A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

[KappaDev]

Hi all,

I have a A2251 board number 820-01949 which is in a 13" 2020 Macbook Pro and does not turn on.
Attempted DFU mode incase of corrupted T2, but never gets detected on second machine.
USB-C ampmeter shows drawing 13mA at 5.22V stable, never switches to 20V.

Checked and don't see any shorts on caps near CD3217 chips.
Schematics and boardview appear unavailable

Any ideas?

[mon2]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

1) How many USB ports on this logic board ?

2) Power down. Remove battery. For each USB port, check and post the resistance to ground for D+, D- lines.

3) Any liquid damage ?

4) The CD3215 / CD3217 are USB Power delivery devices that negotiate with the external power supply. They exchange power contracts and if all goes well, the 20V power rail will be selected. That is not the case for your logic board.

You can review the similar logic board operation on older models here:

https://www.logi.wiki/index.php/CD3215_Bootup_Sequence

It should be helpful.

Summary: Each and every CD3215/CD3217 must be operational to dial up the desired 20V to power this logic board.

Post your resistance values.

[piernov]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

820-00850 schematics/boardview can help.
PPBUS_G3H?

[KappaDev]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

1) How many USB ports on this logic board ?

2) Power down. Remove battery. For each USB port, check and post the resistance to ground for D+, D- lines.


3) Any liquid damage ?

4 USB-C ports on this board.

Battery removed, powered off. Apologize for ignorance, not sure where to measure D+ and D- from board side of USB-C.

No visible liquid damage under microscope, both sides of board clean.

820-00850 schematics/boardview can help.
PPBUS_G3H?

PPBUS_G3H appears missing, measured 0V at both sides of fuse (location similar to that on the 820-00850 board, hoping this is the same rail).
https://i.imgur.com/NuAaIAa.jpg
8 Ohms to ground, guess its shorted. Could this be caused by the CD3217?

[mon2]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

Use any passive (has no electronic parts onboard other than the connector) USB Type C breakout board.

Mate this USB Type C breakout board with the proper Type C to Type C cable (all wires should pass through from A / B side of the cable) - Arrow should have these at fair costs.

Then attach to your logic board. This is all so you can probe the signals on the Type C connector using the comfort of this breakout board.

As an example:

https://www.adafruit.com/product/4090

but there are many others out there / Amazon / Aliexpress.

This will allow you to review the status of the CD3215 / CD3217 which may have been nuked by the previous owner during the power delivery contract @ 20V but hitting one of the CCx lines. The new generation of type C ICs offer protection against this event but know from personal experience that I almost burnt my hands with USB PD 1.0 designs a few years ago. Reported the fault to VIA Semiconductor who agreed and revised their silicon.

TI has devices that protect against this transient event. During removal of a 20V rail the dainty pins slip and short across 5 volt only tolerant pins and often nuke the controller IC.

Again, this is just a FYI on what may have happened. If you see different resistance readings across the D+ / D- on the port(s) - the one that may appear to be "off the normal resistance" could be a culprit. If one CD321x device is non-working then this will halt the 20V negotiation.

[piernov]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

8 Ohms to ground, guess its shorted. Could this be caused by the CD3217?

No. Few ohms to ground typically means shorted high-side MOSFET to CPU.

[KappaDev]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

No. Few ohms to ground typically means shorted high-side MOSFET to CPU.

Understood. Safe to inject 1V under thermal camera inspection?

[KappaDev]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

No. Few ohms to ground typically means shorted high-side MOSFET to CPU.

In the event of shorted MOSFET to CPU, should I expect a coil to have similarly low resistance to GND? With battery unplugged and without DCIN, fuse goes to 0Ohms to GND. Haven't injected any voltage in-case MOSFET is to CPU don't want to kill it, but do have thermal camera if needed to take that route. Checked top side coil resistance in image below:
https://i.imgur.com/ymRyZbn.jpg

Despite picture, measurements taken without battery connected.

[NotAFish]

Re: A2251 820-01949 2020 Macbook Pro Stuck at 5V 13mA

Here you go in case you still need it.