MacBook Pro M3 Max
A2991 · X2681
Board Specifications
| Parameter | Value |
|---|---|
| Model Identifier | MacBook Pro 16" (A2991) – Mac15,7 / Mac15,9 |
| Board Number | X2681 MLB-S APPD |
| SoC | Apple M3 Max (H15S) – TSMC 3nm – 12-core CPU / 30-core GPU / 16-core Neural Engine |
| Unified Memory | 36GB / 48GB / 64GB / 128GB LPDDR5 (soldered) |
| Storage | 512GB – 8TB NVMe (soldered, 2× or 4× NAND modules) |
| PMU | Apple Chapel H15 (T585_REF_PMU_CHAPEL_H15_0.42.0) |
| Charger IC | Mandola MP (T585_REF_CHARGER_MANDOLA_MP_0.0.12) |
| USB-C Controller | ACE3 (×3 ports) – T585_REF_USBC_LFKA_3PRT_ACE3_0.45.0 |
| MagSafe Controller | ACE3 – T585_REF_MAGSAFE_ACE3_0.4.3 |
| Schematic Revision | ECN 0045286995 – Engineering Released 2023-06-27 |
| BoardView Available | Yes – macbook-pro-m3-max-a2991_schematic_1.brd |
Parts Pairing Alert: Touch ID sensor and lid angle sensor are serialized to the logic board. Display swap between machines causes artifacting unless calibrated via Apple's Repair Assistant. Battery requires calibration after replacement.
Voltage Rails Reference
| Rail Name | Nominal | State | Regulator / Source | Schematic Page | Notes |
|---|---|---|---|---|---|
| PPBUS_G3H | 8.0–20V | G3H | Battery / USB-C PD / MagSafe | 27, 52 | Main power bus – always present with power source. If absent: check battery connector flex, MagSafe controller U5500, charger IC input. |
| PP3V8_AON | 3.8V | AON | ICEMAN HP VR – U3200 | 57 | Always-On domain for PMU/SMC wake. If absent: check U3200 enable, inductor L3200. |
| PP3V3_G3H | 3.3V | G3H | Chapel PMU LDO | 401 | G3H logic supply. If absent: PMU not starting – verify PP3V8_AON first. |
| PP1V8_AON | 1.8V | AON | Chapel PMU | 401 | AON 1.8V for SMC core. If absent: PMU fault – check Chapel IC pins. |
| PP5V_S5 | 5.0V | S5 | Chapel PMU Buck | 401 | S5 standby – USB-C enumeration. If absent: SMC not enabling S5 domain. |
| PP3V3_S5 | 3.3V | S5 | Chapel PMU LDO | 401 | S5 3.3V for ACE3 controllers. If absent: check PMU SLP_S5_L output. |
| PP1V8_S5 | 1.8V | S5 | Chapel PMU | 401 | S5 standby logic. If absent: S5 domain failure. |
| PP5V_S0 | 5.0V | S0 | Chapel PMU | 401 | Active 5V – sensors, fans. If absent: system not entering S0. |
| PP3V3_S0 | 3.3V | S0 | Chapel PMU | 401 | Active 3.3V – NVMe, PCIe. If absent: possible short on NVMe bus. |
| PP1V8_S0 | 1.8V | S0 | Chapel PMU | 401 | Active 1.8V I/O. If absent: verify PP3V3_S0 first. |
| PPVDD_CPU | 0.5–1.1V | S0 | SOC integrated VRM | 23 | CPU core voltage – dynamic. If absent: SoC not requesting power. |
| PPVDD_GPU | 0.5–1.0V | S0 | SOC integrated VRM | 23 | GPU core voltage. If absent: GPU block disabled or shorted. |
| PPVDD_SRAM | 0.75V | S0 | Chapel PMU | 25 | SRAM retention. If absent: memory init failure. |
| PPVDDQ_LPDDR5 | 0.5V | S0 | Chapel PMU | 29 | LPDDR5 memory VDDq. If absent: memory not initializing. |
| PP5V_USB_ATC | 5.0V | S0 | LT8642 / TPS62180 | 79, 87 | USB-C VBUS output. If absent: ACE3 not enabling – check PP3V3_S5. |
| PPVOUT_LCDBKLT | 38–55V | S0 | Backlight Boost IC | — | Display backlight boost. If absent: BKL_EN signal missing from SoC. |
| PP3V3_LCDVDD | 3.3V | S0 | Display Power LDO | — | eDP panel power. If absent: display flex or LDO failure. |
Power Distribution Tree
PPBUS_G3H (8–20V) ───────────────────────────────────────────────────────────────── │ ├── PP3V8_AON (3.8V) ← ICEMAN HP VR U3200 [Always-On domain] │ ├── Chapel PMU → PP1V8_AON (1.8V) [SMC/AOP core] │ └── Chapel PMU → PP3V3_G3H (3.3V) [G3H logic] │ ├── Battery Charger (Mandola MP) ← Page 52-53 │ ├── PPBUS_G3H charge path │ └── System Power Path switching │ ├── PP5V_S5 (5.0V) ← Chapel PMU [Standby domain] │ ├── PP3V3_S5 (3.3V) → ACE3 USB-C controllers │ ├── PP1V8_S5 (1.8V) → S5 logic │ └── PP_USB_VCONN → USB-C CC pins │ ├── PP5V_S0 (5.0V) ← Chapel PMU [Active domain] │ ├── PP3V3_S0 (3.3V) → NVMe, PCIe, sensors │ ├── PP1V8_S0 (1.8V) → Active I/O │ ├── PP5V_USB_ATC (5.0V) ← LT8642/TPS62180 → USB VBUS │ └── Fan Controllers → Page 68 │ ├── SOC VRMs (Integrated) ← Page 23-37 │ ├── PPVDD_CPU (0.5–1.1V) → CPU cores (dynamic) │ ├── PPVDD_GPU (0.5–1.0V) → GPU cores (dynamic) │ ├── PPVDD_SRAM (0.75V) → SRAM blocks │ ├── PPVDD_DCS (0.75V) → Display controller │ ├── PPVDDQ_LPDDR5 (0.5V) → Unified Memory │ └── PPVDD_AMPH / PPVDD_CIO → High-speed I/O │ └── Display Power ├── PP3V3_LCDVDD (3.3V) → Panel TCON ├── PPVOUT_LCDBKLT (38–55V) → LED backlight └── eDP lanes → LPDP from SoC (Page 7)
Key Components
| Reference | Designation | Function | Rails | Page | Common Failure Mode |
|---|---|---|---|---|---|
| U1000 | Apple M3 Max SoC (H15S) | System-on-Chip – CPU, GPU, Neural Engine, Memory Controller | Multiple VDD rails | 4–42 | Thermal damage, memory init failure, GPU block failure |
| U3000 | Chapel PMU | Power Management Unit – all rail sequencing | PPBUS_G3H input | 138, 400-404 | No power-on, stuck in S5, rail sequencing failure |
| U3200 | ICEMAN HP VR | 3V8 AON Buck Regulator | PPBUS_G3H → PP3V8_AON | 57 | No AON domain, PMU never starts |
| U5500 | ACE3 MagSafe Controller | MagSafe 3 PD negotiation & power path | PPBUS_G3H, PP3V3_S5 | 54–56 | No MagSafe charge, amber light only |
| U5600 | Mandola MP Charger IC | Battery charger – buck-boost topology | PPBUS_G3H | 52–53 | No charge, battery not detected |
| U7000/U7100/U7200 | ACE3 USB-C Controllers (×3) | USB-C PD, Thunderbolt 4 negotiation | PP3V3_S5, PP5V_S0 | 75–88 | Port not recognized, no Thunderbolt, no charge from USB-C |
| U7300 | LT8642 5V Regulator | USB-C ATC0/ATC1 VBUS supply | PPBUS_G3H → PP5V_USB | 79 | USB devices not powered |
| U7400 | TPS62180 5V Regulator | USB-C ATC2 VBUS supply | PPBUS_G3H → PP5V_USB | 87 | Right USB-C port no power |
| U8000 | HDMI Cobra Retimer | HDMI 2.1 signal conditioning | PP3V3_S0, PP1V8_S0 | 90–92 | No HDMI output, artifacting |
| U4000 | Secure Element (Juno) | Hardware security / Apple Pay | PP1V8_S5 | 50 | Touch ID failure, secure boot issues |
| U9000 | USB2 Repeater | USB 2.0 signal conditioning for all ports | PP3V3_S5 | 77, 85 | USB 2.0 devices not enumerating |
| U2000 | QSPI ROM | Firmware storage for SoC boot | PP1V8_S5 | 19 | Boot failure, recovery mode loop |
| U2100 | SEP ROM | Secure Enclave firmware storage | PP1V8_S5 | 19 | Security subsystem failure |
| Q3xxx | Fan Controllers | Dual fan PWM control | PP5V_S0 | 68 | Fans stuck at max speed, thermal shutdown |
Boot Sequence
| # | Signal / Rail | Expected Value | Condition | If Absent |
|---|---|---|---|---|
| 1 | PPBUS_G3H | 8–20V | Battery connected OR USB-C/MagSafe plugged | Check battery connector flex continuity; verify MagSafe/USB-C port integrity; inspect Mandola charger IC input path at U5600 pins 1-4. |
| 2 | PP3V8_AON | 3.8V | PPBUS_G3H present | ICEMAN HP VR U3200 not switching — measure EN pin; check inductor L3200 for open; verify PPBUS_G3H reaches U3200 input. |
| 3 | PP1V8_AON | 1.8V | PP3V8_AON stable | Chapel PMU U3000 not generating AON rails — check PMU input supply and crystal oscillator circuit. |
| 4 | SMC_RST_L | HIGH | PP1V8_AON present | SMC held in reset — verify reset controller output; check for short on SMC_RST_L net. |
| 5 | SMC_BC_ACOK | 3.3V | Charger IC detects valid input | Mandola charger IC not detecting adapter — measure ACIN pin voltage; verify MagSafe CC lines; check fuse in PPBUS path. |
| 6 | PM_SLP_S5_L | HIGH | SMC alive + ACOK received | SMC not exiting S5 — check SMC firmware (DFU recovery); verify PP1V8_AON stability; possible SMC hardware fault. |
| 7 | PP5V_S5 | 5.0V | PM_SLP_S5_L high | Chapel PMU S5 buck not enabled — verify SLP_S5_L reaches PMU; check for short on PP5V_S5 (measure resistance to GND, normal >10Ω). |
| 8 | PP3V3_S5 | 3.3V | PP5V_S5 stable | S5 3.3V LDO failure — verify PMU output; check ACE3 controller loads; measure resistance PP3V3_S5 to GND (normal >20Ω). |
| 9 | Power Button Press | LOW pulse | User presses power/Touch ID | Keyboard flex damaged — verify keyboard connection; test with known-good keyboard; check SMC_PWRBTN_L signal path. |
| 10 | PM_SLP_S4_L | HIGH | PMU receives power button event | System stuck between S5/S4 — verify NVMe SSD presence; check PP3V3_S5 to NVMe controller. |
| 11 | PM_SLP_S3_L | HIGH | Memory controller initializing | Memory init failure — possible bad LPDDR5 module (integrated, requires logic board replacement); verify PPVDDQ presence. |
| 12 | PP5V_S0 | 5.0V | PM_SLP_S3_L high | S0 5V rail missing — Chapel PMU not enabling S0 domain; check for short on PP5V_S0 bus (fans, sensors). |
| 13 | PP3V3_S0 | 3.3V | PP5V_S0 stable | S0 3.3V failure — possible NVMe short; disconnect NVMe flex and retest; measure PP3V3_S0 to GND resistance. |
| 14 | PPVDD_CPU | 0.5–1.1V | SoC requests VRM enable | CPU VRM not switching — SoC boot ROM failure; possible damaged SoC; verify PPVDD_CPU inductor with thermal camera. |
| 15 | PPVDD_GPU | 0.5–1.0V | GPU block enabled by SoC | GPU power missing — GPU block disabled by SoC (may still boot headless); check thermal paste contact. |
| 16 | CPU_PGOOD | HIGH | All VRM rails stable | PGOOD not asserted — one or more core rails missing; use thermal camera to find shorted VRM component. |
| 17 | PP3V3_LCDVDD | 3.3V | Display controller initialized | Panel power missing — check display flex connection; verify LDO enable signal from SoC. |
| 18 | PPVOUT_LCDBKLT | 38–55V | BKL_EN from SoC + panel detected | Backlight boost not running — BKL_EN low (verify with scope); boost IC fault; LED string open. |
| 19 | Display image | Apple logo | eDP link trained | No image despite backlight — eDP lane failure; display flex damage; LPDP controller issue in SoC. |
| 20 | macOS boot | Login screen | All rails stable, storage accessible | Boot loop / kernel panic — run Apple Diagnostics; check NVMe health; verify all connectors seated. |
6-Stage Progressive Diagnostic Engine
Work through stages in order. Complete each stage before unlocking the next. Measure rails at indicated test points with multimeter or oscilloscope.
1
Always-On Rails (G3H / AON Domain)
Expand ▼
2
Standby Rails (S5 / SMC Active)
🔒 Complete Stage 1 first
3
Active Rails (S0 / CPU Booting)
🔒 Complete Stage 2 first
4
Core Voltages (SoC CPU/GPU VDD)
🔒 Complete Stage 3 first
5
I/O & Display (Backlight / eDP)
🔒 Complete Stage 4 first
6
Peripheral / USB (Thunderbolt · Audio · Fans)
🔒 Complete Stage 5 first
No Power Diagnostic
A2991 No Power — Systematic Diagnostic Flow
The MacBook Pro A2991 (M3 Max) uses Apple Silicon with integrated power management. Unlike Intel Macs, there is no discrete SMC chip — the System Management Controller is integrated into the M3 Max SoC. The Chapel PMU handles all voltage rail sequencing.
Apple Silicon Note: The M3 Max SoC contains the SMC, AOP (Always-On Processor), and memory controller. A failure in any of these integrated blocks typically requires logic board replacement.
Step 1: Verify Power Source
- Connect known-good 140W USB-C charger or 96W MagSafe 3 adapter
- Check MagSafe LED: Amber = charging, Green = charged, No light = no communication
- If no MagSafe LED: try USB-C port directly (left ports share different ACE3 than right)
- Measure PPBUS_G3H at battery connector J5100 — expect 8–12V from battery or 14–20V from charger
Step 2: Check AON Domain
- Measure PP3V8_AON at C3200 — this is ICEMAN HP VR output
- If missing: check U3200 enable pin, inductor L3200, input capacitors
- Measure PP1V8_AON at C3001 — Chapel PMU AON output
- If PP3V8_AON present but PP1V8_AON missing: Chapel PMU not starting
X2681 PPBUS Missing — Charger Path Failure
Step 3: Charger IC Verification
- Locate Mandola MP charger IC U5600 (page 52-53)
- Verify ACIN pin receives voltage from MagSafe/USB-C
- Check SMC_BC_ACOK signal — should go HIGH when valid adapter detected
- Inspect for liquid damage around charger IC (common failure point)
Common A2991 Failure: Liquid spill near keyboard damages the charger IC and surrounding passives. Even if board looks clean, corrosion under ICs can prevent charging. Ultrasonic cleaning recommended before further diagnosis.
Step 4: MagSafe Controller Check
- MagSafe uses dedicated ACE3 controller U5500 (page 54-56)
- Verify PP3V3_S5 reaches U5500 — required for MagSafe enumeration
- Check MagSafe connector for bent pins or debris
- CC1/CC2 lines must be intact for PD negotiation
Step 5: Power Button Path
- Verify keyboard flex cable connected (keyboard required for power button)
- Test power button with multimeter — should short to ground when pressed
- Check SMC_PWRBTN_L signal reaches SoC
- If Touch ID flex damaged, power button may not function
Touch ID Pairing: The Touch ID sensor is serialized to the logic board. If you replace the keyboard top case, you MUST transfer the original Touch ID button to maintain functionality.
No Backlight Diagnostic
A2991 No Backlight — Display Power Analysis
The 16" MacBook Pro A2991 uses a Liquid Retina XDR display with mini-LED backlight. The backlight system uses a high-voltage boost converter to drive LED strings.
Flashlight Test
- Shine bright flashlight at screen angle in dark room
- If faint Apple logo or login screen visible: backlight circuit failure
- If nothing visible: display panel, TCON, or eDP link failure
Backlight Circuit Diagnosis
- Verify system enters S0 state (fans spin briefly, chime heard)
- Measure PPVOUT_LCDBKLT at boost IC output — expect 38–55V
- If missing: check BKL_EN signal from SoC (must be HIGH)
- Verify boost IC is switching — use oscilloscope on inductor node
X2681 Backlight Boost Circuit — IC and Inductor Check
Common Failure Points
- Display flex cable: Cracks at hinge fold area — inspect with magnification
- Boost IC: Shorted output MOSFET — measure output to GND resistance
- LED string: Open circuit in mini-LED array — requires panel replacement
- Liquid damage: Corrosion on backlight IC or connector pins
Parts Pairing Alert: Swapping displays between A2991 units causes display artifacting that cannot be resolved without Apple's Repair Assistant calibration software.
External Display Test
- Connect USB-C/Thunderbolt display or HDMI monitor
- If external display works: internal display or flex cable issue
- If no external display: GPU/LPDP controller failure in SoC
- Check HDMI Cobra retimer U8000 if HDMI specifically fails
Liquid Damage Recovery Procedure
A2991 Liquid Damage — Assessment and Recovery
Based on repair video analysis, the A2991 shows improved liquid resistance compared to older MacBooks, but keyboard spills still penetrate to the logic board. The dual-fan design creates airflow paths that can spread liquid contamination.
Initial Assessment
- Disconnect battery immediately — remove pentalobe screws, lift bottom case
- Locate battery disconnect lever and flex connector (T3 screws over trackpad connector first)
- Document liquid entry point and spread pattern
- Photograph all corrosion before cleaning
High-Risk Areas for A2991
- Keyboard area: Charger IC U5600, MagSafe controller U5500
- USB-C ports: ACE3 controllers U7000/U7100/U7200
- Fan intake areas: Sensors, thermal components
- Display hinges: Display flex cable, antenna connections
X2681 Corrosion Assessment — Ultrasonic Cleaning Protocol
Cleaning Procedure
- Remove logic board completely (requires T3, T5, T6, T8 drivers + 4.5mm standoff bit)
- Remove all shields and EMI covers
- Inspect under microscope for corrosion under ICs
- Ultrasonic clean: 5 minutes in isopropyl alcohol (99%+) at 40kHz
- Rinse with fresh IPA, air dry with compressed air
- Bake at 60°C for 2 hours to remove moisture
Post-Cleaning Verification
- Measure key rails resistance to GND before powering (see Short Circuit section)
- Power on with current-limited supply first (max 500mA)
- Monitor for excessive current draw indicating remaining short
- If successful, reassemble and test all functions
Cereal/Sugar Spills: As noted in repair videos, sugary liquids (Lucky Charms, soda, coffee) cause severe corrosion. These require aggressive cleaning and often component replacement.
Short Circuit Detection Methods
A2991 Short to Ground — Diagnostic Methods
Method A: DC Injection
Inject controlled voltage into shorted rail and use thermal camera or freeze spray to locate heating component.
| Rail | Injection Voltage | Current Limit | Max Duration | Injection Point |
|---|---|---|---|---|
| PPBUS_G3H | 3.0V | 2.0A | 30 sec | Battery connector J5100 positive |
| PP3V8_AON | 2.5V | 1.0A | 20 sec | C3200 capacitor pad |
| PP5V_S5 | 3.0V | 1.5A | 20 sec | C3100 capacitor pad |
| PP3V3_S5 | 2.5V | 1.0A | 20 sec | C3150 capacitor pad |
| PP5V_S0 | 3.0V | 1.5A | 20 sec | C3200 capacitor pad |
| PP3V3_S0 | 2.5V | 1.0A | 20 sec | C3250 capacitor pad |
| PPVDD_CPU | 1.0V | 3.0A | 15 sec | VRM inductor L1000 output |
| PPVDD_GPU | 1.0V | 3.0A | 15 sec | VRM inductor L1100 output |
Safety: Always use current-limited bench power supply. Never exceed listed voltages. Watch thermal camera continuously — stop immediately if component exceeds 80°C.
X2681 Short Detection — Thermal Imaging Method
Method B: Thermal Camera Detection
- Set bench PSU to injection voltage with current limit
- Connect positive to rail, negative to ground plane
- Observe thermal camera while slowly raising current limit
- Shorted component heats first — mark location
- Remove shorted component and verify rail resistance increases
Method C: Divide and Conquer
- Measure rail resistance to GND at multiple points
- Resistance decreases toward short location
- Remove suspect components one by one
- Retest resistance after each removal
- When resistance returns to normal, last removed component was short
Normal GND Resistance Values (Unpowered, 20°C)
| Rail | Normal Resistance | Shorted Indication |
|---|---|---|
| PPBUS_G3H | >50Ω | <10Ω |
| PP3V8_AON | >20Ω | <5Ω |
| PP5V_S5 | >15Ω | <5Ω |
| PP3V3_S5 | >20Ω | <5Ω |
| PP3V3_S0 | >15Ω | <5Ω |
| PPVDD_CPU | >2Ω | <0.5Ω |
| PPVDD_GPU | >2Ω | <0.5Ω |
Measurement Points Reference
| Signal / Rail | Test Point | Expected Value | Condition | Schematic Page |
|---|---|---|---|---|
| PPBUS_G3H | J5100 pin 1 (battery connector) | 8–20V | Battery or charger connected | 52 |
| PP3V8_AON | C3200 top pad | 3.8V | Always (power source present) | 57 |
| PP1V8_AON | C3001 top pad | 1.8V | Always (Chapel PMU alive) | 401 |
| PP5V_S5 | C3100 top pad | 5.0V | S5 standby state | 401 |
| PP3V3_S5 | C3150 top pad | 3.3V | S5 standby state | 401 |
| SMC_BC_ACOK | R3500 | 3.3V HIGH | Valid charger detected | 52 |
| PM_SLP_S5_L | Chapel PMU test point | HIGH | SMC exiting S5 | 401 |
| PP5V_S0 | C3200 top pad (fan supply) | 5.0V | S0 active state | 401 |
| PP3V3_S0 | C3250 top pad | 3.3V | S0 active state | 401 |
| PPVDD_CPU | L1000 output pad | 0.5–1.1V | CPU active (dynamic) | 23 |
| PPVDD_GPU | L1100 output pad | 0.5–1.0V | GPU active (dynamic) | 23 |
| PPVDDQ_LPDDR5 | C1300 top pad | 0.5V | Memory initialized | 29 |
| PP5V_USB_ATC | USB-C connector VBUS pins | 5.0V | USB device connected | 79 |
| PPVOUT_LCDBKLT | Backlight boost output cap | 38–55V | Display enabled | — |
| BKL_EN | Backlight IC enable pin | 3.3V HIGH | Display on | — |
Required Tools
Pentalobe P5
Bottom case screws (×8)
Torx T3
Internal connectors, Touch ID, flex brackets
Torx T5
Logic board screws, fan screws, hinges
Torx T6
Heat sink top screws
Torx T8
Display hinge screws
Standoff 4.5mm
Edge standoff screws (iFixit bit required)
Phillips P2
Wi-Fi antenna screws
Plastic Spudger
Flex cable disconnection, prying
Bent Tweezers
Precision screw placement, connector handling
Multimeter
Voltage/resistance measurements
Bench PSU
Current-limited DC injection (0–30V, 0–5A)
Thermal Camera
Short circuit detection, hot spot identification
Oscilloscope
Signal verification, PWM analysis
Ultrasonic Cleaner
Liquid damage cleaning (40kHz, IPA)
Hot Air Station
Component rework (250–400°C)
Microscope
Corrosion inspection, solder joint analysis
OpenBoardView
BoardView file analysis (.brd)
Isopropyl Alcohol 99%+
Cleaning, flux removal
Frequently Asked Questions
What is the most common failure on the MacBook Pro A2991 M3 Max?
The most common failure is liquid damage to the keyboard and charger circuit area. Spills penetrate through the keyboard and corrode the Mandola charger IC (U5600), MagSafe controller (U5500), and surrounding passives. This results in no charge or no power symptoms. Ultrasonic cleaning and often charger IC replacement are required.
Can I replace the display on A2991 without Apple's calibration tools?
No. Display swaps between A2991 units cause visible artifacting that cannot be resolved without Apple's Repair Assistant calibration software. The display is serialized to the logic board. Independent repair shops cannot currently perform display calibration without access to Apple's tools through the Self Service Repair program.
Is the SSD replaceable on the MacBook Pro M3 Max A2991?
No. The storage consists of 2 or 4 NAND flash modules soldered directly to the logic board. The storage capacity is determined at purchase and cannot be upgraded. If the flash storage fails, the entire logic board must be replaced, and data recovery requires specialized equipment to desolder and read the NAND chips.
How do I preserve Touch ID functionality when replacing the keyboard top case?
The Touch ID button is serialized to the logic board and must be transferred from the original top case to the new one. Remove the four T3 screws visible on the Touch ID bracket, then the rubber gasket to access two more T3 screws. Carefully push the button out and install it in the new top case. If the Touch ID button is damaged during transfer, Touch ID functionality is permanently lost.
What tools are required for A2991 logic board removal?
You need Pentalobe P5 (bottom case), Torx T3/T5/T6/T8, Phillips P2 (Wi-Fi antenna), and a 4.5mm standoff driver for the edge screws. An iFixit toolkit contains all necessary bits. Additionally, you need plastic spudgers for flex cable disconnection and bent tweezers for precision work. The repair is classified as expert-level due to the number of connections and risk of damaging serialized components.
Why does my A2991 show no MagSafe LED when plugging in the charger?
No MagSafe LED indicates the ACE3 MagSafe controller (U5500) is not communicating with the charger. First, verify the charger works with another device. Check the MagSafe connector for debris or bent pins. Measure PP3V3_S5 at the MagSafe controller — if absent, the S5 standby domain is not enabled. Common causes include liquid damage to U5500 or the charger IC U5600, or a failed Chapel PMU not generating S5 rails.
What is the estimated repair cost for liquid damage on A2991?
Repair costs vary significantly based on damage extent. Board-level cleaning and minor component replacement: $200–400. Charger IC or USB-C controller replacement: $300–500. If the M3 Max SoC or memory is damaged, logic board replacement is required at $1,200–2,500 depending on configuration. Apple's out-of-warranty repair for liquid damage typically costs $999–1,500. Always get a detailed diagnosis before committing to repair.