Apple calls its motherboards logic boards, designs them itself and prints a board number on every one: 820- followed by digits. That number, more than the marketing name or the year, decides which schematic and boardview apply. Apple laptops also have their own naming conventions — model numbers, EMC numbers, model identifiers — and later boards add security hardware that changes how firmware faults are handled. This guide explains the numbers and what they mean for repair.
The numbers you will meet
| Number | Where | Example | Use |
|---|---|---|---|
| Logic board number | Printed on the board | 820-00244 | Schematics and boardviews |
| Revision letter | After the board number on older boards | 820-2915-B | Board revision |
| Model number | Bottom case | A1708 | Identifies the hardware family |
| EMC number | Bottom case, next to the model number | EMC 2978 | Distinguishes versions within a model number |
| Model identifier | System information | MacBookPro13,1 | Software identification |
| Schematic document number | On the schematic | 051-xxxx | The document itself |
820- board numbers
Older logic boards use four digits after the prefix, often followed by a revision letter: 820-2915-B. Newer boards use five digits: 820-00244. The number identifies the board design. The catalog collects them in the Apple 820- logic boards family, and Apple boards in general under Apple.
A model number such as A1708 can cover several logic boards — for example versions with different processors or with and without a Touch Bar — so the board number on the PCB is the only reliable way to choose documents.
Revision letters
On older boards, the letter after the number shows the revision: -A, -B and so on. Later boards often carry revision information elsewhere in the silkscreen. As on other brands, revisions can move parts and change circuits, so match them where you can. Matching documents to revisions is covered in How to Match a Boardview to Your Board Revision.
Schematic numbers
Apple's schematics carry their own document number, usually starting with 051-, and list the board number they belong to. When you find a schematic, check that its board number matches yours; the document number alone does not identify the board.
Apple's naming inside the schematic
Apple schematics use a distinctive naming style that is worth learning:
- Power rails start with PP, followed by the voltage and a state suffix: PP3V42_G3H is a 3.42 V rail present in the G3 "hot" state (always on with power connected), PPBUS_G3H is the main system rail.
- State suffixes such as G3H, S5, S3 and S0 tell you when the rail should be present.
- The SMC — the system management controller — plays the role that the EC plays on other laptops: power button, power sequencing, fans and battery. Its role in general is described in The Embedded Controller (EC): What It Does.
Once you read these names, an Apple schematic becomes very systematic: the rail name tells you its voltage and when to expect it.
T2 boards
Intel-based MacBooks from around 2018 onwards contain the T2 security chip. It handles secure boot, storage encryption and parts of system management, and it has its own firmware. Consequences for repair:
- storage is soldered and encrypted; data recovery depends on the board working;
- some firmware problems are fixed by reviving or restoring the T2 firmware from another Mac, rather than by programming a flash chip directly;
- the classic approach of writing a BIOS dump with a programmer no longer covers everything.
Apple silicon boards
Apple silicon MacBooks integrate processor, graphics, memory and much of the system management into one package. Their firmware is also restored or revived through another Mac in a special mode rather than by programming chips. Board-level power diagnosis still works the same way — rails, enables, shorts — but more of the board's behaviour depends on firmware and on parts that cannot be replaced individually.
Common logic board fault areas
Across generations, a few areas appear again and again in MacBook repairs:
- Liquid damage — Apple boards are dense and liquid spreads under parts quickly. Corrosion near the keyboard and trackpad connectors, the SMC and the power section is frequent.
- Shorted main and always-on rails — the system rail and the always-on rails feed many parts; a single shorted capacitor stops the board.
- Backlight circuits on certain generations, where a fuse or the backlight driver fails.
- Charging — on USB-C models, the ports and their controllers; on older models, the charging connector and its circuit.
- Display cables that wear at the hinge on thin models.
These patterns are generation-specific; a board number makes it much easier to find what others have seen on the same design.
Data and repair decisions
On boards with soldered, encrypted storage — T2 and Apple silicon — the data on the laptop is tied to the logic board. Replacing the board means losing the data unless it has been backed up. That changes the value of a board-level repair: for many owners, getting the original board working long enough to recover data is worth more than the repair itself. Discuss this with the owner before choosing between repair and replacement.
Tools that help on Apple boards
Apple logic boards are dense and use many very small parts, so a good microscope and fine tips matter even more than usual. A USB-C power meter shows quickly whether a USB-C MacBook negotiates power and how much it draws as it starts. For firmware work on T2 and Apple silicon boards, a second Mac and a suitable cable replace the chip programmer used on other laptops. And because rail names encode their voltage and power state, a list of expected rail values per board number is easy to build and very useful.
Practical tips
- Photograph the board number and any revision marking before starting.
- Note the model number and EMC number from the bottom case.
- Check the schematic's board number against the board, not just the model name.
- Learn the rail naming — PP rails and state suffixes make Apple schematics quick to navigate.
- On T2 and Apple silicon boards, keep a working Mac and a suitable cable at hand for firmware revive and restore.
Board numbers in general are covered in Laptop Board Codes Explained: LA-, NM-, DA0, 6050A and 448 Numbers, and you can identify a number quickly with the Laptop Board Code Decoder.
Example: same model number, different board
Two laptops share the model number A1708. A schematic for one arrives labelled with that model number, but its board number differs from the one printed on the second laptop's logic board — the two are versions with different processors. The power sequence pages differ in several places. With the schematic matching the second board's 820- number, the missing rail is traced to its regulator in minutes.
FAQ
Where is the 820- number on a MacBook?
Printed on the logic board, often near an edge or a connector.
Is the model number enough to find a schematic?
No. One model number can cover several logic boards. Use the 820- number.
What does PP3V42_G3H mean?
A 3.42 V power rail present in the G3H state — whenever power is connected, even with the laptop off.
What is the SMC?
Apple's system management controller, which handles power, fans and battery like an EC on other laptops.
Can I reprogram a T2 or Apple silicon board with a chip programmer?
Not in the same way as older boards. Their firmware is usually revived or restored through another Mac.
Bottom line
Identify a MacBook logic board by its 820- number and revision, not by the model or EMC number alone. Check schematics by board number, learn Apple's PP rail naming and state suffixes, and treat T2 and Apple silicon boards as firmware-dependent systems where revive and restore replace chip programming.