840Dsl, LEDs on MCP are freezing

[wendaiyu]

Hi, guys, we have a 840Dsl milling machine. Since one week ago, there is a small issue on it: LEDs on MCP are freezing after pressing Reset (PO) on the HMI. We have to shut down the main power and power up, then MCP works well. When LEDs were freeing, we checked the I/Os on MCP via PLC. They were all functional. E.g. I0.0 is for “JOG” on MCP and Q0.0 is for its LED. I0.3 for “AUTO” and Q0.3 for its LED. When we pressed “JOG” button, I0.0 and Q0.0 are both 1. And when we pressed “AUTO”, I0.3 and Q0.3 are both ON. But the LEDs still remain the same as the last status before we press Reset (PO) on the HMI. We replaced a new MCP, but the same problem. We found that for normal MCP, if it has communication failure with PLC, all LEDs are flashing. But in our case, even the HMI showed us communication failed, the LEDs were still freezing. We checked I/Os and changed MCP, so we think the communication cable or 24V power may be defective. Could you give us a hand to figure it out ? Thanks a lot.