Have reset SMC/NVRAM. Not sure what's going on. It's fine if I use it normally, but if I walk away from it and come back a few minutes later it'll be turned off, even if I set it to not sleep and the display to stay on with a screensaver. ... Hardware diagnostic with "D" says it's fine? Anyone run into this? Doesn't matter if I'm on battery power or AC. — The logic board was replaced two years ago and the battery/top-case 1 year ago, but I'm now out of warranty.