Technical terms used in board-level electronics repair — voltage rails, ICs, diagnostic techniques,
protocols and Apple-specific concepts. New entries are added regularly.
Voltage Rails
| Term | Definition |
|---|
| PP1V8_S3 | 1.8 V rail enabled in S3 suspend state |
| PP3V3_G3H | 3.3 V always-on rail derived from PPBUS_G3H |
| PP3V3_S3 | 3.3 V rail enabled in S3 suspend state |
| PP3V3_S5 | 3.3 V rail present in soft-off (S5) state |
| PP3V42_G3H | 3.42 V always-on rail that powers the SMC chip |
| PP5V_S5 | 5 V rail present in soft-off (S5) state |
| PPBUS_G3H | Apple's main always-on power bus, typically 12.5–12.6 V |
| PPBUS_S5_HS | PPBUS high-side after the main power switch |
| PPVCORE_S0 | CPU core voltage, present only in S0 active state |
| PPVRTC_G3H | 3.0–3.3 V RTC keep-alive rail for the SMC/RTC |
Power States
| Term | Definition |
|---|
| G3 (Mechanical Off) | Complete power-off: no voltage rails active |
| S0 (Active) | Fully active state: all rails up, CPU running |
| S0ix | Modern low-power idle state used by Apple Silicon |
| S3 (Sleep) | Sleep/suspend: RAM powered, CPU halted |
| S4 (Hibernate) | Hibernate: RAM contents saved to disk, minimal power |
| S5 (Soft Off) | Soft-off: only always-on rails active, awaiting power button |
ICs ICs & Chips
| Term | Definition |
|---|
| CD3215 / CD3217 | USB-C power delivery controller by Texas Instruments |
| INA3221 | Triple-channel current/voltage monitor used by Apple's SMC |
| ISL6259 | Charger IC used on Intel MacBooks, manages battery charging |
| ISL6264 | CPU core VRM controller on Intel MacBook Pro |
| ISL9239 | Multi-phase charger IC on later Intel and early Apple Silicon MacBooks |
| LP8550 / LP8558 | Backlight driver IC controlling display brightness |
| NCP81239 | Multi-phase GPU power controller used on NVIDIA/AMD GPUs |
| SMC | System Management Controller — Apple's embedded power/thermal manager |
| T2 Chip | Apple's security and system management chip on 2017–2020 Intel Macs |
| T6002 / T6022 | Apple BMIC (Battery Management IC) on Apple Silicon MacBooks |
| TPS51125 | Dual-phase synchronous buck converter for DDR/CPU rails |
Techniques Techniques
| Term | Definition |
|---|
| Cold Solder Joint | Brittle solder connection with high resistance, often from thermal cycling |
| DC Injection | Applying low-voltage DC to locate short circuits by heat |
| Diode Mode | Multimeter measurement mode used to check semiconductor junctions |
| Pad Lifting | PCB trace pad detaching from the board during desoldering |
| Reballing | Removing and re-applying BGA solder balls to an IC |
| Reflowing | Re-melting existing solder joints to restore cold solder connections |
| Resistance to GND | Measurement comparing a rail or pin resistance to the ground plane |
| Ultrasonic Cleaning | Using ultrasonic vibration in IPA to remove corrosion and flux residue |
| Underfill | Epoxy applied under BGA chips to reinforce mechanical bonding |
Protocols Protocols
| Term | Definition |
|---|
| I2C | Two-wire serial bus (SDA + SCL) used for inter-IC communication |
| JTAG | Boundary-scan debug interface used for chip-level debugging |
| One-Wire | Apple's proprietary single-wire protocol for MagSafe/charger identification |
| SMBus | System Management Bus — I2C derivative used for battery and power comms |
| SPI | Serial Peripheral Interface — fast 4-wire bus for flash chips and sensors |
| USB Power Delivery | USB-PD protocol for negotiating charging voltage and current over USB-C |
Board Concepts
| Term | Definition |
|---|
| ACOK | AC OK signal — tells the SMC that a valid charger is connected |
| BGA | Ball Grid Array — IC package where connections are solder balls on the underside |
| Boardview | Software file format (.brd/.bvr) showing PCB component placement |
| Decoupling Capacitor | Capacitor placed near an IC to filter supply noise and transients |
| Ground Plane | Copper layer connected to GND, providing reference and shielding |
| LDO | Low-Dropout Regulator — linear regulator with minimal input/output difference |
| MOSFET | Transistor used as a switch or amplifier in power circuits |
| PWM | Pulse Width Modulation — technique used to regulate power converters |
| Power Sequence | Ordered chain of rail enable events from G3H up to S0 |
| VRM | Voltage Regulator Module — converts input voltage to precise CPU/GPU supply |