A2338 820-02020 5v 0.04A PP3V8_AON low

[Gueric]

Hey mon, its me again (sorry) so after fixing my own Mac I’m back to try and fix another one.

I changed a CD3217 on this one. And it started bootlooping a few hours after the fix.

5v, 0.20-0.30A for the first few seconds then drops to 0.00-0.05A.

PPBUS_AON is 12v.
PP5V_S2 is present.
PP1V25_S2 is present.
PP3V3_S2 is present.
PP3V8_AON is 3.8v, but its diode mode was abnormally low (.150v instead .350v)
And to make it even worse I accidentally touched PPBUS and 3V8 with my meter and the resistance is now 100 ohms (don’t remember how much it was before touching the 2 lines)
3V8 is still present when plugging the USB though, and when it happened the board was pulling 0.03A, and the ampmeter behaviour hasn’t changed.

I checked all CD3217s LDOs, all present.
I don’t think they’re the issue here.

something else I noticed on this board, a knocked off PPDCIN_AON_CHGR_R cap. I don’t think it’d prevent the board from working.

Should I just try and inject 1-2V into PP3V8_AON ?
theres RD610 I could remove to isolate all the PMU side 3V8.

thank you very much, again

[mon2]

What is the exact voltage to ground of PPBUS_AON?

PP3V8_AON is ok if you see 3v8.

[Gueric]

mon2 PPBUS_AON is a stable 12.01v.
i remember i tried to replace a second time the CD3217 just in case and nothing changed.

i agree with you on PP3V8_AON, but is it fine even if lts 100 ohm as i said? It is 3.8v as expected so i guess its fine as you said

[Gueric]

also, I checked SOC_DFU_STATUS and it's around 1v. does that mean it's in DFU mode and that would explain the 5V instead of 20? I don't know much about it

[mon2]

https://boards.rossmanngroup.com/thr...fu-mode.63954/

If machine is in DFU mode, then SOC_DFU_STATUS wil be high.
0V means the machine is in normal state, not DFU.

To me, this logic level is too low but can you confirm if there is a status LED @ DSW050 on your board? This LED will enable if you are in the DFU mode.

The logic level will enable the mosfet and the mosfet will sink the current required to enable the LED to be visible.

[Gueric]

Hey mon2.

For some crazy reason im having the exact same issue i had with my own macbook a few days ago. I decided to put the board back together, boot it up, and it instantly negotiated 20v. It booted fine, no more bootlooping. But the behaviour is inconsistent now. Sometimes 20v at 0.00A, sometimes 5v at 0.42A, and sometimes normal behaviour = 20v and a few amps, charging battery.

im currently reinstalling macOS to see if it might solve the issue.

[mon2]

Are you using the same power adapter? Same power cable as the other unit? Be sure the contacts are clean. We always keep fresh 100W rated USB-C cables to rule out the interfaces.

[Gueric]

mon2 I’m using the same power adapter always, but it’s a cheap 100W unit. It hurts to pay this much but I should buy a proper Apple unit.


back to the laptop. I did a full wipe, and it worked, charged every single time. Disconnected the battery, put every screw back on, plugged the battery back in, started to go crazy again. Would bootloop every time I tried to enter the password.

i then tried to DFU it, I managed to enter DFU and start the process but it kept rebooting and tried to boot into the OS while the process was underway.

The DFU obviously failed, and the laptop ended up booting on its own fine. Now it’s working and I’m scared to shut it down 😂

I think the software is somehow completely corrupt somewhere, I don’t think it’s hardware anymore

mon2

[Gueric]

Okay so. mon2 it is still bootlooping for no reason at random moments. It installed macOS Sequoia fine etc, then started bootlooping on the Apple logo again. For some odd reasons, starting into the recoveryOS doesn’t make the laptop bootloop. I can even navigate the startup options like disk info etc…
Do you have any idea what might be
happening ?

[mon2]

We have a few units like yours in the building at the office for my never ending work pile. Are the results better if out of the case? If yes, review it step by step. I recall one incident (a bit on topic) where the unit worked out of the case but not when put back together. After the 2nd or 3rd round of this assembly / disassembly, found that the audio board for that macbook (rather recent) was to blame. No schematics for the audio board but for sure had a shorted cap onboard. There were only 3-5 of them so played, 'find waldo' and on the 2nd cap removal, unit was fixed. The client then came clean and said we were the 3rd shop he brought the unit to AFTER Apple said to toss it and buy another. The audio board is $120 USD on Aliexpress.

Unplug everything that is possible to see if you can halt this bootlooping fault. It does not help if you have thermal issues that cannot be spotted. Personally searching for a more portable thermal camera for my phone to get into the awkward angles on the board. Perhaps at the next electronics fair in HK. They always bring in the latest widgets for repair, etc. at the mobile fair.

[Gueric]

I might try to do this. Unplugging audio board, maybe speakers etc… but in my case it does not bootloop while reinstalling macOS and while browsing the recovery options. Has this specific case ever happened to you? Right now I’ve erased the whole disk, reinstalled the OS, and created a random account.

im pretty sure its gonna bootloop again tonight but its tricky to know why.

I’m wondering if this 100 ohm PP3V8_AON has anything to do with that. Anyway, thanks mon2

[mon2]

Try the internet recovery boot mode. We do this often to rule out the onboard SSD media / OS, etc. Then you are running out of RAM only. Worth a try.

[Gueric]

Hey mon2 this might help you with your pile of MacBooks so I thought I’d share.
I’m still trying to figure out why this M1 shuts down randomly after a few minutes/hours.

im currently doing a test, which consists in playing a 10 hour video non stop WITH THE POWER ADAPTER PLUGGED IN.

its been almost 24 hours now, zero bootlooping or unexpected shutdowns so far.

i might do the same but on battery power to rule out a defective battery (even though macOS tells me its in normal condition)

I reckon that would explain the random shutdowns and macOS corruption.