B.
Access
(1)
Location Zones
117/118 Electronics and Electronics Compartment - Left and Right
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747-400 MAINTENANCE MANUAL
(2) Access Panel
125B Access Door Electronics
C. Procedure - WIUs Continuity Check
S 012-029
(1) Remove the cargo lining from the aft side of the electronic rack:
(a)
Remove the bolts.
(b)
Remove the cargo lining.
S 492-069
CAUTION:_______YOU MUST PUT A ESD WRIST STRAP ON YOUR WRIST. YOU MUST CONNECT THE ESD WRIST STRAP TO THE ELECTROSTATIC GROUND RECEPTACLE ON THE WIU RACK. MAKE SURE THE ESD WRIST STRAP IS ON YOUR SKIN. IF THERE IS MATERIAL BETWEEN THE STRAP AND YOUR SKIN, THE GROUND CIRCUIT WILL NOT BE SATISFACTORY. THE ELECTRONIC SHELVES AND THE WIRES ARE CONNECTED TO ELECTROSTATIC SENSITIVE EQUIPMENT. IF YOU DO NOT CORRECTLY USE THE ESD WRIST STRAP, YOU CAN CAUSE MUCH DAMAGE TO THE EQUIPMENT.
(2) Attach a ESD wrist strap to your wrist.
NOTE: The ESD wrist straps are kept in bags at the ends of the
____
WIU racks (Fig. 201).
S 492-030
(3)
Attach the ESD wrist strap to the electrostatic ground receptacle on the WIU rack (Fig. 201).
S 012-070
(4)
Remove all the electronic boxes (black boxes) from the electronic shelves that are connected to system you will examine.
NOTE: Do not disconnect the wire connectors from the wire wrap
____
plugs on the back side of the WIUs.
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747-400 MAINTENANCE MANUAL
S 012-002
CAUTION:_______ BEFORE YOU DO THE CONTINUITY CHECK, YOU MUST REMOVE THE
EXTERNAL POWER, ENGINE GENERATOR POWER, APU GENERATOR POWER,
AND ALL BATTERY POWER. YOU MUST REMOVE THE ELECTRONIC BOXES
THAT ARE CONNECTED TO THE SYSTEM YOU WILL EXAMINE. WHEN YOU DO
A CONTINUITY CHECK, MORE VOLTAGE AND AMPERAGE THAN THE SYSTEM
CAPACITY IS NECESSARY. DAMAGE TO THE EQUIPMENT CAN OCCUR IF
YOU DO NOT OBEY THIS CAUTION.
CAUTION: DO NOT PERMIT CONTAMINATION IN THE WIU WHEN THE COVER IS OFF.
_______ MAKE SURE THAT YOU KEEP CONTAMINATION OR UNWANTED MATERIAL AWAY FROM THE WIU. MAKE SURE THAT OTHER PEOPLE THAT WORK AROUND THE WIU AREA KEEP UNWANTED MATERIAL OR CONTAMINATION AWAY FROM THE WIU. UNWANTED MATERIAL OR CONTAMINATION CAN CAUSE A MALFUNCTION IN THE WIU.
(5) Remove the WIU cover from the applicable shelf:
(a)
Remove the bolts that hold the WIU cover (View B, Fig. 201). NOTE: Do not loosen the center bolt at the top of the cover.
____ The bolt at this location is a slot and does not hold the cover.
(b)
Remove the cover.
S 762-032
CAUTION:_______DO NOT REMOVE THE POST COVER FROM THE WIRE WRAP POSTS. SPARKS BETWEEN THE POSTS CAN CAUSE DAMAGE TO THE EQUIPMENT.
(6) Do the continuity check in this sequence:
(a) Put the insulated sockets on the applicable wire wrap posts (View D, Fig. 201).
NOTE: You can make a insulated socket from a No. 16 connector
____ socket. Attached it to a connector socket of the correct size to fit the probe point of the continuity checker (Fig. 202).
(b) Do the continuity check to each wire from each electronic box connector to the opposite electronic box connector.
NOTE: Do this to all the wires in the system before you do the
____
subsequent step.
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