C. BITE Operation (Airplanes with Fenwal compartment overhead accessory unit)
(1) The system has both hardware and software built in test features. A description of BITE follows and the BITE operating instructions are posted on the cover plate of the M237 module.
(a)
Pushing the OVHT TEST switch on the P5-10 panel tests all detectors for continuity and faults. All flight compartment displays of compartment overheat will display if each loop is operating correctly. Any faults detected during the test will be stored in the non-volatile memory for recall as required.
(b)
At the M237 compartment overheat accessory unit, pushing the DISP TEST switch initiates a self test of the display and associated circuits. Code 88 is displayed as long as the switch is held if there is no failed dc power source.
(c)
Momentarily pushing the LOC TEST switch initiates a self test of the control circuits code 90. If a fault condition is detected during the test sequence, the code for that fault condition is indicated by the display for approximately two minutes. Another momentary push of the LOC TEST switch during the 2-minute display interval causes the test sequence to continue. If not continued, the test sequence terminates after approximately 2 minutes. When the entire test sequence has been performed, code 99 is displayed for approximately 1\minutes. The test sequence initiated by the LOC TEST switch can be terminated at any time by pushing the DISP TEST switch.
(d)
When an alarm/fault condition is identified, the code is stored in the non-volatile memory for recall as required. The condition is stored in non-volatile memory until the condition is resolved, and the memory is cleared. The fault history stores the last ten codes that were cleared from the active non-volatile memory. Access to these functions is gained through the four BITE pushbutton switches on the M237 module cover plate (Ref 26-18-00 MP).
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Feb 20/90 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 26-18-0 Page 11
WING AND LOWER AFT BODY OVERHEAT DETECTION SYSTEM - TROUBLE SHOOTING
1. General
A. The two basic troubles which the wing and lower aft body overheat detection system may have are: a false alarm or no alarm. Proper utilization of the test switches within the system will isolate most trouble spots. The main system test switch is on air conditioning module P5-10. Pressing the switch should cause the overheat lights on the module to illuminate. If the right overheat light fails to illuminate, the right strut cavity sensor, right wing sensor, right air conditioning pack sensor or the right control unit in the compartment overheat accessory unit may be faulty. Trouble shoot per right overheat system trouble shooting chart. If the left overheat light on the module fails to illuminate, the left overheat sensors may be tested and isolated utilizing the toggle switches on the compartment overheat accessory unit. The toggle switches provide continuity and ground fault checks of each sensor. Trouble shoot per left overheat system trouble shooting chart.
NOTE: The Fenwal M237 control unit has an alarm threshold of approximately 115 ohms. The BECO M237 control unit has an alarm threshold between 25 and 50 ohms. Because of this, when you check the resistance of the sensor loops, you check for a different resistance if the Fenwal unit is installed than if the BECO unit is installed. The higher the alarm threshold, the higher the resistance for which you check.
B. A false alarm is usually due to a direct short to ground in the power wire of a heat sensing loop. If trouble shooting per the chart isolates the trouble to the heat sensing loop or airplane wiring, check for improperly installed electrical connectors; moisture may have entered at the improper connection. Remove moisture by blowing out connectors with dry nitrogen.
C. Prior to making any tests, equivalent test connectors (wire end fittings) should be installed at the receptacle. The test connector should have exposed contact points or wires to attach to or touch test probes. The test connector protects airplane wire from the possibility of arcing or other damage and provides position contact for attachment of test equipment.
NOTE: If precautions are not taken, occasionally an oversized test probe may be forced into the sockets of a sensing element, this may spread the contacts and prevent the mating pin from making contact in the sleeve.
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Feb 01/96 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 26-18-0 Page 101
A90537 A90546 A90550
Left Wing-Body Overheat Troubleshooting Diagram 500
26-18-0 Figure 101 (Sheet 1) May 01/99
Page 102
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
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