You can check each of the 6 PCIe wires for hot.
If you find one that is NOT hot when all others are it is the problem.
If you find one that is NOT hot when all others are it is the problem.
If you find one that is NOT hot when all others are it is the problem.

You need all 6 PCIe wires working for 'safe' operation.
They should all be same temperature.

Best to change the PCIe cable if you have ONE cool wire in a hot cable.
You could also inspect the cable and look for wires that are not pushed all the way into the plastic connector housing.
If it is a modular PSU look at PSU end also.
Be sure connectors are installed all the way.
PUSH on wires when connecting, PULL on plastic housing when disconnecting.

Most melted PCIe cables I have ever seen were caused by a failure in one of the 6 wires.
If you ever find only 2 melted it is because they did not survive doing work for bad wire.
They tried but failed.
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You might just have a ASIC that uses more power.

YMMV