Mitsubishi MELSEC PLC Troubleshooting

My Mitsubishi MELSEC PLC suddenly stopped responding after running flawlessly for a while, and I need a seasoned PLC specialist to pinpoint the fault and guide me to a reliable fix. I have already uploaded close-up photos of the CPU rack, indicator LEDs, and wiring, along with a short video that shows the power-up sequence and current status lights, so you can see exactly what I’m seeing.

The controller shows no error codes on the front display, yet I can’t establish any communication through GX Works or via the HMI. No firmware, software, or hardware changes were performed prior to the failure, and the remaining plant equipment is operating normally, so we’re dealing with a true intermittent-to-dead scenario isolated to this unit.

What I need from you:
• A step-by-step diagnostic plan based on the evidence provided (and any clarification you request).
• An analysis of the most probable root cause—whether it’s power supply, CPU fault, backplane, I/O module, or field wiring.
• Clear remediation instructions that I can execute on site; if a component swap is required, specify exact part numbers.
• Confirmation tests I should run with GX Works (or your preferred tool) to verify the PLC is fully responsive again.

Acceptance criteria: once your recommendations are applied, I should be able to connect to the PLC, download/upload the program without timeouts, and see steady RUN/COMM LEDs with the machine cycling normally.

If you’ve dealt with MELSEC series faults before and can walk me through this quickly—possibly over a screenshare—let’s get started right away.