Discussion on Mitsubishi PLC repair and fault diagnosis

Mitsubishi PLC repair:

PLC repair and fault Mitsubishi align="left">  

PLC repair and fault Mitsubishi align="left"> Maintenance methods: open the machine check, found the power to burn, after bridge rectification filtering electrolytic capacitor has blasted fuse has burned black, using a multimeter to check, blasted the filter capacitor has a short circuit. The fuse is disconnected, one by one check other elements not found to have burned out. After replacing the fuse and filtering electrolytic capacitor energized, the measured power supply is normal, the whole machines installed, after power supply indicating lamp is bright, the input point and the common end of the short circuit, input bright lighting, the lighting output corresponding equally bright. Use the system test platform to test and confirm all normal.

Fault diagnosis for PLC:

All kinds of brand PLC have self diagnostic function, when the PLC is abnormal, it should make full use of its self diagnostic function to analyze the causes of failure. When the PLC when an exception occurs, first check the power supply voltage, PLC and I / O terminal screws and the connector is loose, and there is no other abnormalities. And then according to the basic unit of the PLC set up a variety of LED's indicator light condition, to check the PLC itself and the outside is no exception. When an error occurs, the value of one of the 8009, 8060~8068, is written into the special data register D8004, assuming that the content of the D8004 is 8064, and the error code is known by viewing the contents of the D8064. The actual error associated with the error code. See the error code table of the PLC use manual.

MITSUBISHI FX series PLC as an example, to illustrate the status of the LED based on the PLC indicator to diagnose the cause of the failure of the method.

1.       power indicator ([POWER]LED instructions)

As to the Mitsubishi PLC basic unit of power supply, the basic unit is disposed on the surface of the [POWER]LED indicator light exhibit of lanterns. If the power supply is not on the [POWER]LED indicator light, please confirm the power supply connection. In addition, if the same power source has a driver, please confirm that there is no load or short-circuit current. If it is not the above reasons, it is possible that the PLC mixed with conductive foreign body or other unusual circumstances, so that the basic unit of the fuse fuse, this time can be resolved by replacing the fuse.

2.       error indication ([EPROR]LED flash)

When the program syntax errors (such as the timer or counter to set the constant, etc.), or have abnormal noise, electrical foreign body mixed with other reasons and cause the contents of the program memory changes, [EPROR]LED will flash, MITSUBISHI PLC in the STOP state, while the output is OFF. In this case, the procedure should be checked whether there is a mistake, check whether there is no conductive material mixed with high intensity noise source.

3.       error indication ([EPROR]LED lights)

Due to the impact of the MITSUBISHI PLC internal mixed with electrical or external abnormal noise, resulting in a CPU control or operation cycle of more than 200ms, the WDT error, [EPROR]LED lights, PLC in STOP, while the output is OFF. At this point can be power reset, if the PLC return to normal, please check whether there is abnormal noise source and electrical conductivity of the foreign body into the case. In addition, please check the grounding of the PLC to meet the requirements. Check process if there is a change of [EPROR]LED light, please check the program. If [EPROR]LED is still in the light of the lamp, please make sure that the program's operation cycle is too long (to monitor the maximum scan time of D8012). If all the checks are carried out, the [EPROR]LED light status is still not released, the PLC should be considered in a certain kind of failure, please contact the technical service providers.

4.       input instructions

Regardless of whether the input unit of the LED lamp is on or off, please check whether the input signal switch is indeed in the ON or OFF state. If the input switch of the rated current capacity is too large or due to oil intrusion and other reasons, prone to contact. When the input switch with the LED lamp on the resistance in parallel, even if the input switch OFF but the parallel circuit is still on, can still be the input of the MITSUBISHI FX series PLC. If the use of optical sensors and other input devices, due to the light emitting / receiving the light parts of the dirt, etc., causing the sensitivity changes, there may not be fully into the ON state. ON and OFF input can not be received in a short period of time than the MITSUBISHI FX2N series PLC. If the input terminal is applied at different voltage, the input circuit will be damaged.

5.       output indicates

Regardless of the output unit of the LED lamp is bright or off, if the load can not be carried out ON or OFF, mainly due to overload, load short-circuit or the impact of capacity load current, etc., causing the relay output contact adhesive, or contact surface is not good cause contact.