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MELSEC-Q
10 TROUBLESHOOTING
10.3 Troubleshooting by Symptom
This following shows troubleshooting of trouble generated during communications
between the Q series C24 and external device according to the trouble symptom.
When trouble occurs, first confirm the status of the Q series C24 and check the
relevant item in the table below.
Protocol
Symptom Symptom description
Dedicated
Non
procedure
Bidirec-
tional
Reference section
• "RUN" LED turned off. Section 10.3.1
• "RD" does not blink even through an external device
is transmitting a message.
Section 10.3.2
• An external device transmitted a message and "RD"
blinked, but the Q series C24 did not return a
response message.
Section 10.3.3
• An external device transmitted a message and "RD"
blinked, but the Q series C24 did not turn ON the
read request.
Section 10.3.4
LED turns on/off (check according to
Section 4.3)
• ERR. LED turns on.
Section 10.3.20
• The "NAK" was turned ON. Section 10.3.5
• The "C/N" was turned ON.
Section 10.3.6
• The "P/S" was turned ON. Section 10.3.7
• The "PRO" was turned ON.
Section 10.3.8
• The "SIO" was turned ON. Section 10.3.9
• The "CH1. ERR. " or "CH2. ERR. " was turned ON.
Section 10.3.10
• Communications are intermittently established and
lost.
Section 10.3.11
• Data that cannot be decoded was transmitted and
received.
Section 10.3.12
Communication errors occurred
(check according to Section 10.1.1)
• Whether the cause of the communications error is in
the Q series C24 or the external device is unknown.
Section 10.3.13
• Cannot communicate via modem.
Section 10.3.14
Cannot communicate via modem
(
1
)
• Cannot communicate with ISDN sub-address. Section 10.3.15
• Does not operate in the cycle time designated in the
constant cycle transmission setting.
Section 10.3.16
The PLC CPU monitoring function
does not operate in the designated
cycle time.
• Does not operate in the cycle time designated in
condition agreement transmission setting.
Section 10.3.17
Cannot receive by an interrupt
program
• Cannot receive data.
Section 10.3.17
Cannot perform initial setting
• Cannot write setting value in flash ROM of the Q
series C24.
Section 10.3.19
1 If an error occurs while performing data exchange using the modem function
described in User's Manual (Application) Chapter 3, first check the following items
and confirm whether or not the error is caused by the modem/TA connection.
If an error relating to the modem function is occurring, perform necessary
corrective actions for each cause according to the reference sections given below:
• Check the ON/OFF status of current I/O signals of the Q series C24.
• Check the storage status for error codes related to the modem function. (See
Sections 10.2.3.)
• Check the ON/OFF status of the DR terminal of the modem/TA. (See the
manual for the modem/TA.)