So bought a dead A1990 board off eBay (820-01814). Don't know the history other than it's iCloud locked and not working. So hopes weren't high.
Board is relatively clean, appears to be some evidence of some type of cleaning in some areas but no rework evident. Anyway, in summary PPBUS_G3H has a 2 ohm impedance to deck, and this was traced to the same on PP3V3_G3H_RTC. U6960 (TPS62180) had shorted so its had the full 12V dumped on the 3.3V line. PPBUS short was gone after U6960 removed and isolated the low resistance to after R6934/R6935 (no output filter cap shorted unfortunately). Removed U3200 (CD3215) and resistance went up to 9 ohms. Was hoping that one may have failed and saved the others but all 4 CD3215's were done and dusted.
So now have 60 ohms on the PP3V3_G3H_RTC rail, which is still too low and likely other damaged components on this rail. Some are minor but we do have the SSD and PMU power regulators being fed by this. No data sheets so don't know if 12V input is excessive or not.
So in a nutshell, just wondering if anyone else who have had a shorted 3V3 RTC regulator on these T2 MAC's whether this is a recoverable situation or not? I have another T2 board from a 2018 MAC that I got dead, where it seems the last repair fixed the 3.3V regulator and stopped after that. 13 ohms to ground on this rail so it doesn't seem like a one off.
Board is relatively clean, appears to be some evidence of some type of cleaning in some areas but no rework evident. Anyway, in summary PPBUS_G3H has a 2 ohm impedance to deck, and this was traced to the same on PP3V3_G3H_RTC. U6960 (TPS62180) had shorted so its had the full 12V dumped on the 3.3V line. PPBUS short was gone after U6960 removed and isolated the low resistance to after R6934/R6935 (no output filter cap shorted unfortunately). Removed U3200 (CD3215) and resistance went up to 9 ohms. Was hoping that one may have failed and saved the others but all 4 CD3215's were done and dusted.
So now have 60 ohms on the PP3V3_G3H_RTC rail, which is still too low and likely other damaged components on this rail. Some are minor but we do have the SSD and PMU power regulators being fed by this. No data sheets so don't know if 12V input is excessive or not.
So in a nutshell, just wondering if anyone else who have had a shorted 3V3 RTC regulator on these T2 MAC's whether this is a recoverable situation or not? I have another T2 board from a 2018 MAC that I got dead, where it seems the last repair fixed the 3.3V regulator and stopped after that. 13 ohms to ground on this rail so it doesn't seem like a one off.
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