C.  
Prepare to Remove the SCU

 S 864-004-N00
 (1)  
For the applicable engine, open these circuit breakers and attach the DO-NOT-CLOSE tags:

 (a)  
P6 Main Power Distribution Panel
 1) 6G15 SCU ALT PWR ENG 1
 2) 6G16 SCU ALT PWR ENG 2
 3) 6G17 SCU ALT PWR ENG 3
 4) 6G18 SCU ALT PWR ENG 4

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////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
SUPPLEMENTAL CONTROL UNIT (SCU), M6848SEE ASEE B
J1 ELECTRICAL
CONNECTOR
(DM6848A)

J2 ELECTRICAL
CONNECTOR

J3 ELECTRICAL
CONNECTOR

BOLT WASHER (4 LOCATIONS)
PACKING PROGRAMMING
ADAPTER
PLUG J5 ELECTRICAL
FAN CASE CONNECTOR (DM6848B) PT2.5 HOSE
FWD
SCU,
M6848

FAN CASE  A
BOLT
GROUND
STRAP

VIEW IN THE FORWARD DIRECTION
B
Supplemental Control Unit (SCU) Installation
Figure 401

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5) 6G23 ENG SCU 1
 6) 6G24 ENG SCU 2
 7) 6G25 ENG SCU 3
 8) 6G26 ENG SCU 4

 S 864-032-N00
 (2)  
Make sure the applicable engine AUTOSTART switch on the pilot's overhead panel, P5, is in the OFF position.

 S 014-002-N00

 (3)  
Open the right fan cowl panel (AMM 71-11-04/201).

 D.
Procedure

 S 024-035-N00
 (1)  Remove the SCU:
 CAUTION:_______DO NOT REMOVE THE PROGRAMMING PLUG FROM THE ENGINE. THE PROGRAMMING PLUG MUST STAY WITH THE ENGINE DURING THE SCU REPLACEMENT TO MAKE SURE THE ENGINE SERIAL NUMBER IS CORRECT.
 (a)  
Disconnect the programming plug from the J4 receptacle on the SCU. 1) Install a protection cap at the open end of the programming

 plug.

 (b)  
Disconnect the electrical connectors DM6848A and DM6848B from the J1 and J5 receptacles on the SCU. 1) Install the protection caps on the open ends of the

 electrical connectors.

 (c)  
Disconnect the electrical connectors from the J2 and J3 receptacles on the SCU. 1) Install the protection caps at the open ends of the

 electrical connectors.

 (d)  
Remove the bolt which attaches the ground strap to the top aft end of the SCU.

 (e)  
Disconnect the PT2.5 hose from the port at the bottom of the SCU. 1) Install the protection cap at the open end of the PT2.5

 hose.

 (f)  
Remove the bolts and washers which attach the SCU to the shockmounts and brackets.

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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(g)  Remove the SCU from the engine.
 S 024-028-N00
 (2)  
If it is necessary to replace the SCU, do the steps that follow:

 (a)  
Remove the adapter and gasket.
 1) Discard the gasket.

 S 024-029-N00
 (3)  Install the protection caps to the openings and receptacles on the SCU.
 TASK 73-21-15-404-008-N00
 3. Install the Supplemental Control Unit (SCU) (Fig. 401)
___________________________________________
 A. Consumable Materials
　
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