Panasonic KX-F900 Service Manual page 39

I KX-F900
(Cause and Countermeasure)
(Cause A)
When the training signal is transmitted from FAX1 during the communication procedure at the time of transmission from
FAX1 to FAX2, there is a delay until the echo canceler operates and $1 is closed, so that a part of the head of the training
signal may drop out, normal reception by FAX2 may not be possible, and transmission may not be started.
(Cou ntermeasu re A)
When the international line mode becomes ON service mode (code No. 521), a dummy signal is attached to the head of
the training signal to prevent this problem. As this normally is ON, it is necessary to reconfirm that this has not becomes
OFF. When the international mode is switched OFF, the transmission side will try the training signal three times at each
speed (9600BPS, 4800BPS and 2400BPS), and in case of NG, it will drop the speed by one rank (fall-back). When the in-
ternational mode is switched ON, each speed will be tried only twice. In other words, the slower speed with fewer errors
are reached more easily. This is done as the line conditions may deteriorate and the picture may be disturbed more easily
during communication in case of international lines or long distance communication, even when the training has been OK.
The default value is ON as preference is given to clearer pictures rather than speed.
(Cause B)
The echo canceler operation is stopped with a signal of 2100Hz (i.e. $1 and $2 become ON).
Accordingly, when FAX1 has executed automatic reception, a CED signal is output, and if this signal should be 2100Hz,
$1 and $2 will become ON. Then the echo of the DIS signal output afterwards may be received and FAX1 may execute
erroneous operation, preventing start of communication.
(Countermeasure B)
In service mode, the CED signal frequency is set to 1100 Hz (code No.520) or the time setting between the CED signal
and the DIS signal is set from 75msec to 500msec in service mode (code No.593). This is done because the echo can-
celer operation stop mode is cancelled with an interval of 250msec or more.
(Cause C)
KX-F900 shall be assumed for FAX1 and a set of a different company shall be assumed for FAX2.
In case of transmission from the KX-F900 to FAX2, FAX2 executes automatic reception and transmits a CED signal (2100
Hz), followed by a DIS signal. As here the echo cancelers stops as described in cause B, the echo of the DIS signal re-
turns to FAX2. On the other hand, the KX-F900 detects the DIS signal and transmits a DCS signal. In other words, it is
possible that the echo of the DIS signal and the DCS signal transmitted from the KX-F900 reach FAX2 one after the other,
FAX2 executes erroneous detection, and communication are not started.
(Countermeasure C)
When international DIS detection setting is made effective in service mode (code No.594), the KX-F900 does not respond
to the first DIS signal and returns a DCS signal only for the second DIS signal.
In other words, there is an interval of 250msec between transmission of the first and the second DIS signal, so that the
echo cancelers operation recovers and no echo is generated for the second DIS signal.
Note:
When the other FAX does not respond with a DCS signal after DIS signal transmission, the DIS signal is transmitted three
times for trial.
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