Turns out there is a ribbon connecting the SATA daughter-board and the motherboard on the Asus R556 series laptops which is faulty. There are two fixes; reflow the traces at both ends of the ribbon (it’s easy to identify, as it crosses the HDD caddy), or purchase a new ribbon, daughter board and ribbon connector (for the motherboard interface). [br]
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Personally, I am inclined to agree with you, ‘Planned Self-Termination’. :/[br]
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….and Asus used to be so good too. :(