31-42-00
 ú ú 04 Page 15 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 (12) Built-in Test Equipment (BITE)
 (a)  
A BITE facility is incorporated in the engine displays, and will test the indicator for confidence level. The BITE facility is inhibited whenever an engine is running.

 (b)  
An unmarked recessed pushbutton is located in the bottom of the front bezel. Single operation of this button (holding button depressed) enables an "on ground" BITE sequence provided that both N1 displays indicate less than 10% rpm, otherwise BITE is inhibited.

 (c)  
The BITE sequence tests all functions (that are practical) within the instrument and in the event of failures displays fault codes on the counter displays per Table A. It also tests each parameter throughout its range and at preset parameter values.

 (d)  
On unit "power up" the same sequence of tests are carried out prior to the displays being illuminated and if a fault condition is detected the relevant display remains blank. Pressing and holding the "on ground" BITE button causes the detected fault code to be displayed on the appropriate numeric counter; when BITE button is released the display returns to normal operation.

 Table A: Primary Display Fault Codes
 ~............................................................ | Fault | Code | Module | .............................................................. | Prom Check Sum | ROM | FF, N1, N2, EGT | .............................................................. | RAM Check | RAM | FF, N1, N2, EGT | .............................................................. | Frequency/Digital Converter | FDC | N1, N2, EGT and FF | .............................................................. | Engine Identity Inputs | ENG | N1, N2, and EGT | .............................................................. | Power Monitor | PWR | N1, N2, EGT and FF | .............................................................. | Maintenance Module Fault | MMF | Fuel Flow (left) | .............................................................. | Real Time Clock | RTC | Fuel Flow | .............................................................. | Exceedance RAM Full | ERF | Fuel Flow (left) | .............................................................. | A/D Converter | A/D | N1 | .............................................................. | ARINC Receiver | ARF | Fuel Flow | .............................................................. | Processor | .P | N1, N2, EGT and FF | 2.............................…........….....................1
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 31-42-00
 ú ú 04 Page 16 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (13)
 Exceedance Data Recording and Storage

 (a)  
The highest exceedance value and the duration of the exceedances, since power up, will be recorded for actual N1, N2 and EGT for both engines in volatile RAM by the individual processors. During exceedance/Abnoramal Start conditions all parameter values including fuel flow for that engine will be stored in non-volatile RAM.

 (b)  
Maintenance module storage begins with an exceedance on N1, N2 or EGT or upon the detection of an Abnoram Start condition. When this occurs all four parameters for the engine in addition to the airplanes air/ground condition and the Abnormal Start condition status will be recorded during the total time of the exceedance/Abnormal Start condition. Data points of actual parameter values will be taken at 1.2 second intervals.

 (c)  
Up to ten minutes of exceedance data can be stored before the memory will be full. When the exceedance memory is full, an ERF (Exceedance RAM Full) message will be displayed on the left fuel flow counter readout during BITE. The presence of this message does not affect the operation of the EIS display unit, and the exceedance data storage will continue to function properly; however, the new data will start to overwrite the oldest data. The ERF message warns maintenace personnel that the exceedance memory should be read and then cleared.
　
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