No Access to System BITEs from the MCDU

TASK 31-32-00-810-938-A
No Access to System BITEs from the MCDU

1. Possible Causes

CFDIU [1TW]
computer on the output bus

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 31-32-00-740-002	BITE Test of the Centralized Fault Display Interface Unit (CFDIU)
ASM 313202
ASM 313203
ASM 313204
ASM 313205
AMM 31-32-34-000-001	Removal of the CFDIU
AMM 31-32-34-400-001	Installation of the CFDIU

3. Fault Confirmation
Subtask 31-32-00-865-170-A

A. Table of the circuit breakers used in this procedure:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
121VU	CFDS/CFDIU/SPLY	2TW	J18
121VU	CFDS/CFDIU/BACK/UP	8TW	J17

Subtask 31-32-00-710-065-A

B. Test
(1) Reset of the CFDIU

NOTE: Open the circuit breakers for some seconds before you close them.

(a) Open this(these) circuit breaker(s):
1 2TW
2 8TW
(b) Close this(these) circuit breaker(s):
1 2TW
2 8TW
(2) Do the BITE test of the CFDIU for the power up test result AMM 31-32-00-740-002.

4. Fault Isolation
Subtask 31-32-00-810-189-A

A. If the fault symptom is identified by:

no access to system BITEs from the MCDU

and
power up test result not OK

(1) Make a record of the CFDS maintenance fault message.
(2) Do the trouble shooting procedure related to the CFDS fault message.

Subtask 31-32-00-810-190-A

B. If the fault symptom is identified by:

no access to system BITEs from the MCDU

and
power up test result: TEST OK

(1) Check of the CFDIU and the electrical connector for correct condition.
(a) Remove the CFDIU [1TW] AMM 31-32-34-000-001.
(b) Install a new CFDIU [1TW] AMM 31-32-34-400-001.
(2) If the fault continues:
(a) Use the Aircraft Schematic Manual (ASM) to find the number (1, 2, 3 or 4) of the CFDIU output bus related to the system BITEs which do not operate (each computer is linked to an output bus number).
(b) Do a check and repair the wiring from the related CFDIU output bus to the first terminal block (only bus 1, 2, 3 or 4):
1 For output bus 1, from connector AA/2B, 2C to the first terminal block ASM 313202.
2 For output bus 2, from connector AB/2H, 2J to the first terminal block ASM 313203.
3 For output bus 3, from connector AA/11F, 11G to the first terminal block ASM 313204.
4 For output bus 4, from connector AB/11D, 11E to the first terminal block ASM 313205.
(3) If the fault continues:
(a) Remove all the computers connected to the CFDIU output bus (1, 2, 3 or 4) related to the system BITEs which do not operate (each computer is linked to an output bus number)

NOTE: The list of computers related to each CFDIU output bus is given in the Aircraft Schematic Manual (ASM).

(b) Check of the CFDIU output bus wiring and each computer on the output bus .
1 Do a check and repair the wiring for one computer on the output bus (only bus 1, 2, 3 or 4):

NOTE: If the POST FLIGHT REPORT (PFR) gives a CFDS fault message(s) of the type "NO DATA FROM CFDIU", first do a check of the line related to the computer which is the source of this maintenance message.

a For output bus 1, from connector AA/2B, 2C to the connector of the computer ASM 313202.
b For output bus 2, from connector AB/2H, 2J to the connector of the computer ASM 313203.
c For output bus 3, from connector AA/11F, 11G to the connector of the computer ASM 313204.
d For output bus 4, from connector AB/11D, 11E to the connector of the computer ASM 313205.
2 If the wiring to this computer is correct, install the computer.
3 Do a check for access to the system BITE of this computer.
a If the access to the BITE is not possible

replace the defective computer
install all the other computers that you removed.

b If the access to the BITE is possible

do the same checks (output bus wiring and computer BITE) until you find the defective line or computer.

Subtask 31-32-00-710-066-A

C. Test
(1) Make sure that all the system BITEs are available.

NOTE: The list of computers related to each CFDIU output bus is given in the Aircraft Schematic Manual (ASM).

(2) Do the BITE test of the CFDIU AMM 31-32-00-740-002.

[Rev.8 from Aug 2018] 2026.04.04 04:29:59 UTC