Hi Dan, i'm troubleshooting a MPBr 15" Late 2013 from which i suspect a faulty IO-board connector. After a SMC-reset the USB-port works, SD card reader doesn't (haven't tried HDMI). Also randomly the Flex cable gets hot to the touch (which indicates shorting?). I've noticed that the metal shielding on the IO-board is loose on one side, this is used for grounding i presume? Can this be the cause of the issues i'm seeing?
Before i'm ordering all the parts you've mentioned i'd like to pinpoint it a bit more. The issues started after i've replaced the 7-year old battery. I haven't checked the IO-board datacable on the Logicboard side. Should i check this? Does the Flexcable go bad as easily as the datacable does?