B.  Remove the IRS MSU.
 S 864-002
 (1) Open these circuit breakers and attach the DO-NOT-CLOSE tags:
 (a)  P6 Main Power Distribution Panel
 1) 6D7 IRS AC LEFT
 2) 6D8 IRS AC CENTER
 3) 6D9 IRS AC RIGHT
 4) 6E7 IRS DC LEFT
 5) 6E8 IRS DC CENTER
 6) 6E9 IRS DC RIGHT

 S 864-020
 (2)  Do these steps to remove the MSU.
 (a)  
Release the quick-release fasteners on the front of the MSU.

 (b)  
Lower the MSU from the P5 Overhead Panel.

 (c)  
Disconnect the electrical connectors from the rear of the MSU.

 TASK 34-21-02-404-007
 3.  Install The IRS Mode Select Unit________________________________
 A.  References
 (1)  24-22-00/201, Manual Control
 B.  Access
 (1)  Location Zone
 221 Control Cabin, LH

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MAINTENANCE MANUAL

MODE SELECT UNIT
SEE A
FLIGHT COMPARTMENT
ELECTRICAL CONNECTORS
FASTENER 
FASTENER  Figure 401 Mode Select Unit Installation A MODE SELECT UNIT  SWITCHES MODE SELECT 

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747-400 MAINTENANCE MANUAL
 C. Install the IRS MSU.
 S 864-008
 (1)  Make sure these circuit breakers are open with the DO-NOT-CLOSE tags attached:
 (a)  P6 Main Power Distribution Panel
 1) 6D7 IRS AC LEFT
 2) 6D8 IRS AC CENTER
 3) 6D9 IRS AC RIGHT
 4) 6E7 IRS DC LEFT
 5) 6E8 IRS DC CENTER
 6) 6E9 IRS DC RIGHT

 S 424-021
 (2)  Do these steps to install the MSU.
 (a)  
Connect the electrical connectors to the MSU.

 (b)  
Put the MSU in the P5 Overhead Panel.

 (c)  
Tighten the quick-release fasteners on the front of the MSU.

 S 864-017
 (3)  
Supply the electrical power (Ref 24-22-00/201).

 S 864-018

 (4)
Remove the DO-NOT-CLOSE tags and close these circuit breakers:

 (a)  P6 Main Power Distribution Panel
 1) 6D7 IRS AC LEFT
 2) 6D8 IRS AC CENTER
 3) 6D9 IRS AC RIGHT
 4) 6E7 IRS DC LEFT
 5) 6E8 IRS DC CENTER
 6) 6E9 IRS DC RIGHT

 (5)  
Set all three mode select switches on the MSU to ATT.

 S 714-022
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 (6)  S 714-023Make sure these messages show on the main EICAS display for 20 to 30 seconds: (a) IRS ALIGN MODE L (b) IRS ALIGN MODE C (c) IRS ALIGN MODE R
 (7)  S 864-024Set all three mode select switches on the MSU to OFF.
 (8)  S 864-016Remove the electrical power if it is not necessary (Ref 24-22-00/201).

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