltages indicated in
the table. If the voltages match, all annunciators should be lit. This
is also shown in the table. If any of the annunciators are not lit, this
indicates a faulty logic unit within the MCU.
Refer to section 24-30-01 of the SR20/22 wiring manual for a layout of the wiring harnesses.
Rev. 4
4 September 2003
1 - 11
SECTION 3- LOSS OF POWER
Symptom:
No power to the aircraft is obtained when activating the Master/Bat 1
bolster switch.Ó
Possible Causes:
1. The Battery 1/Master bolster switch is inoperable.
What to do:
•
Make sure all power to the aircraft is turned off.
•
Remove the cowl of the aircraft.
•
Disconnect the negative terminal from Battery 1.
•
Locate the four wiring harnesses protruding from the MCU.
•
Disconnect P/J 108. It is one of the harnesses protruding from the
MCU.
•
Activate the Battery 1/Master bolster switch.
•
With an ohmmeter, measure the resistance between pin D of P108
(the end coming from the rest of the aircraft), and the chassis of the
MCU. If the switch is operating correctly, the resistance should
read circuit continuity. If it reads an open circuit, this indicates a
faulty Battery 1/Master bolster switch and it must be replaced.
•
If a bolster switch is found to be good, the problem could be caused
by a bad solenoid within the MCU, or a blown fuse within the MCU.
In either case, the MCU must be sent in for service.
2. The Battery 1 solenoid within the MCU is damaged.
What to do:
•
Ó
Follow the instructions above to check for a faulty bolster switch. If
the switch tests functional, this indicates a damaged MCU solenoid.
Please refer to section 24-30 for information on MCU placement.
Rev. 4
4 September 2003
1 - 12
Symptom:
No external power is available when Battery 1/Master bolster switch is
activated.
Possible Causes:
1. The Battery 1 bolster switch is inoperable.
What to do:
•
Make sure all power to the aircraft is turned off.
•
Remove the cowl of the aircraft.
•
Disconnect the negative terminal from Battery 1.
•
Locate the four wiring harnesses protruding from the MCU.
•
Disconnect P/J 108. It is one of the harnesses protruding from the
MCU.
•
Activate the Battery 1/Master bolster switch.
•
With an ohmmeter, measure the resistance between pin D of P108
(the end coming from the rest of the aircraft), and the chassis of the
MCU. If the switch is operating correctly, the resistance should
read circuit continuity. If it reads an open circuit, this indicates a
faulty Battery 1/Master bolster switch and it must be replaced.
2. The external power solenoid within the MCU is faulty.
What to do:
Rev. 4
•
Make sure the Battery 1 bolster switch is functioning. Follow the
instructions above for details on testing the Battery 1 bolster switch.
•
Make sure the external power plug is securely plugged into the
external power jack.
•
If external power is still not available, this indicates a faulty solenoid
within the MCU.
4 September 2003
1 - 13
SECTION 4- MISCELLANEOUS
Symptom:
Ammeter pegs at ±60Amps, or the ammeter reads an abnormal 0A.
Possible Causes:
1. Faulty current sensor unit within the MCU.
What to do:
•
The MCU must be sent in to service.
Symptom:
Alternator X circuit breaker triggers.
Possible Causes:
1. The voltage regulators within the MCU are not regulating voltage properly.
What to do:
•
The MCU must be sent in to service.
Symptom:
Aircraft power remains on after all master switches are disengaged.
Possible Causes:
1. The Battery 1/Master bolster switch is inoperable.Ó
What to do:
Ó
•
Make sure all power to the aircraft is turned off.
•
Remove the cowl of the aircraft
•
Locate the four wiring harnesses protruding from the MCU.
Please refer to section 24-50, and also 39-10 for a description and layout of the bolster panel assembly.
Rev. 4
4 September 2003
1 - 14
•
Disconnect P/J 108. It is one of the harnesses protruding from the
MCU.Ó
•
Activate the Battery 1/Master bolster switch.
•
With an ohmmeter, measure the resistance between pin D of P108
(the end coming from the rest of the aircraft), and the chassis of the
MCU. If the switch is operating correctly, the resistance should
measure zero. If it reads overload or infinite, this indicates a faulty
Battery 1/Master bolster switch and it must be replaced.
•
If the Battery 1/Master bolster switch is operating correctly,
continue to the next possible cause.
2. The power relay for Battery 1 within the MCU is damaged (welded shut).
What to do:
•
If this problem is encountered, the MCU must be sent in for service.
Symptom:
The landing light is inoperable.
Possible Causes:
1. The landing light bolster panel switch is inoperable.
What to do:
Ó
•
Ensure all aircraft power is disengaged by setting all master bolster
panel switches to the off position.
•
Remove the cowling of the aircraft.
•
Locate the four wire harnesses protruding from the MCU.
•
Disconnect P/J 108.
•
Set the landing light bolster panel switch to the on position.
Refer to section 24-30-01 of the SR20/22 wiring manual for a layout of the wiring harnesses.
Rev. 4
4 September 2003
1 - 15
•
Using an ohmmeter, measure the resistance between pin J of P108
(coming from rest of aircraft) and the negative terminal of battery 1.
•
Circuit continuity should be present under normal conditions. If
circuit continuity is NOT found, this indicates an inoperable landing
light bolster panel switch.
2. The landing light relay within the MCU is inoperable.
What to do:
Rev. 4
•
Disable all aircraft power by setting all master bolster panel switches
to the off position.
•
Remove the cowling of the aircraft.
•
Locate wire harness P/J108 protruding from the MCU.
•
Disconnect P/J 108.
•
Attach a 20AWG wire from pin D of J108 to ground. This will enable
battery 1.
•
Attach a 20AWG wire from pin J of J108 to ground. This will trigger
the landing light relay.
•
Measure the voltage between pin K of J108 and ground.
•
If a reading of zero volts is measured, this indicates a faulty landing
light relay.
4 September 2003
1 - 16