Board Voltages 2026-05-04

820-02521 Voltage Reference — MacBook Air M1 2020

Complete DC voltage map for the 820-02521 logic board under normal operating conditions across all power states (S5 standby, S0 active, and sleep modes). Use this reference to diagnose voltage rail failures, bootloop, and no-power conditions. All measurements taken at test points and via-probe under no-load conditions where noted; adjust for actual load conditions.

Main Voltage Rails

Rail Name	Power State	Expected Voltage	Measurement Point	Notes
`PP5V0`	S5 (Standby)	5.0–5.1 V	USB-C power input TP	Primary 5 V rail from USB-C; supplies most auxiliary circuits
`PP5V0`	S0 (Active)	5.0–5.1 V	USB-C power input TP	Should remain stable under load; ripple <100 mV typical
`PP3V3`	S5 (Standby)	3.25–3.35 V	U6500 output pin / main 3V3 bus	Generated from PP5V0 via primary buck; critical for all digital logic
`PP3V3`	S0 (Active)	3.25–3.35 V	U6500 output pin / main 3V3 bus	Must be stable; 50–75 mA typical current under load
`PP1V8_LOGIC`	S5 (Standby)	1.75–1.85 V	U6700 output / logic core rail	Generated from PP3V3; supplies SoC I/O, memory controllers
`PP1V8_LOGIC`	S0 (Active)	1.75–1.85 V	U6700 output / logic core rail	Typical 200–300 mA under full CPU load; tight tolerance required
`PP1V2_CORE`	S5 (Standby)	0 V	U6100 output (main VDD)	CPU core voltage; off during standby; enable via VDD_ENABLE signal
`PP1V2_CORE`	S0 (Active)	1.15–1.25 V	U6100 output (main VDD)	Primary M1 SoC core rail; 30–50 A typical under load; very dynamic
`PP0V85_SOC`	S5 (Standby)	0 V	U6200 output	SoC analog supply; off during standby
`PP0V85_SOC`	S0 (Active)	0.82–0.88 V	U6200 output	Supplies analog blocks within SoC; tight regulation required
`PP2V5_ANA`	S5 (Standby)	2.45–2.55 V	U7200 output / analog block	Analog supply for storage subsystem and audio codec
`PP2V5_ANA`	S0 (Active)	2.45–2.55 V	U7200 output / analog block	Remains on in all states; stable 5–10 mA load
`PP1V0_RAM`	S5 (Standby)	0 V	U6300 output	LPDDR4X supply; off during standby to save power
`PP1V0_RAM`	S0 (Active)	0.95–1.05 V	U6300 output	Memory core voltage; 3–8 A typical; tight tolerance
`PP1V2_RAM_TERM`	S5 (Standby)	0 V	U6350 output	LPDDR4X termination supply; off during standby
`PP1V2_RAM_TERM`	S0 (Active)	1.15–1.25 V	U6350 output	Termination for memory data lines; 1–2 A typical
`PP3V3_BT`	S5 (Standby)	3.25–3.35 V	U7500 output / Bluetooth module	Supplies Bluetooth/Wi-Fi combo module; always on for wake
`PP3V3_BT`	S0 (Active)	3.25–3.35 V	U7500 output / Bluetooth module	Typical 100–150 mA under Wi-Fi activity
`PP5V0_USB`	S5 (Standby)	5.0–5.1 V	USB-C connector, VBUS test pad	USB port power supply; gated via USB power delivery control
`PP5V0_USB`	S0 (Active)	5.0–5.1 V	USB-C connector, VBUS test pad	Can supply up to 3 A per port depending on PD contract
`PP3V3_NVME`	S5 (Standby)	3.25–3.35 V	U8100 output / SSD module	SSD supply; off in deep sleep, on in standby for fast wake
`PP3V3_NVME`	S0 (Active)	3.25–3.35 V	U8100 output / SSD module	Typical 50–200 mA depending on SSD activity
`PP1V8_NVME`	S5 (Standby)	0 V	U8150 output / SSD core	SSD core voltage; off in standby
`PP1V8_NVME`	S0 (Active)	1.75–1.85 V	U8150 output / SSD core	Typical 20–50 mA under I/O activity
`PP5V0_LIGHTING`	S5 (Standby)	0 V	Keyboard backlight FET gate / controller	Keyboard backlight supply; always off in standby
`PP5V0_LIGHTING`	S0 (Active)	4.9–5.1 V	Keyboard backlight FET gate / controller	PWM-controlled; 0–500 mA depending on brightness
`PP3V3_DISCRETE`	S5 (Standby)	3.25–3.35 V	Discrete GPIO power rail / sensor supply	Powers motion sensors, SMC peripherals; always on
`PP3V3_DISCRETE`	S0 (Active)	3.25–3.35 V	Discrete GPIO power rail / sensor supply	Typical 20–50 mA; used by accelerometer, gyro, ambient light
`PP1V2_CAM`	S5 (Standby)	0 V	U9100 output / camera sensor	Webcam analog supply; off during standby
`PP1V2_CAM`	S0 (Active)	1.15–1.25 V	U9100 output / camera sensor	Only on when camera active; typical 50–100 mA during video
`PPVCCIO_CAM`	S5 (Standby)	0 V	U9110 output / camera I/O	Webcam I/O supply; off during standby
`PPVCCIO_CAM`	S0 (Active)	1.75–1.85 V	U9110 output / camera I/O	Active when camera enabled; typical 30–60 mA

Key Enable Signals

Signal Name	Expected State (S5)	Expected State (S0)	Control Source	Notes
`SMC_ENABLE`	Low (0 V)	High (~3.3 V)	SMC / EC firmware	Master enable from System Management Controller; gates all major rails
`VDD_ENABLE`	Low (0 V)	High (~3.3 V)	SMC via U6100 EN pin	Main SoC core voltage enable; high impedance during standby
`VDD_ANA_ENABLE`	Low (0 V)	High (~3.3 V)	SMC via U6200 EN pin	SoC analog supply enable; gated independently
`VRAM_ENABLE`	Low (0 V)	High (~3.3 V)	SMC via U6300 EN pin	LPDDR4X supply enable; off in deep sleep for power saving
`NVME_ENABLE`	Low (0 V)	High (~3.3 V)	SMC via U8100 EN pin	SSD supply enable; may remain on in standby for quick wake
`BT_ENABLE`	High (~3.3 V)	High (~3.3 V)	SMC via GPIO line	Bluetooth module always powered for wireless wake; controlled by firmware
`CAM_ENABLE`	Low (0 V)	Low / High (~0–3.3 V)	SMC / SoC I2C control	Camera supply and I/O enable; gated only when actively in use
`LIGHTING_EN`	Low (0 V)	PWM (0–3.3 V)	SoC PWM output to FET gate	Keyboard backlight enable; PWM frequency ~1 kHz typical

Power State Voltage Summary

Power State	Description	Core Rails On	Peripheral Rails On	Typical Current Draw
S5	Standby (AC connected, battery present)	PP3V3, PP2V5_ANA, PP3V3_BT, PP3V3_DISCRETE	PP5V0, PP5V0_USB, PP3V3_NVME	<100 mA
S4	Hibernation / Memory Sleep (rare on M1)	PP3V3, PP2V5_ANA, VRAM (minimal)	PP3V3_DISCRETE, PP3V3_BT	50–80 mA
S3	Sleep (SoC/RAM clocks gated, displays off)	PP3V3, PP2V5_ANA, PP1V0_RAM (minimal)	PP3V3_BT, PP3V3_DISCRETE, PP3V3_NVME	80–120 mA
S0	Active / Full power	All rails	All rails	5–15 A (depends on CPU/GPU load)
G3	Mechanical off / Battery removed	None	None	0 mA (ideal); <5 µA leakage

Common Fault Voltages

Symptom	Rail(s) to Check	Expected Voltage	Fault Indication	Possible Cause
No power / board dead	PP5V0, PP3V3	5.0–5.1 V, 3.25–3.35 V	0 V on both rails	Dead main buck U6500, PMIC damaged, or USB-C connector fault
No USB power delivery / won't charge	PP5V0_USB, USB data lines D+/D−	5.0–5.1 V (negotiated)	0 V or floating	PD controller U7000 failure, USB-C port damage, or firmware issue
Won't boot / bootloop	PP1V2_CORE, PP0V85_SOC, PP1V8_LOGIC	1.15–1.25 V, 0.82–0.88 V, 1.75–1.85 V	0 V (never enabled) or oscillating (unstable)	SoC core buck U6100 dead, enable signal stuck low, or SoC damaged
Instant shutdown / kernel panic on load	PP1V2_CORE, VRAM (PP1V0_RAM)	1.15–1.25 V, 0.95–1.05 V	Voltage sags >150 mV under load or ripple >200 mV	Weak buck inductor, shorted capacitor, or excessive load (SoC short)
SSD not detected / NVME error	PP3V3_NVME, PP1V8_NVME, SSD_EN signal	3.25–3.35 V, 1.75–1.85 V, 3.3 V	0 V on either NVME rail or enable stuck low	SSD buck U8100/U8150 failure, enable signal not driven, or SSD module short
Wi-Fi / Bluetooth dead	PP3V3_BT, BT_EN signal	3.25–3.35 V, 3.3 V	0 V on PP3V3_BT or signal stuck low	Bluetooth module buck U7500 failure, enable signal not driven, or module damaged
Keyboard backlight won't turn on	PP5V0_LIGHTING, LIGHTING_EN PWM	4.9–5.1 V, 0–3.3 V PWM	0 V on rail or PWM always low	Lighting buck dead, FET gate driver U9200 shorted, or SoC PWM output dead
Camera won't enumerate / black video	PP1V2_CAM, PPVCCIO_CAM, CAM_EN	1.15–1.25 V, 1.75–1.85 V, 3.3 V	0 V on either supply or enable stuck low	Camera buck U9100/U9110 failure, I2C enable line stuck, or sensor damaged
RAM not detected / memory error on boot	PP1V0_RAM, PP1V2_RAM_TERM, VRAM_EN	0.95–1.05 V, 1.15–1.25 V, 3.3 V	0 V on either rail or enable stuck low	RAM buck U6300/U6350 failure, enable line stuck, or LPDDR4X module short
Random resets / watchdog timeout	PP1V8_LOGIC, PP3V3, SMC reset line	1.75–1.85 V, 3.25–3.35 V, 3.3 V	Sagging or oscillating voltage under load; reset line chattering	Weak logic buck U6700, shorted bulk capacitor, or SMC watchdog firmware issue
No USB ports work	PP3V3, USB controller supply (via U8000)	3.25–3.35 V	0 V or sagging to <3.0 V	USB controller buck failure or main 3V3 rail short
Audio codec no sound / no mic	PP2V5_ANA, PP1V8_LOGIC (codec I/O)	2.45–2.55 V, 1.75–1.85 V	0 V on either rail	Analog buck U7200 dead or codec power delivery issue
Display won't light / backlight dark	PP5V0, PP3V3 (display power)	5.0–5.1 V, 3.25–3.35 V	0 V on either rail or sagging under display load	Display power FET shorted, LVDS buck dead, or main 5V0/3V3 undersupplied

Notes & Caveats

Measurement technique: Use a high-impedance multimeter (10 MΩ+) on DC voltage mode. Probe power rails via test points or directly on buck output pins; avoid the SoC balls themselves (risk of micro-junction damage). For low-voltage rails (<1 V), use an oscilloscope to catch transients missed by slower multimeters.
Load state dependency: Most core rails (VDD, VRAM, SoC analog) exhibit significant voltage sag under full CPU/GPU load (±100–150 mV typical). A static measurement under no-load is not sufficient for diagnosing a loaded system; always measure during the specific failure condition (e.g., during boot, during a 3D benchmark).
Probe tip cleanliness: 820-02521 uses 0.4 mm pitch fine-pitch BGA and micro-vias. A dirty or oxidized probe tip will create false readings (typically 0.1–0.3 V lower than actual). Clean probe tips with isopropyl alcohol and inspect under magnification before critical measurements.
Temperature compensation: Voltage regulators on this board are calibrated for 25 °C. Thermal variations (especially around the SoC during heavy load) can shift output by ±50 mV. Avoid measuring immediately after thermal stress testing.
SMC sequencing: The SMC firmware enforces strict sequencing of rail enables. A rail showing 0 V when it should be on typically means the enable line from the SMC is stuck low or the SMC itself is not responding to power-on signals. Check SMC_ENABLE, VDD_ENABLE, and other gate signals before replacing bucks.