Apple silicon Macs inherit from iphone/ipad platform. there are many similarities and repair techniques which could be adopted from the iPhone repair community.
Apple introduced M1 machines in the year 2020. Generally, the M1 platform has very few similarities with the classical PC Intel platform. However, since the T2 platform was somewhat of a bridge to Apple’s own platform, there are lots of well-known parts from T2 circuits moved to the new platform (like Display/Backlight, SSD, trackpad and keyboard operation, battery charging controller, and many other things).
1 - Putting an Apple Silicon Mac into DFU mode — key combination and method
The key combination to put an Apple silicon Mac into DFU mode — with reliable timing, the correct port, battery notes, and the restore logs for Revive and Restore.
DFU mode (Device Firmware Update) is the prerequisite for any Revive or Restore of an Apple silicon Mac. Unlike recovery mode, the device shows no image while in DFU — no Apple logo, no display, and on MagSafe no charging LED either. The screen stays fully black; that is normal and not a fault.
Since macOS Sonoma, Apple Configurator is no longer required
As of macOS Sonoma (14), a Mac in DFU mode can be revived or restored directly from the Finder on a second Mac — Apple Configurator 2 is no longer needed. The host detects the DFU-mode device and shows Revive Mac and Restore Mac buttons in Finder. Configurator still works, but is only needed for older host systems or batch workflows.
Requirements
A second Mac (host) running macOS Sonoma 14 or later for the Finder method (or Apple Configurator 2 on older systems).
A USB-C cable that supports data and charging (e.g. the Apple USB-C Charge Cable) — not a Thunderbolt 3 cable, and not a charge-only cable.
A connection to the correct DFU port on the target (see below).
The target must have some charge (see the battery note below).
The key combination and timing
On Apple silicon MacBooks you use three keys plus the power button (Touch ID):
Left Control (⌃)
Left Option (⌥)
Right Shift (⇧)
Power button (Touch ID, top right)
Sequence:
Shut the device down completely.
Press Power + left Control + left Option + right Shift at the same time and hold for exactly 10 seconds (count it out deliberately).
After exactly 10 seconds, release the three keys — but keep holding the power button.
Keep holding power for another ~5–10 seconds, until the large DFU window appears on the host.
Only then release the power button.
Precise timing is critical (Mr. Macintosh's method)
The reliable, counted 10-second method comes from Mac admin Mr. Macintosh and hits a near-100% success rate in practice. Apple’s own note only says a vague “about 10 seconds” — the real trick is counting precisely instead of estimating. If no DFU window appears within ~20 seconds total, stop and start over.
Only one specific port on the target is the DFU port. On the wrong port no DFU window appears, no matter how clean your timing is. The location depends on the model and changed on the 2025 models — Apple describes each position “facing the left side of the Mac,” i.e. among the USB-C ports on the left side of the device:
MacBook Air up to 2024 / most MacBook Pro: the front of the two left-side ports (Apple: “the leftmost USB-C port when facing the left side”).
MacBook Air 2025 and later, and the 14" base-M4/M5 MacBook Pro: the other of the two left-side ports (Apple: “the rightmost USB-C port when facing the left side”) — not the right side of the device, but the second left-side port.
If no DFU window appears after a clean 10-second attempt, the port is usually just wrong — use the other port on the device and try again. It must be a USB-C data-and-charge cable, not a charge-only cable and not a Thunderbolt 3 cable.
The battery must be charged — and the “pre-SMC” trick
A Revive or Restore won’t work on a completely empty battery — the device needs some charge. It gets tricky when a device is stuck in the pre-SMC state: it won’t charge from the cable at all and looks “dead.”
The way out: start a Revive anyway. Even if the Revive fails on a timeout, the device loads a RAMDisk with a working SMC component during the attempt, which lets the Mac charge again. Then leave it on the cable, let it charge a bit, and try the Revive again — now with enough charge.
Detailed logs in Console (Console.app)
When the Revive/Restore is run from the Finder, macOS writes a very detailed log on the host. The whole process can be followed live and reviewed afterwards in Console (Console.app).
These logs are invaluable for proper diagnosis: they show exactly which phase a job fails in — firmware write, the transition step, or a USB problem — and give the specific error code (e.g. the 4042 error in the transition step). Without these logs a restore is guesswork; with them you can decide deliberately whether a Revive, a different IPSW, or a hardware fix is needed.
Technical DFU without a working keyboard (jumper method)
If the device can’t be put into DFU from the keyboard — a dead keyboard, a disconnected top case, or a bare logic board on the bench — the FORCE_DFU signal can be triggered on the board directly. The signal is pulled to the correct rail (PP1V25 / 1.25 V); on most boards the pull-up resistor is not populated, so you have to work from the schematic. This method works with no keyboard at all and is far more reliable in day-to-day repair.
repair.wiki — community documentation on device repair
2 - MacBook suddenly stopped working after the update to macOS 26.4.1
Your MacBook won’t boot after the 26.4.1 update. Why a restore fails with error 4042 and how to recover the machine without losing data.
Symptoms / Affected machines
John Ternus experiencing firmware failure after transporting his Mac in a backpack — no picture and full fan speed.
No matter how exactly update was installed, boot failure happens either right after the update or some time later.
from power perspective - 20V 0.1-0.3A, full system power with slightly warm CPU. No screen, no chime, trackpad haptic or keyboard activity.
Affected machines so far:
MacBook Pro from M2 to M4, but probably might happen to MacBook Air too.
What’s actually happening
The failure is in the boot chain — the iLLB → iBoot → kernel transition. According to the speculation investigation so far, the device stops at iBoot in a non-recoverable panic state. no further evidence has been found in the logs yet, and this will be updated as more time with an affected machine allows. The device does not necessarily fail immediately: sometimes the failure only appears on a full restart — which can happen weeks after the faulty update was installed, for example once the battery has gone completely empty. So a device may still boot normally right after the update is installed and only fail weeks later, or whenever the next full reboot occurs.
The log — error code 4042
A typical excerpt from the log in Console (Console.app):
[17:59:01.7501] Finished DFU Restore Phase: Successful
[17:59:01.7505] Changing state from 'Restoring' to 'Transitioning'
[17:59:01.7505] Creating timer to monitor transition
[17:59:01.7505] Creating a timer for 10 minutes
[17:59:01.8554] DFU mode device disconnected
[17:59:01.8554] Device disconnected during transition
[18:09:01.7592] Timer fired to timeout transitioning device
[18:09:01.7596] Changing state from 'Transitioning' to 'Disappeared'
[18:09:01.7596] Device disappeared during transition
[18:09:01.7597] Device isn't booted but USB is up.
[18:09:01.7655] Restore completed, status: 4042
[18:09:01.7655] Elapsed time (in seconds): 607
[18:09:01.7655] Failure Description:
[18:09:01.7655] Depth:0 Code:4042 Error:Gave up waiting for device to transition from DFU state to DFU state.
[18:09:01.7664] AMPDevicesAgent: Restore error 4042
In plain language: LLB payload upload was successful. The device then disconnected and never came back into update mode within the 10-minute window. The process gave up and reported 4042.
The safe fix
Important warning up front: do not attempt a full Restore. Restore erases all user data and hits the same 4042 because the target firmware is the broken 26.4.1.
The double revive is no longer needed since macOS 26.5
Since the 26.5 update, the double revive is normally no longer required. macOS 26.5 corrects the iLLB (low-level bootloader); the stuck boot was most likely in the iLLB → iBoot transition (or onward to the kernel). The faulty 26.4.1 update could not fix itself — it stayed stuck for the same reason the failure happened in the first place.
The simpler path: do a single Revive until the device boots again — then back up the data — and only then run the OS update normally.
Revive and Restore are done from the Finder on a second Mac since macOS Sonoma (see DFU mode on Apple Silicon).
Double Revive — fallback technique
Since macOS 26.5 this path is normally no longer needed. It stays documented as a technique because it can help in similar cases which might happen:
Revive (not Restore!) using an earlier IPSW — one version back, e.g. 26.4.0 or the latest 26.3.x. Revive reinstalls firmware and recoveryOS only; user APFS volumes are untouched.
The device now boots normally on the earlier firmware. Wait for the login screen.
Revive again — this time with the current IPSW.
Data preserved; machine is on current firmware.
Choosing a specific IPSW
To pick an IPSW other than the latest, hold the Option key while clicking Revive (or Restore) and select the file. The IPSW’s release date must not be earlier than your Mac’s release date — an older image simply won’t work and fails with a compatibility error.
What NOT to do
Do not Restore — data loss and the same 4042 error.
Do not have the logic board repaired or replaced. There are numerous reports that even several Apple Authorized Service Providers wrote this off as a “hardware” defect. €800 for a new board plus data loss is, in the vast majority of cases, completely unnecessary.
If you’re not sure — find the right repair shop
If you’re not sure, look for a repair shop that knows this issue. The usual quote for such a repair should be roughly the same as what people charge for a system installation on a Windows or Mac machine — technically it is almost the same thing.
repair.wiki — community documentation on device repair
3 - Signal-line analysis for diagnosing bootloops on Apple Silicon devices
Using a logic analyzer on the management buses (I²C, SPMI)
Scope
On Apple-Silicon-class devices, signal-line analysis — probing the device’s internal
management buses with a logic analyzer — is a way to gather diagnostic information
before resorting to an SoC swap. CPU swap is often overestimated despite being generally a dangerous procedure. Even if done on controlled BGA Soldering station, CPU and NAND will get thermal shock which might harm and even destroy them - you will never know.
I will try to describe some methods and ideas about such diagnostics.
iPhone iOS / iPadOS is a diagnostic nightmare if no panic log available.
The iPad Pro 2020 uses the A12Z, a CPU quite similar to the M1 — the Apple
DTK (Developer Transition Kit) even ran macOS on the same A12Z silicon.
Despite that hardware closeness, iPadOS is a very closed box, with close to zero
possibility to troubleshoot bootloops. Recovery and DFU are firmware/restore states, not a usable OS — there is no terminal and no way to mount or read the user data partition, unlike macOS Recovery. The user data is also cryptographically out of reach: on A12-class SoCs (the A12Z included) the Secure Enclave Boot ROM locks the passcode seed bit the moment the device enters DFU or Recovery, so Data Protection class A/B/C data stays encrypted in those modes, and the file-system key hierarchy is rooted in the SEP’s fused UID key, which never leaves the AES engine (src: Apple Platform Security). This leaves a very limited
set of diagnostic possibilities. If you don’t have panic log which requires you to have mostly functional device, if device goes through soft-update well - you are almost blind, at least it seems bareboard soft-updates quite well, in many cases - iPhone will go through that being halved from its modem board. This is actually a big difference to macOS - macOS would boot with half board dead (sensors, peripherals, controllers) but won’t go through software update and fail with useful log entry. Unlike Macs you can’t even try old IPSW — every restore needs a fresh Apple-signed ticket tied to the device ECID, and Apple stops signing old versions, so downgrades fail outside the signing window (or without saved SHSH2 blobs).
Worth noting: on checkm8 / bootrom-exploitable devices (up to A11 - iPhone X and earlier) this is a completely different story. There checkm8 lets you ramdisk-boot and even dump SEP memory, so partial filesystem / BFU (before first unlock) extraction is on the table and you can actually do real diagnostics - the box is barely closed. A12 patched that bootrom hole for good, so on the A12Z (and anything newer) none of it works anymore. That’s exactly why this iPad is such a pain - it sits right on the wrong side of that line. User data is secure from being restored.
It is therefore understandable that standard iPhone/iPad “data recovery” often ends up with
no diagnostic at all and simply a swap. However, a CPU swap carries a certain risk of
further damage even when done properly. General rule of thumb: avoid heating SOC + NAND more than 200C unless completely necessary. Always cover such parts, put heatsinks.
The case
An iPad Pro 12.9″ (2020) that caught a bootloop close to the end of boot.
Sidenote: Usually iPads and iPhones are out of my scope, but customer was referred to me and my knowledge (unfortunately) on scam “standards” of many data recovery companies convinced me to give it a shot.
TLDR - I recommended customer to wait till major software update after I fixed DFU mode. That was sort of “gut feeling” but also I did not know symptoms how it went off.
After few weeks of struggle/analyze, finding a clue in GPU failure, then replacing PMIC, I contacted one very reputable and kind repair colleague with broader expertise (link below) in Apple mobiles, and told me that IS, in fact, most likely a SOFTWARE problem and “swap” won’t do anything good to this device, we should wait. Full circle. Hope it works :) .
How it died
The device was low on battery, and the GPU supposedly crashed: a grayed-out
UI with a loading circle, which indicates the system waiting on a response from the
hardware GPU driver — supposedly blinked few times and went off.
The bootloop clearly happens exactly on the display-resolution change that shortly
precedes the crash. iPads SoC clearly has two video modes, similar to the Intel iGPU
platform: the GPU is only powered and utilized when there is GPU load (only short power check during SiliconInit EFI POST). I guess GPU is always needed to render the fancy-wobbly translucent Liquid Glass UI of iPadOS 26, but it is not used in the recovery state.
The built-in recovery state — a low-load screen where the GPU is not utilized. Trying to “recover” immediately “fails” which might actually indicate a software issue. Soft-update ends up with “swipe up to recover data, then falls back to the same bootloop.
Findings in this unit
Two distinct issues were found:
A damaged CD3217B12 IC: shorted middle D+/D- pair — most likely from ESD, and totally unrelated to the
actual boot problem. With it damaged, the device was not visible or recognizable
over USB in DFU mode. This chip unfortunately has OTP (configures BUS_POWER behaviour), so you need to source it (preferably with rom) from the same platform (in my case, iPad Air was compatible enough).
Thanks to David Lecomte and his strap i2c config/BUS_POWER fix method, briefly: (https://logi.wiki/index.php/CD3217_and_T2_Power_on_Sequence), fully:(https://repair.wiki/w/Apple_ACE2_Controllers) Mac OTP was solved, but iPads have clearly a different firmware behaviour (for example, 15V is only negotiated quite deep into iPadOS boot, which is very different). CD3217 also does not have a “dumb” no-smc mode. Also “clean unused” CD3217 with blank OTP tend to work until battery is completely depleted once. It looks like BUS_POWER should be also physically strapped to usb-powered LDO for it to properly work but decided shortcut and replace it from donor.
An absent VDD_GPU during the whole boot phase, together with a clear
overheating “rainbow” on the VDD_GPU edge of the main PMIC. Turned out to be a useless move, but I replaced the PMIC. I seen such PMIC failed on MacBooks, so why not.
The main PMIC (343S00832). The oily stain around the chip came from the degraded thermal pad (a bit mixed with IPA), but a clear “rainbow”-like pattern + delaminated corner at pin1 is clearly visible
Boardview/schematic (820-01798): the GPU power rail PPVDD_GPU at the SoC (U8100) — inductor L8112 → GPU VDD, L8480 → GPU SRAM. Both DrMOS drivers are placed on “rainbow” edge of the chip.
Bus diagnostics
This is where signal-line analysis might (not?) help. The possible paths are I²C and
the SPMI diagnostic. The SPMI work is based on available sources —
SPMI kext decompilation and a bit documentation available from IC manufacturer.
Logic analyzer tapped onto the bus lines of the opened iPad. To get to some pads I had to cut metal cover around Logicboard with sidecutters. Since this is data recovery case, optics does not matter and it is the most safe method to get access to both CD3217 ROM and SPMI bridge points. I’m not a fan of drilling shield away since metal dust is a bad spice on such tiny board.
I²C
The I²C lines were also checked to rule out a bad audio codec and similar. iPad played the charging
chime, but it was a bit shorter than normal. I first removed the shields to clearly see if one amp could spike warmspot during chime, but unfortunately they were all completely fine. Bad Amp can cause random shutdown or glitch on power supplies. To be 100% sure, I checked if all Amps are responding ACK during init / chime.
(Here is a video explaining the method on MacBooks, but that’s effectively almost identical circuit and Speakeramp on iPad.)
SPMI (work in progress)
SPMI (System Power Management Interface) is a two-wire serial bus defined by the
MIPI Alliance for communication between a system processor and power-management ICs
(PMICs). — MIPI Alliance, SPMI specification
This matters going forward: new Macs, iPads and iPhones use SPMI mostly as the internal
management interface. For example, our not so beloved SN25 communicates solely on SPMI.
A logic-analyzer dump still makes it possible to recognize which device failed to
respond or returned an error code. Unlike I²C, there is currently no public
information on what addresses the devices use, also not listed in schematics — but the mapping could be discovered the
old-school way, by artificially blocking devices one by one during analysis. But unfortunately this won’t help to split power domains on PMICs.
What I found:
Master (SoC SMC element) communicates to 3 slave devices, also there is authentication step.
Auth step is basically a very very thin ice - we are already zero steps away from finding that PMIC chips became tied to concrete board (this will effectively end half of repairs/swap method). It already seems to be the case with SN25* on most recent MacBooks (rom+sn25 pairing) but it requires better community-based investigation.
SIDs found in traffic are not just devices but functional domains. I believe each power block (CPU, GPU, Auxiliary etc) represents a separate domain/SID. This makes SID identification way harder, maybe partially doable with perfectly synced thermal camera or logic analyzer connected to power outputs.
Good level of decoding will potentially allow to catch power issues and even current sense/voltage values from each power rail.
Currently i am working on simple streaming adapter to scan SPMI directly.
Hardware repair becomes weird “firmware hacking” with no light ahead
The efficiency of this method may be marginal on Apple mobile devices. But since SPMI became more or less main way of communicating, decoding might become a replacement of enable signals (effectively SPMI completely substitutes such signals). This tendency could also be observed in Intel PC Laptop domain: instead of normal s0-s5 signals some laptops already implement “virtual wire” signals over eSPI. (see Intel’s documentation: the eSPI Interface Base Specification and the PCH datasheet’s eSPI section, where sleep/power-state signals such as SLP_S3#/S4#/S5# are carried as eSPI “virtual wires” instead of dedicated pins), S* becomes just a GPIO-driven indicator/testpoint.
Special thanks
Special thanks to Rico Cerva - a true and honest professional. Unfortunately, when i started to dig into the iPad/iPhone data recovery scene, i found scammers and “swap-monkeys” to absolutely dominate the market.
Meeting such people restores my belief in our trade.
