A2338 820-02020 Stuck at 5V, meter resets

[ferrc95]

The board arrived very clean, with no traces of moisture or corrosion.

Initially, a part of one of the CD3217B12s was heating up, so I purchased a new CD3217B12, which wasn't specified in the purchase announcement as being compatible with the A2338. The short circuit disappeared, but it was still stuck at 5V. So I decided to buy another CD3217B12 specific to my model, but after replacing it, it remained the same.

PPBUS_AON is 12.3V. Before the reset, it drops to 12V, remains there for a few seconds, and then drops until it restarts.

The USB power meter shows a consumption of about 177 mAh, which gradually decreases to zero and then restarts, then restarts again.

[ferrc95]

Up

[mon2]

Do not have access to my schematics and am out of the office till next week- check if there is a fuse on PPBUS_AON. Flux and remove this fuse. Then power up again. Test if this power rail is still power cycling at the producer side (before the fuse).

[ferrc95]

Hi, thanks for responding. Yes, I did the fuse removal test a few days ago and the voltage remains constant at 12.3V without resetting.

[mon2]

Measure the resistance to ground of each inductor on the board. You are on the hunt for any power rail that may have a lower than normal resistance that will denote a shorted part on that rail. List all suspects. Downstream power rails are built by using this ppbus_aon rail as the high side of the next lower voltage rail. Each is a suspect.

[ferrc95]

Hi again, I attach the resistance measurements of all the inductors.

[ferrc95]

Up

I think the problem may be in the U8100, due to the 22 Ohm resistance of the L8120 inductor.

Pd: I just saw that I put Omhs instead of Ohms in the measurements file

[ferrc95]

Should I inject 1V and see if any point heats up?

[mon2]

Review this article on the PD controllers:

https://repair.wiki/w/Apple_ACE2_Controllers

[ferrc95]

But do you think it's due to the PD negotiation? If that were the case, shouldn't it stay at 5V without restarting in a loop?

[ferrc95]

Up

[mon2]

https://repair.wiki/w/MacBook_Pro_A2...p_meter_repair

[ferrc95]

Hi, thanks for the info. The difference I see is that in my case, I do have all the voltages. Even so, I've taken measurements of PP3v3_S2 and PP1v25_S2 and got these results:

PP3v3_S2 -> 0.402 (similar to the typical value of ~0.440)
PP1v25_S2 -> 0.275 (far from the typical value of ~0.490, do you think the problem might be here?)

I also injected 1V 1A into L8120 and got a current draw of 0.110A. Do you consider 22 ohms in the inductor to be normal?