CHAPTER...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

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.


mailto:[email protected]

http://www.cirrusdesign.com/

TABLE OF CONTENTS

Subject Page Reference Section i-1

• Gauges, Annunciators, & Breakers i-1 • Run-up Test Card i-3 • Symptom Flow Chart i-4

Starter Failure 1-1

• Starter does not engage. 1-1 • Starter engages when Bat1 switch is toggled. 1-3

Alternator Failure & Annunciation 1-4

• Alt1 Fail Light is illuminated. 1-4 • Alt2 Fail Light is illuminated. 1-4 • Low Volts Light is illuminated. 1-8 • Alt Fail Light blinks consistently. 1-9 • Alt Fail Light does not illuminate when no current is indicated. 1-10

Loss of Power 1-12

• No power received when Battery 1 switch is activated. 1-12 • No external power. 1-13

Miscellaneous 1-14

• Ammeter pegs at ±60A, or reads abnormal 0A. 1-14 • Alternator circuit breakers trigger. 1-14 • Power remains when all Battery bolster switches are off. 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.

AnnunciatorPanel

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

StarterRelay

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.


Model:___________________ MCU100 TROUBLESHOOTING RUN-UP ALL SR22 AIRCRAFT Serial Number:____________ 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.

PRETEST RUN-UP FLOWCHART

MCU Troubleshooting Flowchart

Refer to page 1-14.

Power remains on afterall bolster switches have

been disabled.

All tests read normal.

Refer to page 1-4.

Alt 1 Fail Lightis illuminated.

Refer to page 1-4.

Alt 2 Fail Lightis illuminated.

Refer to page 1-8.

Low Volts Lightis illuminated.

Refer to page 1-9.

Alt Fail Light blinksconsistently

Refer to page 1-10.

Alt Fail Light does notilluminate when expected.

Annunciators donot read correctly.

Refer to page 1-14.

Current Pegsor reads zero Amps.

Plane starts normally.

Refer to page 1-1.

Starter will not engage.

Refer to page 1-3.

Starter engages withoutignition.

Refer to page 1-12.

No power is receivedwhen Bat1 switch is enabled.

Perform Runup Test


SECTION 1- STARTER FAILURE Symptom: Starter motor will not engage.

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:

• 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:


• 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:


• Remove the cowl of the aircraft.

• Locate the wiring harnesses protruding from the MCU.

• Disconnect P/J 108.

Refer to section 24-30-01 of the SR20/22 wiring manual for a wiring harness layout.


• 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.


SECTION 2- ALTERNATOR FAILURE & ANNUNCIATION

Symptom:

The Alternator Fail Light for alternator X is illuminated. 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.

Please refer to Section 24-30 in the Maintenance manual for additional support.


• 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:

• 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.

• 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.


• 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:


• Enable Battery 1 power.


Refer to section 24-30-01 of the SR20/22 wiring manual for a wiring harness layout.


• 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:


• 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 Alternator 2- SR22

• Enable battery 1 power.


• 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.

What to do:

• Turn all aircraft power off.


• 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.


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:

• 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.



• 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:



• 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.


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.

• 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:

• Make sure that the pretest run-up has been performed, and the run-up table located on page 2 of this chapter has been properly filled out.


• 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.


SECTION 3- LOSS OF POWER

Symptom:

No power to the aircraft is obtained when activating the Master/Bat 1 bolster switch.

Possible Causes:

1. The Battery 1/Master bolster switch is inoperable. What to do:

• Make sure all power to the aircraft is turned off.


• 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:

• 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.


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:



• Disconnect the negative terminal from Battery 1.





(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:

• 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.


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.

What to do:


• Remove the cowl of the aircraft


Please refer to section 24-50, and also 39-10 for a description and layout of the bolster panel assembly.





(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:

• 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.


• 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.


• 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:

• 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.


• 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.


CHAPTER...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

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