Sorry to post about this every month, but I have some potentially additional information about the terrible CPU/board failure of the L2013-2015 A1398 boards.
I replaced two customer boards this week with this issue. When inspecting the boards, I found that U7310 had been replaced on both. There was no sign of liquid to that area (no discolored cap ends or anything), and neither was shorted, but both had definitely been replaced. They were replaced pretty cleanly as well, but looked to have been done by Apple (not perfect, but good enough, small amount of flux, a few pins not "perfect", etc). Both boards had the same CPU failure; both had issues coming out of deep sleep/hibernation (i.e. I would leave them overnight, open the unit and fans would be running high and no video, etc). I'm going to go through the pile of boards with the issue and see how many have had U7310 replaced.
Knowing this is a vcore issue, could it be that one of the regulators/power supplies (U7310/20/30) is failing, which prevents vcore from recovering/stabilizing? I know that it's possible these had s5_hs_computing shorted to ground, but knowing that kills the CPU so often (90%+), it would seem odd that both "survived" it well enough to be sold as refurbished by Apple (wouldn't put it past them, though). Additionally, there was zero sign of liquid at all--no discolored caps like you sometimes see when liquid touches there, etc.
To add a bit to this: I repaired a third 00138 board this week that DID have a tiny spot of liquid to U7310. Expecting the CPU to be dead, I did it with low hopes, but surprisingly the board powered right up and passed diagnostics. It ran Heaven for ~1 hour, at which point I closed the unit for the night. Came back the next morning and it, too, had high fans and no video...which makes me wonder if the U7310 I had pulled (from a board with the CPU issue, undoubtedly), might have been bad, and caused this board (that had survived a shorted s5_hs...) to develop the CPU issue? Most likely a huge coincidence, but could faulty U7310/20/30 chips be causing this whole issue? I know you, duke, have done WAY more testing on this than I'll ever hope to have time to do, but I did think it was interesting. I know the current thought is that there are open lines/traces inside the board, and that it isn't repairable. It's so painful telling retail-customers that this board is not repairable.
Just a thought, curious to hear your input.
I replaced two customer boards this week with this issue. When inspecting the boards, I found that U7310 had been replaced on both. There was no sign of liquid to that area (no discolored cap ends or anything), and neither was shorted, but both had definitely been replaced. They were replaced pretty cleanly as well, but looked to have been done by Apple (not perfect, but good enough, small amount of flux, a few pins not "perfect", etc). Both boards had the same CPU failure; both had issues coming out of deep sleep/hibernation (i.e. I would leave them overnight, open the unit and fans would be running high and no video, etc). I'm going to go through the pile of boards with the issue and see how many have had U7310 replaced.
Knowing this is a vcore issue, could it be that one of the regulators/power supplies (U7310/20/30) is failing, which prevents vcore from recovering/stabilizing? I know that it's possible these had s5_hs_computing shorted to ground, but knowing that kills the CPU so often (90%+), it would seem odd that both "survived" it well enough to be sold as refurbished by Apple (wouldn't put it past them, though). Additionally, there was zero sign of liquid at all--no discolored caps like you sometimes see when liquid touches there, etc.
To add a bit to this: I repaired a third 00138 board this week that DID have a tiny spot of liquid to U7310. Expecting the CPU to be dead, I did it with low hopes, but surprisingly the board powered right up and passed diagnostics. It ran Heaven for ~1 hour, at which point I closed the unit for the night. Came back the next morning and it, too, had high fans and no video...which makes me wonder if the U7310 I had pulled (from a board with the CPU issue, undoubtedly), might have been bad, and caused this board (that had survived a shorted s5_hs...) to develop the CPU issue? Most likely a huge coincidence, but could faulty U7310/20/30 chips be causing this whole issue? I know you, duke, have done WAY more testing on this than I'll ever hope to have time to do, but I did think it was interesting. I know the current thought is that there are open lines/traces inside the board, and that it isn't repairable. It's so painful telling retail-customers that this board is not repairable.
Just a thought, curious to hear your input.
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