10 TROUBLESHOOTING

10.3 Troubleshooting by Symptom

MELSEC-Q

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

Bidirec-

Reference section

 

 

 

procedure

tional

 

 

• "RUN" LED turned off.

 

 

 

Section 10.3.1

 

• "RD" does not blink even through an external device

 

 

 

Section 10.3.2

 

 

is transmitting a message.

 

 

 

 

 

 

 

 

 

 

• An external device transmitted a message and "RD"

 

 

 

 

LED turns on/off (check according to

 

blinked, but the Q series C24 did not return a

 

 

 

Section 10.3.3

Section 4.3)

 

response message.

 

 

 

 

 

• An external device transmitted a message and "RD"

 

 

 

 

 

 

blinked, but the Q series C24 did not turn ON the

 

 

 

Section 10.3.4

 

 

read request.

 

 

 

 

 

•

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

Communication errors occurred

•

The "CH1. ERR. " or "CH2. ERR. " was turned ON.

 

 

 

Section 10.3.10

(check according to Section 10.1.1)

•

Communications are intermittently established and

 

 

 

Section 10.3.11

 

 

lost.

 

 

 

 

 

 

 

 

 

 

• Data that cannot be decoded was transmitted and

 

 

 

Section 10.3.12

 

 

received.

 

 

 

 

 

 

 

 

 

 

• Whether the cause of the communications error is in

 

 

 

Section 10.3.13

 

 

the Q series C24 or the external device is unknown.

 

 

 

 

 

 

 

 

 

Cannot communicate via modem

•

Cannot communicate via modem.

 

 

 

Section 10.3.14

( 1)

•

Cannot communicate with ISDN sub-address.

 

 

 

Section 10.3.15

The PLC CPU monitoring function

• Does not operate in the cycle time designated in the

 

 

 

Section 10.3.16

 

constant cycle transmission setting.

 

 

 

does not operate in the designated

 

 

 

 

 

• Does not operate in the cycle time designated in

 

 

 

 

cycle time.

 

 

 

Section 10.3.17

 

condition agreement transmission setting.

 

 

 

 

 

 

 

 

 

Cannot receive by an interrupt

•

Cannot receive data.

 

 

 

Section 10.3.17

program

 

 

 

 

 

 

 

 

 

Cannot perform initial setting

• Cannot write setting value in flash ROM of the Q

 

 

 

Section 10.3.19

 

series C24.

 

 

 

 

 

 

 

 

 

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.)

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