820-02757 A2918 No Power Repair – UF400 and UF500 CD3217B13 Replaced

Fault Description

This 14-inch MacBook Pro A2918 with logic board 820-02757 came in with water damage and no power.

Initial USB-C meter readings were different between the two ports:

USB-C port 1: 5V / 0.0A stable
USB-C port 2: 5V / 0.3A stable

The board did not negotiate 20V and had no normal startup behaviour.

Initial Symptom

The first important clue was that the two USB-C ports did not behave the same.

One port showed:

5V / 0.0A stable

The other port showed:

5V / 0.3A stable

A port sitting at 5V / 0.0A usually means the charger is detected at a very basic level, but the USB-C controller on that side is not waking or communicating correctly. The board is not pulling meaningful current and cannot move forward in the power sequence.

The other port at 5V / 0.3A showed more activity, but still no 20V negotiation. So the board had more than a simple single-port charging issue.

Measurements Table

Test Point / Observation	Reading	Result
USB-C port 1	5V / 0.0A stable	Not OK
USB-C port 2	5V / 0.3A stable	Partial activity
PPBUS_G3H	0V	Not OK
FF200 pin 1 / PPDCIN_USBC_AON	0V	Not OK
After replacing UF400	Both ports 5V / 0.3A	First fault improved
CF508 pin 1 / PP3V3_UPC1_LDO	0V	Not OK
Final repair	UF500 replaced	Fixed
Final result	MacBook working	OK

Why UF400 Was Replaced First

The diagnosis started with the missing main input path.

Because PPBUS_G3H = 0V, the board had no main always-on power rail. Before checking later power rails, the first question was whether USB-C input power was entering the board correctly.

The measurement at FF200 pin 1 / PPDCIN_USBC_AON was:

PPDCIN_USBC_AON = 0V

That means the board was not receiving the expected USB-C input power on the AON input path.

With one port showing 5V / 0.0A and PPDCIN_USBC_AON missing, the most logical suspect was the USB-C/PD controller or input control path for that side. In this case, UF400 was replaced first.

After replacing UF400, the behaviour changed:

Both USB-C ports = 5V / 0.3A

That confirmed UF400 had been part of the fault. The first dead-looking port was now showing activity, but the MacBook still did not fully start, so diagnosis continued.

Why UF500 Was Replaced Next

After UF400 was replaced, both ports now showed 5V / 0.3A, but the board still did not complete normal power-up.

The next clue was:

CF508 pin 1 / PP3V3_UPC1_LDO = 0V

This rail is a local 3.3V LDO rail for the USB-C controller area. If this LDO rail is missing, the controller cannot operate correctly, even if the charger is connected and the port shows some current draw.

Because PP3V3_UPC1_LDO was 0V, the next logical suspect was the second USB-C controller area. Replacing UF500 restored the missing controller support rail and the MacBook powered on.

Circuit Logic

The fault was not solved by checking only one USB-C port. The board had a staged failure:

Stage 1:
Port 1 = 5V / 0.0A
PPDCIN_USBC_AON = 0V
PPBUS_G3H = 0V
→ UF400 suspected and replaced

After UF400 replacement:

Stage 2:
Both ports = 5V / 0.3A
Still no full startup
PP3V3_UPC1_LDO = 0V
→ UF500 suspected and replaced

The important reasoning is that USB-C current behaviour changed after UF400, proving the first repair moved the board forward. But because the second USB-C controller support rail was still missing, the board could not complete the next stage.

Final logic:

UF400 restored the dead input-side behaviour.
UF500 restored the missing USB-C controller LDO rail.
Both faults had to be repaired before the MacBook could work.

Repair Timeline

Step	Result
Customer reported water damage and no power	Confirmed
USB-C port 1 tested	5V / 0.0A stable
USB-C port 2 tested	5V / 0.3A stable
Checked PPBUS_G3H	0V
Checked FF200 pin 1	PPDCIN_USBC_AON = 0V
First fault direction	UF400 / USB-C input path
Replaced UF400	Both ports changed to 5V / 0.3A
Checked CF508 pin 1	PP3V3_UPC1_LDO = 0V
Second fault direction	UF500 / USB-C controller LDO fault
Replaced UF500	MacBook powered on
Final test	MacBook working

Key Lesson

When a MacBook has water damage and no power, the USB-C meter reading can show which part of the power path is alive.

In this case:

5V / 0.0A on one port
PPDCIN_USBC_AON = 0V
PPBUS_G3H = 0V

pointed to the first USB-C controller/input-side fault, so UF400 was replaced.

After that, both ports improved to:

5V / 0.3A

but the board still did not start. The next missing clue was:

PP3V3_UPC1_LDO = 0V

That pointed to the second controller-side fault, so UF500 was replaced.

The key lesson is that water damage can create multiple partial faults in the USB-C power path. One replaced chip may move the board forward, but the repair is not complete until the next missing rail is found.

Final Fix

The final repair was:

confirmed water damage and no power;
tested both USB-C ports;
found one port at 5V / 0.0A and one at 5V / 0.3A;
confirmed PPBUS_G3H was 0V;
confirmed PPDCIN_USBC_AON was missing at FF200 pin 1;
replaced UF400;
both ports improved to 5V / 0.3A;
confirmed PP3V3_UPC1_LDO was missing at CF508 pin 1;
replaced UF500;
MacBook powered on and worked normally.

Case Summary

Item	Details
Device	MacBook Pro 14-inch
Model	A2918
Logic board	820-02757
Customer fault	Water damage, no power
Initial USB-C port 1	5V / 0.0A stable
Initial USB-C port 2	5V / 0.3A stable
PPBUS_G3H	0V
FF200 pin 1 / PPDCIN_USBC_AON	0V
First faulty area	UF400
After replacing UF400	Both ports 5V / 0.3A
CF508 pin 1 / PP3V3_UPC1_LDO	0V
Second faulty area	UF500
Repair	Replaced UF400 and UF500
Final result	MacBook working

This technical note is part of our Mac logic board repair case study collection, where we document real component-level faults, measurements and repair outcomes. View more here:
Mac Logic Board Repair Case Studies

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