this is the summary of what we did. original problem was after cleaning board from spill: no power on, no light on magsafe3 charger. i have some limited soldiering experience like hdmi ports but this is my first time component chasing using openboardview and pdf file. it took me like several hours cause i didn't know what i was doing but the AI gave me summary of what we did. do you think it is correct? Im not smart enough to check chatgpt on this one.
🛠 MacBook Pro A2485 (M1) — No Power Troubleshooting Summary
Background
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Device: MacBook Pro A2485 (2021 M1)
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Issue: No power via any port (USB-C or MagSafe 3)
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Context: Logic board removed, carefully cleaned (including vinegar/QD electronic cleaner), and visually inspected. Charging port shows no LED. Known good charger used. I also cleaned the board very throughly with good old 99% isopropal like 2x with a microscope until it looked perfect and couldn't smell any other smell. but 0 ports got any 20v negotiation via fnb58 usb tester.
Tools Used
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FNB58 USB-C tester (verifies 20V negotiation)
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OpenBoardView with A2485 boardview file
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Owon SPM6103 meter/powersupply (also did diode testing)
🔍 Step-by-Step Troubleshooting
✅ USB-C/PPDCIN Input Verification
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Confirmed USB-C ports and MagSafe deliver ~5V at initial negotiation stage
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No 20V negotiation — power supply did not detect handshake
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Voltage measured at cap C5206 confirms PPDCIN_AON_CHGR_R is getting ~4.9V
✅ Power MOSFET Inspection (Q5240 / DB49AT)
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Identified Q5240 as a 14-pin dual N-channel MOSFET labeled
DB49AT, consistent with FDMD8800 (ON Semiconductor) (via pdf file) -
Pins 1–3 (PPVBAT_AON_CHGR_REG) show ~0.07V
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Gate pins (4 = Q3 gate, 12 = Q4 gate) show 0V
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Pins 7–11 (PHASE/LX) show <0.1V
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Diode-mode test showed reasonable values — not shorted per the meaning is per the ai:
| Pin Group | Behavior | Meaning |
|---|---|---|
| Pins 1–3, 13 (Source) | ~0.07 V | Extremely low — suggests rail is loaded or FET is leaky |
| Pin 4 (Gate Q3) | ~1.02 V (OK) | Gate appears healthy here |
| Pin 12 (Gate Q4) | ~0.54 V (too high) | Leaky or partially shorted gate |
| Pins 7–11 (Drain/Phase) | 0.5–0.54 V, bursts | Normal body diode behavior, but FET likely not switching |
| Pins 5, 6, 14 (GND) | ~0.0016 V (expected) | Ground plane is solidPin Group Behavior MeaningPins 1–3, 13 (Source) ~0.07 V Extremely low — suggests rail is loaded or FET is leakyPin 4 (Gate Q3) ~1.02 V (OK) Gate appears healthy herePin 12 (Gate Q4) ~0.54 V (too high) Leaky or partially shorted gatePins 7–11 (Drain/Phase) 0.5–0.54 V, bursts Normal body diode behavior, but FET likely not switchingPins 5, 6, 14 (GND) ~0.0016 V (expected) Ground plane is solid |
✅ Gate Drive Logic
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R5240 (likely pull-up to gate) shows 4.1V, meaning gate drive may be OK upstream, but the FET is not switching
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All voltages downstream from Q5240 are missing
🔧 Tentative Conclusion
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Q5240 appears to not be passing voltage, despite proper input and gate pull-up voltages
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Could be a failed MOSFET or gate drive logic not asserting properly
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Replacement part: FDMD8800, a DFN-14 dual N-channel MOSFET (30V, ~4 mΩ Rds(on), 13.3 × 4.93 mm package)
❓Open Questions
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Is it safe to conclude Q5240 is the failure point?
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Is there a known failure mode or upstream cause for failure in this power stage on M1 A2485 boards?
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Could gate signals be disabled by PMIC logic or missing enable pull-ups? (whatever that means)
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