MAINTENANCE DOCUMENTS - FIM - MAINTENANCE MESSAGE INDEX
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MAINTENANCE DOCUMENTS -- FIM - FIM TASKS General
FIM tasks have the procedures to find and correct faults. The tasks are grouped at the sub-subsystem level. For example, all sub-subsystem 27-31 tasks are in a group. These tasks are in numerical order by task number.
The task identifier is the sub-subsystem number, the word TASK, and a three digit number.
Each FIM task assumes that the cause of the fault is a single failure.
FIM Task Structure
Each FIM task has some or all of these paragraphs:
-Task title with task number
-Task description
- Possible causes 
- Circuit breakers 
- Related data 
- Initial evaluation 

-Fault isolation steps.
These are the assumed conditions at the start of the task:
-External electrical power is on -Hydraulic power and pneumatic power are off -Engines are shut down -Circuit breakers for the system are closed
737-600/700/800/900 TRAINING MANUAL
-No equipment in the system is deactivated.
The task has an initial evaluation paragraph that tells you if the fault is intermittent.
After the initial evaluation paragraph, the task has several steps. The steps may use several different paths. When you are at the end of a path, that task says that you corrected the fault.
Training Information Point
When a step in a FIM task says to do a wiring check, these are the types of checks you must do for the specified pins:
-Continuity from contact to contact
-Shorts between the contacts
-Shorts from each contact to ground.
A step in a FIM task may ask you to do a task in the AMM. After you do the AMM task, you must go back to the FIM and complete the FIM task.
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737-600/700/800/900 TRAINING MANUAL

TASK TITLE AND TASK NUMBER
MAINTENANCE MESSAGE

TASK DESCRIPTION
POSSIBLE CAUSES
CIRCUIT BREAKERS
RELATED DATA
INITIAL EVALUATION PARAGRAPH

FAULT ISOLATION MANUAL
814.  Start Power Unit Shows Start System INOP - Fault Isolation

A. This task is for maintenance message : 49-41253
B. Description

(1)
This task is for this maintenance message:

(a) 49-41253 START POWER UNIT SHOWS START SYSTEM INOP

(2)
During an APU start cycle, the start power unit uses ac power first (if available) or dc power from the airplane battery and charges this power to 270VDC. This power is supplied to the start converter unit. The ac/dc converter and dc/dc converter in the start power unit use monitoring circuits to do a check for correct operation. This fault is set when on of the two converters is defective.

(3)
The APU fault light on the P5 forward overhead panel can show for this maintenance message.

C. Possible Causes

(1)
Start Power Unit, M1850
(AMM TASK 49-41-71-000-801, P401)

(2)
Voltage problem between the APU START CONV circuit breaker and the start power unit, M1850.

D. Circuit Breakers

(1) These are the primary circuit breakers related to the fault:
(a)
 Battery Shield, J9:
1) 9Z99 BATTERY CHARGER

(b)
 Circuit Breaker Panel, P6-4: 1) 6A14 AUX POWER UNIT CONT 2) 6B14 AUX POWER UNIT SCU FAN POWER

(c)
 Power Distribution Panel Number 1, P91: 1) 91G1 APU START CONV

E. Related Data

(1)
Simplified Schmatic (Fig 302)

(2)
WDM 49-41-11

F. Initial Evaluation

(1)
Do this task: APU BITE procedures (FIM 49-60 TASK 801.)

(a)
If the CDU display shows this maintenance message on the CURRENT STATUS page, then do the Fault Isolation Procedure below.

(b)
If the CDU display does not show this maintenance message on the CURRENT STATUS page, then there was an intermittent fault.

G. Fault Isolation Procedure

(1) Do these steps to replace the start power unit, M1850:
ISOLATION STEPS

(a)
 Make sure the APU master switch is OFF.

(b)
 Replace the start power unit, M1850. These are the tasks: Start Power Unit Removal (AMM TASK 49-41-71-000-801 p401), Start Power Unit Installation (AMM TASK 49-41-71-400-801 p401),

(c)
 Do this task: APU BITE procedure (FIM 49-60 TASK 801.)

(d)
 Set the APU master switch to the ON position.

(e)
 Look at the CURRENT STATUS page on the CDU display to see if this maintenance message shows.
　
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