(a)
On the Nose Cargo Door Power panel H122:
1) DOOR LIFT
2) PULL UP CAM
3) LATCHES 1-4R
4) LATCHES 1-4L
5) LATCHES 5-8R
6) LATCHES 5-8L
E.
Procedure
S 765-007
(1)
Do a check for a shorted diode in the latch actuator:
(a)
Connect voltmeter to the terminal block TB325-G4 in the H122 panel.
(b)
Hold the door control switch in OPEN position and read the DC voltage on the voltmeter.
(c)
If the voltage is less than 1 volt DC, then there is no shorted diode in the latch actuator.
(d)
If the voltage is 1 volt DC or more, then there is a shorted diode in the latch not-closed circuit (pin 17 on the latch actuator connector).
(e)
Disconnect voltmeter from the terminal block TB325-G4 in the H122 panel.
(f)
Connect voltmeter to the test point TP-3 in the H122 panel.
(g)
Hold the door control switch in CLOSE position and read the DC voltage on the voltmeter.
(h)
If the voltage is less than 1 volt DC, then there is no shorted diode in the latch actuator.
(i)
If the voltage is 1 volt DC or more, then there is a shorted diode in the latch not-open circuit (pin 11 on the latch actuator connector).
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52-31-05
ALL ú ú 02 Page 502 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
S 765-008
(2)
If a shorted diode is in the latch not-closed circuit (pin 17), do these steps to isolate the defective latch actuator:
(a)
Remove the DO-NOT-CLOSE tag and close this circuit breaker:
1) On the Nose Cargo Door Power panel H122: a) LATCHES 5-8L
(b)
Connect voltmeter to the terminal block TB325-G4 in the H122 panel.
(c)
Hold the cargo door switch in OPEN position to open the latch actuators 5L thru 8L.
(d)
Continue to hold the cargo door switch in OPEN position and read the DC voltage on the voltmeter. 1) If the voltage is 1 volt DC or more, then the shorted diode
is in one or more of the remaining latch actuators. 2) If the voltage is less than 1 volt DC, then the shorted diode is in this group of latch actuators.
(e)
Continue to do a check for the shorted diode in the remaining groups of latch actuators with each of these circuit breakers closed:
NOTE: Close each circuit breaker and do a voltage check until
____ you find the group of (4) latch actuators that has a shorted diode. You will have to find the defective latch actuator in this group before you do a check for the remaining group (s) of the latch actuators.
1) LATCHES 1-4L
2) LATCHES 1-4R
3) LATCHES 5-8R
(f) FOR A GROUP OF (4) LATCH ACTUATORS THAT HAS A SHORTED DIODE; Do these steps to find the defective latch actuator: 1) Open the applicable circuit breaker that contains a shorted
diode.
2) With the door control switch held in OPEN position, manually crank each latch actuator a minimum of 25 turns in the closed direction.
3) If the voltmeter reads 1 volt DC or more, then the actuator is defective.
(g) Replace the defective latch actuator (Ref 52-31-05/401).
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52-31-05
ALL ú ú 02 Page 503 ú Feb 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
S 765-009
(3)
If a shorted diode is in the latch not-open circuit (pin 11), do these steps to isolate the defective latch actuator:
(a)
Remove the DO-NOT-CLOSE tag and close this circuit breaker:
1) On the Nose Cargo Door Power panel H122: a) LATCHES 5-8L
(b)
Connect the voltmeter to the test point TP-3 in H122 panel.
(c)
Hold door control switch in CLOSE position to close the latch actuators 5L thru 8L.
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