Nokia N900 Service Manual page 120

Using the audio self test
The audio self test can be used to quickly determine if the left and right audio paths are intact.
The left and right audio connectivity self test process performs the following steps:
1 Measure and store silence.
2 Inject 1KHz tone (left or right) to give 75KHz deviation. Measure and store.
3 Inject same tone on both left and right analogue audio inputs. Measure and store. Compare result from
(2) with result from (1). If the delta is NOT more than a specified threshold level then fail. This would
indicate that the selected channel is open circuit. If an over deviation indication is detected on (2), then
the audio channels must be shorted together. This is a fail condition. For (3), a returned value of zero is
expected. This indicates that there is an over deviation condition which in turn indicates that the 'other'
audio input channel is connected correctly.
If on (3) there is no over deviation response, then the 'other' channel must be open circuit at some point in
the audio path. This is a fail condition.
The table shows the truth table for the left and right audio self test.
LEFT RIGHT
0 0
1 0
1 0
1 0
0 1
0 1
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Figure 23 FMTx panel in action
Table 13 Left and right audio self test truth table
ASQ Condition
0
0
1
2
X
X
COMPANY CONFIDENTIAL
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Comment
SILENCE
OPEN/SHORT
OK
SHORT
Don't Care
Don't Care
RX-51
BB Troubleshooting
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