MacBook Pro A1707 no power 20v

[federicoc]

Hi everyone,

I have a MacBook Pro A1707 logic board that does not power on. Below are the measurements taken.

Measured with a USB-C power meter on the ports:
• 20V present
• Current draw: 0A most of the time
• Occasionally spikes to ~0.500A, then drops back to 0A

Main rails (stable)
• PPBUS_G3H: 12.6V
• PP3V3_G3H: 3.3V
• PP3V0_G3H: 3V
• PP5V_PMICLDO: 5V

Signals
• SMC_RESET_L: 3.3V
• RTC_RESET_L: 3V
• PCH_SRTCRST_L: 3V
• PCH_INTRUDER_L: 2.8V
• PM_SLP_S5_L: 0V
• PM_SLP_SUS_L: 3.3V but oscillates

Unstable rails (oscillating)
• PP5V_S5: oscillates
• PP3V3_S5: oscillates
• PP3V3_SUS: oscillates
• PP1V8_SUS: oscillates

Additionally, L8030 output is oscillating.

Has anyone encountered a similar issue on this model?

Thanks.

[mon2]

Working on a similar pig in the shop now (A1706) and not having fun. At least 2 of the CD3215 are defective, possibly more due to fake(?) power adapters being used. Client wants it working to retrieve their data.

Test the voltage to ground of:

SMBUS_SMC_5_G3H_SCL
SMBUS_SMC_5_G3H_SDA

Should be ~3v42. If it is not, test the resistance to ground for each of these signals. These signals are open-drain signals that must not be shunted to allow for the PPBUS_G3H to be escalated to ~13v for the normal boot process.

[federicoc]

Voltage:
SMBUS_SMC_5_G3H_SCL 3.0-3.4
SMBUS_SMC_5_G3H_SDA 3.0-3.4
the value is not stable, it reaches 3.4 then drops to around 3 and then goes back up

resistance to ground
SMBUS_SMC_5_G3H_SCL 0.412
SMBUS_SMC_5_G3H_SDA 0.412

[mon2]

The lines are not shorted / shunted so not the fault.

My bad - your board is at the proper PPBUS_G3H voltage of 12v6 for a normal boot. Too many numbers in my head.

Suspecting that you have a shorted part on the board that is causing this power cycling. Test the resistance to ground of each and every inductor (grey coils). Report any low resistance to ground for a review.

[federicoc]

L8410 ppvin_s0sw_lcdbklt 0.840

L7660 pp3v3_s5 0.360

L7660 pp5v_s4 0.420

L7900 pp1v2_phase 0.079

L7960 ppvccio_s0_cpu 0.027

L8000 p1vs4_phase 0.080

L7030 tba_phase 0.330

Lb700 p5vusbct 0.168

La300 gpufb_ll 0.049

L3500 p5vusbcx 0.177

Anything else you suggest I measure?
How do they look?
Thanks for your help

[mon2]

Brother, I think we are almost in parallel on the A1706 case.

Your USB rails are also looking low.

Lb700 p5vusbct 0.168
L3500 p5vusbcx 0.177

What is the voltage that you measure for these inductors to ground?

Concerned about the following:

A diode mode measurement of 0.080V on L8000 (P1VS4_PHASE) is not normal and typically indicates a short circuit or a severely degraded component on that rail.

Measurement Analysis

• Expected Reading: For a 1.4V phase rail like P1VS4_PHASE on a MacBook Pro (such as the A1707), a healthy diode mode reading is typically between 0.300V and 0.450V.
• The 0.080V Reading: This is a "low-ohm" state. While not a "dead short" (0.000V), it is low enough to prevent the power management IC (PMIC) from properly starting the rail.
• Common Causes:
  • A shorted decoupling capacitor on the PP1V4_S4 line.
  • A failed U8000 (the buck converter/controller for this rail).
  • Internal damage to the CPU/PCH if this rail feeds a core voltage or sensitive logic area.

Recommended Next Steps

• Resistance Check: Switch your multimeter to Ohms (Ω).
  • If the resistance is below 10–20Ω, you have a definitive short.
  • CPU/GPU rails often have naturally low resistance, but P1VS4 is a general logic rail and should be higher.
• Isolate the Rail: Remove L8000 and measure both pads.
  • This identifies if the short is on the "Source" side (U8000) or the "Load" side (the rest of the board).
• Voltage Injection: If you have a DC power supply, inject 1V (do not exceed 1.4V) onto the rail and use thermal imaging or isopropyl alcohol to find the component getting hot.

[federicoc]

I desalted 8000
These are the values: P1VS4_PHASE 0.400
PP1V_PCH_REG_R 0.040

Don't they seem normal to you?

[mon2]

These are diode mode measurements.

PP1V_PCH_REG_R 0.040

Looks low. Switch to the lowest resistance mode. Measure the resistance to ground of the same location. What is the resistance in ohms?

[federicoc]

89.4 ohms
I don't have a comparison board