A.  Trouble shooting the altitude alerting system is best accomplished by performing the system test (Ref 34-17-0, Adjustment/Test). Satisfactory completion of the system test procedure indicates that the system is operating properly. When satisfactory operation is not obtained, the tabulated data below should be consulted. If using the tabulated data fails to correct the trouble, airplane wiring should be suspect and repair or replaced as necessary.
TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
System completely  Circuit breaker  Check that system circuit  Close circuit 
inoperative  No power available to controller  breakers on P18 are closed Check 26V AC is available at pins U (high) and V (low) of plug connected to controller. If power is available, controller is faulty If power not available, airplane wiring at fault  breakers(s) Replace controller Refer to wiring diagram 
Altitude alert  Loss on 28V DC CADC  Check that 28V DC available  Refer to 34-12-0, 
controller failure  validity signal input  at pins W (high) and R (low)  Air Data Pressure 
monitor flag in view  Loss of 26V AC to controller  of plug connected to controller Check that 26V AC power available at pins U (high) and V (low) of plug connected to controller  Instrument Close circuit breaker 

504 
Feb 15/81  34-17-02 
Page 101 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

577 
34-17-02 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Sep 20/81 

ALTITUDE ALERTING SYSTEM - ADJUSTMENT/TEST
EFFECTIVITY
PI N789N FF ALL EXCEPT N37AF thru N58AF GJ ALL EXCEPT B-2509 thru B-2510
1.  Altitude Alerting System Test
A.  Equipment and Materials
(1)  
Air pressure and vacuum source, 5 to 40 inches of mercury absolute, and gage for measuring differential pressure, accurate within .0.015 inches of mercury. Range should be at least 10 inches of mercury.

(2)  
Air pressure and vacuum source, 5 to 30 inches of mercury absolute

(3)  
Pressure gage accurate to within .0.03 inches of mercury

(4)  
Appropriate gage saver restrictors

(5)  
Adequate lengths of hose to couple pressure source with pitot tubes and vacuum source with static ports or drains

(6)  
Pitot static probe adapter - P/N PSS-22300-4-6-6, NAV AIDS LIMITED; and alternate static port adapter - P/N F72823-40

B.  Prepare to Test Altitude Alerting System
(1)  To prevent damage to equipment and instruments, check following precautions before applying pressures to pitot static system
(a)  
Apply or release vacuum or pressure at rate of climb or descent less than 5000 feet per minute for static system and 300 knots per minute for pitot system between test points. (Appropriate gage saver restrictors should be used.) At each test point, pressure should be reduced slowly to desired level without overshoot.

(b)  
Pressure in pitot lines should always be greater than or equal to pressure in static lines. Differential pressure should never exceed 10.00 inches of mercury or fall below zero.

(c)  
Absolute pressure applied to static system should never exceed ambient absolute pressure when any instrument is connected to static system. 

Jun 20/83 34-17-02 Page 501
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

(d)  
Do not change setting of static source selector valve while vacuum is on static system. Check that selector valve remains in NORMAL position unless test procedures specify otherwise.

(e)  
Check that pitot static probe heaters remain off during tests.

(f)  
Inspect each pitot static probe head both before and after these tests for evidence of damage to circular leading edge of its barrel.

(g)  
Do not apply pressure in excess of 31 inches of mercury absolute to static lines.

CAUTION:  IF THE ABOVE PROCEDURES ARE NOT OBSERVED, EQUIPMENT AND INSTRUMENTS WILL BE DAMAGED.
(2)  
Connect pitot pressure source to upper left pitot static probe and static source to S1 port on upper left pitot static probe.

NOTE:  System drain fittings may be used for pitot and static pressure connections but are not the preferred connections.

(3)  
Seal S1 static port on lower right pitot static probe in such a way that removal of seal will be complete leaving no deposits or roughness in or about ports. Seal should be properly marked to prevent removal while test is in progress.
　
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