TM 11-7025-221-20
2-13. ALARMS BUS Troubleshooting.
Perform the troubleshooting procedures in this paragraph when directed by the TD-1337(V)/G troubleshooting
procedures in paragraph 2-9.
a. Description of Problem. Data are exchanged between the microprocessor and the other cards via
an eight-bit hi-directional data bus. At regular intervals, a test is automatically performed on the data bus.
The test consists of writing data to and reading that data from unused areas of memory on NVM card
A9 and display card A23A1 .Failure of this test will cause the ALARMS BUS indicator to light. There are
four cards (A9, A11, A22, and A23A1 ) directly involved in conduct of the test. The other cards connected
to the data bus can cause a test failure if they have a fault that pulls one or more bits of the data
bus low.
b. Description of Troubleshooting. The procedures in the flowchart first direct you to lift, one-at-a-time,
those cards not directly involved in conduct of the test. If one of these cards is faulty, a normal power
on display will occur when faulty card is lifted and POWER CB is set to ON. If none of these cards
are faulty (normal power on display does not occur when ail designated cards are lifted), they are seated
(installed) in the card file. Next, YOU are directed to replace, one-at-a-time, each of the four cards directly
involved with conduct of the bus test.
c. Use of Troubleshooting Flowchart. Go to the START entry in the flowchart. Perform the actions
as directed until the fault is isolated and corrected. If necessary, refer to the plug-in card replacement
instructions in paragraph 2-18 and the display card replacement instructions in paragraph 2-22. When you
are directed to lift a card, extend the two card ejector handles on the edge of the card. This action
lifts the card so that the card edge connector is disconnected from the connector pins in the card file.
It is not necessary to completely lift the card out of the card file. If none of the replaceable assemblies
are faulty, the flowchart will direct you to call next higher level of maintenance.
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