| MacBook Pro A2251 Not turning on, 0.00-0.05A current draw at 5V repair | |
|---|---|
| Device | |
| Affects part(s) | |
| Needs equipment | |
| Difficulty | |
| Type | |
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Problem description
Diagnosing and resolving issues where a MacBook (820-01949) remains stuck on 5V with low current draw (~0.00–0.02 A) as indicated by a USB-C current meter. Commonly, this is attributed to a short to ground on the PPBUS_G3H power rail. Differentiate this from cases where one port reads 5V ~0.12–0.25 A while another reads 5V ≈5V 0.02 A (CD3217 issue), and where all ports show 5V ~0.00–0.02 A (PPBUS_G3H issue or T2 corruption).
Symptoms
- MacBook not turning on and is stuck on 5V with low current draw (~0.00–0.02 A) as measured by USB-C amp meter.
- Absent PPBUS_G3H voltage due to a short or creation problem.
- Device stuck in DFU mode due to corrupt T2/BridgeOs firmware.
- Absent or shorted PP3v3_G3H_RTC voltage.
- Failed CD3217 USB C controller (U3100_T, U3100_X, U3100_W, U3100_R)
- Short to ground on any of the power rails generated by U7800 that power the T2 chip, such as PP1v8_SLPS2R or PP1v1_SLPS2R.
- Missing U7800 input power
- Missing or shorted SLPS2R line. (Most commonly PP1v8_SLPS2R due to a short to ground.
- Non-specific areas of corrosion causing T2 or CD3217 communication issues.
Solution
Diagnostic Steps
Check for DFU or Recovery Mode
- Connect the MacBook to another Mac via the master port and use Apple Configurator 2 to verify if it's in DFU mode.
- If in DFU mode, proceed to "Device stuck in DFU mode due to corrupt T2 firmware" repair steps.
Check PPBUS_G3H Voltage
- Measure voltage on PPBUS_G3H (C6584 or similar) using a multimeter.
- Compare measured voltages to reference ranges.
- Interpret results based on voltage values and proceed to appropriate repair steps.
Check PP3v3_G3H_RTC Voltage
- Measure PP3v3_G3H_RTC on a capacitor or resistor near CD3217 (C3100_W recommended).
- Compare measured values to normal range (~3.3V).
- Proceed based on measurement results.
Check PP3v3_G3H_PMU_VDDMAIN Voltage
- Measure PP3v3_G3H_PMU_VDDMAIN on a capacitor near U7800 (C78B0 recommended).
- Compare measured values to normal range (~3.3V).
- Interpret results and proceed as necessary.
Repair Steps
Device Stuck in DFU Mode Due to Corrupt T2 Firmware
- Revive T2 firmware using Apple Configurator 2 on another Mac.
- Follow steps to restore firmware, ensuring macOS is updated.
PPBUS_G3H Short to Ground
- Inject ~1V with 5A limit into PPBUS_G3H using DC power supply.
- Localize shorted component using thermal imaging or isopropyl alcohol method.
- Replace the identified shorted component.
PPBUS_G3H Absent or Low with No Short
- Check if PPDCIN_G3H is reaching ISL9240 (U7000).
- If not, proceed to "CD3217 troubleshooting" if no short is found.
CD3217 Troubleshooting
- Check current sensing resistors: R7021, R7022, R7061, R7062.
- Replace ISL9240 and associated resistor if needed.
PP3v3_G3H_RTC Low or Absent
- Diagnose possible shorted capacitor around CD3217 or from CD3217 itself.
- Check GHGR_EN_MVR signal produced by ISL9240 (U7000).
- Replace ISL9240 (U7000) if enable signal is missing.
PP3v3_G3H_PMU_VDDMAIN Low or Absent
- Check R7900 resistor: ensure power to pin 1 and measure voltage on pin 2.
- Replace R7900 and retest if resistance is out of spec.
- If needed, investigate R6934/35 resistors for blowing.