MAIN CARGO DOOR - TROUBLE SHOOTING
EFFECTIVITY
Passenger/Cargo Convertible Airplanes
1.  General
A.  Before using the trouble shooting chart, prepare to test operation of main cargo door in accordance with system adjustment/test procedures. Refer to 52-32-0. Troubles are presented on the chart in the order that they occur during the system test. Probable causes are presented according to the frequency in which they are most likely to occur.
B.  Control switches No. 1 and No. 2 and the amber door-unlocked light are on the main cargo door control panel. Both canopy position switches are adjacent to the bellcrank pivot point on the lift mechanism. The hydraulic control valve and the solenoid shutoff valve are on the left wheel well aft bulkhead.
C.  When hydraulic system B is inoperable, the main cargo door can be opened or closed by using the hand pump installed on the left wheel well aft bulkhead. Manual operation requires that the main cargo door control circuit breaker be pulled. This will remove all electrical power from the system. Refer to Manual Operation with Handpump, 52-32-0.
2.  Prepare to Trouble Shoot
A.  When trouble shooting the main cargo door in normal operation, ensure that the following conditions are in effect:
(1)  
Parking brake set.

(2)  
Hydraulic system B pressurized. Refer to Hydraulic Power, Chapter 29.

(3)  
Electrical power on.

(4)  
Door warning light on door warning module is operable. Refer to 52-71-0, Door Warning System.

(5)  
Lift actuator access door open.

May 15/69 52-32-0 Page 101
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

(6)  Deleted
B.  Prior to trouble shooting, ensure that the following circuit breakers on load control center P6 are closed:
(1)  
Hydraulic System B Pumps

(2)  
Main Cargo Door Control

(3)  
Landing Gear Failure Warning and Parking Brake

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52-32-0 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/75 

3. Main Cargo Door Trouble Shooting Chart
TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
1. Door unlocked light does not illuminate when door is unlocked  Defective light bulb or socket Defective wiring Defective lock mechanism or locked switch Defective wiring Defective door locked switch   Press-to-test door unlocked light. IF -A. Light does not illuminate--check for 28-v dc at terminal 1 of light socket. IF - (1) Voltage OK (2) No Voltage B. Light illuminates--check if cargo door warning light on door warning module is illuminated. IF -(1) Cargo door warning light is not illuminated (2) Cargo door warning light is illuminated. Check for continuity across terminals 10 and 11 of door locked switch. IF - (a) Continuity OK (b) No Continuity  Replace light bulb or socket Repair wiring between circuit breaker and light socket Adjust or repair lock mechanism or switch Repair wiring between switch ground and light socket Replace door locked switch 

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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
2. Door fails to raise when either switch held to open  Defective check valve, relief valve, flow limits, actuator, latch mechanism (door closed position)  Check position of control valve indicator. IF - A. Indicator at position 1--check if door raises in manual operations. IF -(1) Door still does not raise (2) Door raise--check for 28v dc at pin 1 and continuity to ground  Replace hydraulic component or adjust door latch mechanism (door does not unlock) 
Defective shutoff valve Defective landing gear safety circuit Defective control valve  at pin 3 of shutoff valve connector D1222. IF -(a) Voltage and ground OK (b) No ground at pin 3 (c) No voltage at pin 1— check for continuity across pins A and C of control valve and terminal 3C-3NO of respective control switch. IF -  1) No continuity across control valve pins A and C  Replace shutoff valve Refer to landing gear module M338 trouble shooting (32-09-100) Replace control valve 

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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
2.  Door fails to raise when either switch held open (cont.)  Defective control switch Defective wiring  2) No continuity across switch terminals 3) Continuity OK  Replace respective control switch Repair wiring between pin 1 of shutoff valve and pin 
　
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