08 Troubleshooting
The most common faults of PLC can be classified into three main categories: 1. Power failure; 2. I/O failure; 3. Communication failure. Wecon PLC consists of three boards：upper board(communication board), middle board(CORE board) and lower board(power board), so users can judge which board has the problem according to the fault.
Power failure
The power board supplies power to the above CORE board and light board. When there is a problem with the power board, some signals transmitted to the above board will have problems. Common PLC power failures are as follows:
| Number | Failure | Troubleshooting | Solution |
|---|---|---|---|
| 1 | The light does not light up when the power is turned on, and the PLC does not respond. | 1. It is possible that the 220V connection of the host is wrong, the power supply between the motherboards is not properly connected, or the pin header is damaged and soldered. 2. Use a multimeter to measure whether there is voltage between the 24V+ of the PLC and COM, if there is no voltage, the power board is faulty; 3. Use a multimeter to measure whether there are voltages of 24V and 5V at the BD interface on the PLC. If there is voltage, the LED or core board may be damaged; if 24V is normal, but 5V is not, there may be a problem with the DC conversion circuit of the power board； | When it is suspected to be the problem of the power board, user can replace the power board for confirmation. |
| 2 | PWR light flashes | 1. Use a multimeter to measure whether the PLC 24V power supply is abnormal (constantly changing). If this happens, it means that the 24V conversion circuit of the power supply board is faulty. 2. Generally, the flashing of PWR can eliminate the front-end problem of the AC power supply of the power board; | 1. Replace the power supply board to confirm whether it is the power supply board problem; 2. Observe whether the motherboard components are soldered incorrectly, or whether there is a diode soldering direction reversed 3. Use a multimeter to measure whether there is any problem with the output DC5V of the power board; |
| 3 | RUN light is off | 1. Use a multimeter to measure whether the 24V voltage and 5V voltage on the BD interface are normal when the PLC is powered on; 2. There may be a problem with the CORE board of the host, and confirm the replacement. | If the voltage of the power board is no problem, user need to replace the CORE board to confirm whether there is a problem with the CORE board. |
I/O failure
The input and output of PLC is the main function of use, and I/O point problems are often caused by improper use or process\individual device problems; Including how the customer uses it, whether the mount is in compliance, etc. are all causes that lead to I/O failures .
| Number | Failure | Troubleshooting | Solution |
|---|---|---|---|
| 1 | X point failure | 1. Use PLC software to detect X points that cannot be lit; 2. Connect PLC S/S to 24V, change multimeter to 20mA gear. The red test lead is on the X point of the fault, and the black test lead is on a Y point (the COMx corresponding to Y is connected to the COM terminal of the 24V voltage); 3.Use PLC software to control the on-off of the Y point(connected in step2) to check whether there is current on the multimeter. The high-speed input current is about 6.8mA, and the low-speed input current is about 4.7mA. | If no voltage is detected, the motherboard needs to be replaced for confirmation. |
| 2 | Y point failure | 1. All COMx of PLC are connected to COM; 2. Power on the PLC, use the buzzer of the multimeter, pen one test lead on COM, and the other on the Y that needs to be detected, and observe whether the buzzer sounds when the lamp board Y is not lit. ; | The normal situation is that the buzzer will beep when Y is turned on, and there will be no buzzer when it is turned off, or the Y point needs to be replaced. |
Communication failure
The main communication ports of PLC are two serial ports, one S terminal serial port, and one USB port. The specific troubleshooting methods for communication faults are as follows：
| Number | Failure | Troubleshooting | Solution |
|---|---|---|---|
| 1 | USB not recognized | 1. For PLCs used for a long time, it may be caused by the oxidation of the USB port or poor contact in other places; 2. For the new PLC, it may be a USB problem or an inconsistent software version; | If no voltage is detected, the motherboard needs to be replaced for confirmation. |
| 2 | 485 port cannot communicate | 1. Power on the PLC, observe the transceiver communication lights on the side of the serial port terminal, you can preliminarily determine which serial port has the problem of receiving/transmitting; 2. Check whether the serial port transceiver ± data cable is connected incorrectly, and whether the ground wire is reliably connected; 3. Determine whether there is a poor connection between the upper board and the CORE board; | Replace the upper board for confirmation |
| 3 | BAT light on | 1. Caused by insufficient battery power; 2. The BAT light circuit is faulty, causing the CPU to receive the wrong signal, causing the BAT light to light up | 1. Change battery to check if it is solved; 2. Check whether there is poor contact between the upper board and the CORE board； 3. Replace the upper board and the CORE board respectively for troubleshooting. |
| 4 | ERR light flashes | Could be a CORE board firmware issue | Replace the CORE board for confirmation. |
| 5 | The expansion module/BD module cannot communicate with the host | 1. The module may be faulty, including frequent hot swapping during use. 2. It may be that the host fault needs to be clearly located | 1. Observe whether the expansion module itself is damaged; 2. Control variables to determine whether it is a module problem or a host problem; 3. If the communication is abnormal due to the host, replace the upper board and the CORE board respectively to confirm; 4. If it is the module that causes the communication abnormality, it needs to be analyzed and checked separately; |
| 6 | RUN and ERR flash in same frequency | 1. Unstable power supply 2. Firmware issue | 1. Measure the power input and ensure that the power supply is stable. 2. Replace the core board(middle board) and check. |