(g)  
Release the TEST 2 button.

 (h)  
Make sure that the APU SQUIB TEST light goes off.

 (i)  
Push and hold the TEST 1 and the TEST 2 buttons on the P461 panel at the same time.

 (j)  
Make sure that the APU SQUIB TEST light stays off.

 (k)  
Release the TEST 1 and the TEST 2 buttons.

 (5)  
Remove electrical power if it is not necessary (Ref 24-22-00/201).

 S 865-023
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747-400 MAINTENANCE MANUAL
 LOWER CARGO COMPARTMENT SMOKE DETECTION SYSTEM - DESCRIPTION AND OPERTION
_________________________________________________________________________
 1.  General_______
 A.  Dual smoke detection systems are installed in the forward, aft, and bulk cargo compartments. These systems monitor smoke in air in the cargo compartments, and provide alerts for smoke conditions.
 B.  Each lower cargo compartment is divided into four smoke detection zones. There are eight (two on each zone) smoke detectors on the forward lower cargo and eight (two on each zone) more on the aft lower cargo compartment. The smoke detectors are located along the ride side of the compartments.
 C.  The two systems use DC power from 28 volts DC bus No.1. The system circuit breaker is located on P7 overhead circuit breaker panel.
 D.  The cargo smoke detection system is a draw-through air sampling system. A venturi ejector using bleed air, creates a vacuum which pulls the sample air through the system. Multiple pick-up points are provided in each of the smoke zones in both the forward, aft, and bulk compartments.
 E.  The operation of both systems are the same. Both systems normally operate in AND logic. Thus, both detectors of a system must sense smoke in order for a fire alarm to be given. The AFOLTS card in the system will automatically reconfigure the smoke detectors to single unit operation during system test with a detector failure.
 2.  Smoke Detector (Fig. 1)______________
 A.  The detector consists of a photocell and pilot light (LED in some airplanes) in a light-proof chamber plus associated amplifier, output, and test circuits on a printed circuit board. The detector has inlet and outlet tubes to provide air and smoke.
 B.  Smoke entering the light-proof chamber reflects the light from the pilot lamp (LED on some airplanes) onto a photocell. Then the photocell causes an increase in output voltage and a signal is relayed to the flight deck. The generated signal illuminates a light on the P5 pilot's overhead panel, creates an EICAS message, and activates MAWEA.
 3.  Smoke Detector Ejector (Fig. 1)______________________
 A.  The vacuum for the main manifold is created by a venturi ejector on the forward end of the aft cargo compartment. The ejector receives bleed air from the pneumatic system crossover duct.
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747-400
MAINTENANCE MANUAL

MISCELLANEOUS
FIRE CONTROL
SWITCHING
MODULE, M7326
MODULE, M7317
SEE B
SEE A
CARD FILE, M826
FIRE DETECTION

ELECTRICAL/ELECTRONICS EQUIPMENT COMPARTMENT CENTER
FIRE/OVHT
FIRE/OVHT
TEST
TEST SWITCH
A
SMOKE INDICATIONB
LIGHT (RED)
Lower Cargo Compartment Smoke Detection System Component Location Figure 1 (Sheet 1)
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747-400
MAINTENANCE MANUAL

AFT CARGO

SMOKE DETECTOR PAIR -SEE
　
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