777 AIRCRAFT MAINTENANCE MANUAL
ELMS -FUNCTIONAL DESCRIPTION -PANELS
EFFECTIVITY BEJ ALL 24-09-00
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D633W101-BEJ Jan 05/2002
ELMS -FUNCTIONAL DESCRIPTION -EEU
General
The power management panels contain ELMS electronic units (EEUs). The EEUs are two-channel computers that control and monitor load-switching devices in their related ELMS panels. Each EEU is an LRU that contains several circuit cards that are line replaceable modules (LRMs). These are the circuit cards in the P310 EEU:
*
Power supply
*
CPU
*
ARINC 629
*
DC subsystem
*
Special function
*
I/O-1
*
Filters A, B, and C.
P110 and P210 are similar except they do not contain a dc subsystem, special function, or filter B circuit card. They also use an I/O-2 card instead of an I/O-1 card.
Physical Description
The EEU is in a section of the power management panel that is shielded against EMI. You can remove the EEU from the panel. To remove the EEU from the panel, you must disconnect the electrical connectors on the side of the EEU and remove it from the panel.
The circuit cards are in slots in the EEU. All of the cards, except the filter cards, are color-coded and labeled on the front of the card. There is also a label on the door of the EEU that shows the equipment number for each card slot. Card locks hold the cards. To remove a card, loosen two card locks to release the card. To remove a filter card, you must first disconnect the electrical connector on the front of the card.
NOTE: The orientation of the P110 EEU is 180 degrees different
from P210 and P310 (channel A is on top and the filter
cards are to the right of the unit).
Power Supply
There are two power supply cards in each EEU. One is for channel A and the other for channel B. The power supplies change the airplane dc power into power for the EEU LRMs. The power supply cards are brown.
CPU
There are two central processing unit (CPU) cards in each EEU. One is for channel A and the other for channel B. The CPUs contain the software that controls and monitors the ELMS functions. The CPU cards have a red removal handle.
EFFECTIVITY BEJ ALL 24-09-00
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ELMS -FUNCTIONAL DESCRIPTION -EEU
The CPU channel that has the least failures is the channel in control. The circuitry that decides which channel to use is in both CPUs. If both CPUs are the same, the channel that was in control when power to the EEU was removed, is the channel in control. The channel in control changes when the engines are shutdown at the end of a flight leg.
The channel in control can receive and transmit data to the ARINC 629, I/O, dc subsystem, and special function cards. The other channel is in a standby mode and only receives data from the cards.
ARINC 629
There are two ARINC 629 cards in each EEU. The ARINC 629 cards transmit and receive data across the airplane systems ARINC 629 buses. One card is for the left systems bus and the other for the right systems bus. The ARINC 629 cards have a blue removal handle.
DC Subsystem
There is one dc subsystem card. It is in the P310 EEU. The dc subsystem card (DCS) controls and monitors the airplane dc system. The DCS card has a green removal handle.
The DCS card controls or monitors, and does an automatc test routine every 72 hours on, the relays that follow:
* K24006 -MAIN BATTERY RELAY
EFFECTIVITY
BEJ ALL
*
K24009 -AC STANDBY RELAY
*
K24013 -DC TIE RELAY
*
K24016 -CAPT/FO BUS TIE RELAY
*
K24017 -C1 TRU RELAY
*
K24018 -C2 TRU RELAY
*
K24019 -GROUND POWER BATTERY RELAY
*
K24020 -BAT-CAPT ISO RELAY
The DCS card also reports faults of the ELMS RAT DEPLOY circuit breaker (C24619).
Special Function
There is one special function card. It is in the P310 EEU. The special function card is an input/output (I/O) card and it controls the interface between special external signals and the CPUs such as the battery and TRU current sensors. The special function card converts certain, special signals from analog to digital for the processor, mostly those that control or monitor DC Standby functions and the Remote cabin pressure sensor. The special function card has a black removal handle.
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