What Is an Arcade PCB Schematic and How Do You Read One?

By HighScoreSaves Technical Team

Reviewed and updated September 2, 2026

Quick Answer

An arcade PCB schematic is a diagram showing how the electronic components and signals on a game board are electrically connected. Unlike a photograph or physical board-layout drawing, a schematic organizes the circuit by function. It can show CPUs, ROMs, RAM, logic chips, power rails, connectors, video circuits, sound circuits, control inputs, and signal names. Reading one begins with identifying the correct game and PCB revision, then following component reference designators, pin numbers, signal names, and connections from one circuit section to another.

Arcade schematics are among the most useful technical documents available for original classic arcade hardware.

At first glance, however, a schematic can look intimidating: rectangles, triangles, pin numbers, component references, signal names, arrows, buses, power symbols, and lines spread across several pages.

The key is to understand that a schematic is not intended to look like the physical PCB. It is a map of the electrical relationships inside the circuit.

What Does an Arcade Schematic Show?

Depending on the game and documentation, an arcade schematic may show:

CPU circuitry;
program ROMs;
RAM;
address and data buses;
logic ICs;
clock circuitry;
reset circuitry;
video circuits;
sound circuits;
control inputs;
coin inputs;
power connections;
edge-connector pinouts;
board-to-board connections; and
other game-specific hardware.

A complex arcade board set can require many schematic sheets to document the complete system.

Is a Schematic the Same as a PCB Layout?

No.

A schematic shows electrical relationships.

A PCB layout, parts-placement drawing, or component-location diagram shows where components are physically located on the board.

A chip shown next to another chip on the schematic may be physically located somewhere else on the PCB.

When troubleshooting, the schematic helps determine what should be electrically connected, while a component-location drawing helps you physically find the part.

Start With the Correct Game and PCB Revision

Before following any circuit, verify that the schematic actually applies to the PCB in front of you.

Check information such as:

game title;
manufacturer;
PCB assembly number;
board-set number;
revision number or letter;
schematic revision;
copyright date; and
page or sheet number.

A different revision can contain changed component locations, connectors, jumpers, or circuitry.

See What Is an Arcade PCB Revision and Why Does It Matter? for the hardware-revision side of this process.

What Are Reference Designators?

Electronic components are usually identified by a short reference such as:

R for resistor;
C for capacitor;
D for diode;
Q for transistor;
U or another manufacturer-specific designation for integrated circuits;
J for connector or jack; and
other designations depending on the documentation.

The exact convention can vary.

A reference such as R23 identifies a particular resistor, while C14 identifies a particular capacitor. ICs may also be identified by board location rather than a simple sequential number on some classic arcade documentation.

How Are Arcade IC Locations Labeled?

Many classic arcade PCBs use location systems such as:

1A;
3F;
5E;
7H; or
similar grid-style references.

These locations help connect the schematic to the physical PCB.

For example, a ROM may be described by both its device type and its board location.

Location references become especially important when several chips use the same part number.

How Do You Recognize the CPU on a Schematic?

The CPU is typically shown as a large integrated-circuit symbol with many numbered pins.

Connected signals can include:

address lines;
data lines;
clock;
reset;
interrupt signals;
read/write control signals;
power; and
ground.

You do not have to understand every CPU pin before using the schematic. Begin by recognizing which major signals connect the processor to memory and support circuitry.

For processor fundamentals, read What Does the CPU Do on a Classic Arcade PCB? .

How Are ROMs Shown on a Schematic?

ROM devices appear as integrated circuits connected to address, data, control, and power signals.

Program ROMs are commonly connected into the CPU's memory system, while graphics or sound-related ROMs can appear in other functional sections.

The schematic can help show which signals must reach the device for it to operate.

See Original Arcade ROMs Explained .

How Is RAM Shown?

RAM devices also connect to address and data signals, but RAM can be read from and written to while the game operates.

Different RAM sections may serve different purposes, including general working memory, video-related memory, or other game-specific functions.

When a built-in test reports a RAM error, the schematic can help identify what other circuitry connects to the reported device.

Read Arcade RAM Explained .

What Are Address and Data Buses?

A processor communicates with memory and other hardware using groups of electrical signals.

The address bus helps identify which memory location or device the processor wants to access.

The data bus carries the actual data being transferred.

On a schematic, many related signals can be grouped into a bus rather than drawing every wire across the entire page.

Individual signals may be labeled with names such as A0, A1, A2 or D0, D1, D2, depending on the hardware.

What Does a Signal Name Mean?

A line on one part of the schematic may end with a signal label instead of continuing physically across the entire page.

If the same signal name appears elsewhere, the two points are electrically related according to the schematic even though a continuous line is not drawn between them.

This makes complex diagrams much easier to read.

What Does a Bar or Slash on a Signal Name Mean?

Digital schematics often identify signals that are active low.

Depending on the drawing convention, this can be represented by:

a line above the signal name;
a slash;
a leading symbol;
a trailing symbol; or
another notation explained by the documentation.

An active-low signal performs its asserted function when the electrical logic level is low rather than high.

The notation should be interpreted according to the convention used on that schematic.

How Do You Read Power on an Arcade Schematic?

Power rails may be shown using labeled symbols rather than lines running through every page.

Common examples on classic arcade hardware include +5V, +12V, ground, and other game-specific supply rails.

A component connected to a +5V symbol is electrically connected to that power network even if the schematic does not draw a wire all the way back to the cabinet power connector.

For arcade power fundamentals, see Classic Arcade Power Supplies Explained .

How Do You Find the Edge Connector on a Schematic?

The cabinet interface is usually represented by a connector symbol with numbered or lettered contacts.

Depending on the board, those contacts can carry:

power;
ground;
video;
sync;
audio;
joystick inputs;
buttons;
start switches;
coin inputs; and
other signals.

The schematic or pinout helps determine what each contact actually does.

This is particularly important with pre-JAMMA hardware where a physically similar connector does not imply the same pinout.

Read Arcade Edge Connectors Explained .

How Do You Follow an Arcade Video Circuit?

A useful method is to work in sections.

For video, begin by identifying the part of the schematic associated with:

graphics ROMs;
video RAM;
timing;
color generation;
RGB outputs;
sync; and
the cabinet connector.

Do not attempt to understand the entire board simultaneously.

For the final PCB-to-monitor path, see Arcade Video Signals Explained .

How Do You Follow an Arcade Sound Circuit?

Sound sections can contain:

a sound CPU;
sound ROMs;
sound-generating ICs;
digital-to-analog circuitry;
filters;
amplifiers;
volume controls; and
speaker-output connections.

Again, the exact design varies by game.

The schematic helps show how a sound command or audio signal moves through each stage.

See How Does Sound Work in a Classic Arcade Game? .

How Are Joysticks, Buttons, and Coin Inputs Shown?

Control inputs can be shown entering through a cabinet connector and then passing into PCB input circuitry.

The schematic can help trace a signal from the edge connector toward buffers, logic, or the processor interface.

This can be useful when a switch works mechanically but the PCB does not recognize the input.

For control fundamentals, read How Do Arcade Controls Work? .

What Do Page References and Sheet Numbers Mean?

Large arcade schematics are often divided across multiple pages.

A signal may leave one sheet and continue on another. Documentation can use arrows, page references, grid coordinates, or signal names to show where the circuit continues.

When a line seems to disappear, look for:

a signal label;
a page number;
a sheet reference;
a grid reference; or
a matching signal elsewhere in the manual.

What Is a Good Way to Read a Schematic for the First Time?

Instead of starting at the upper-left corner and trying to understand every symbol, use a specific question.

For example:

Identify the correct PCB and schematic revision.
Choose the circuit you want to understand.
Find the major component involved.
Identify its reference designator or PCB location.
Read the pin numbers and signal names.
Follow one signal at a time.
Note where signals continue to another page.
Compare the schematic with the physical PCB or component-location drawing.

This turns a large schematic into a series of smaller, understandable paths.

Schematic vs. Operator Manual vs. Installation Guide

These documents perform different jobs.

A schematic documents electrical circuitry.

An operator or service manual may include adjustment instructions, cabinet information, test procedures, parts lists, troubleshooting information, and schematics.

A HighScoreSaves installation guide explains how to install a particular upgrade on supported hardware.

An installation guide should not be replaced with a schematic, and a schematic should not be treated as game-specific upgrade instructions.

Browse the HighScoreSaves Installation Guides for game-specific kit installation documents.

How Can a Schematic Help With Upgrade Compatibility?

A schematic can help document the hardware architecture of a game, but it does not by itself guarantee upgrade compatibility.

A physical board can have:

a different revision;
replacement sockets;
factory changes;
previous repairs;
conversion modifications;
bootleg circuitry; or
other differences not represented by the schematic being viewed.

Before ordering an upgrade, verify the actual PCB.

See How to Identify Your Original Arcade PCB Before Ordering a Kit .

Game-Specific Kit Pages Are Still Important

Even when a schematic is available, use the game-specific product and installation information for the upgrade itself.

Examples include:

These pages provide the upgrade context, while original manuals, schematics, and installation guides provide different layers of technical information.

Key Takeaway

An arcade PCB schematic is an electrical map of the game hardware. It shows how processors, ROMs, RAM, logic, power, video, sound, controls, connectors, and other circuitry are connected.

The easiest way to read one is not to understand every symbol at once. First confirm that the schematic matches the correct board and revision, choose one circuit or symptom, identify the relevant components, and follow their signal names and pin connections one step at a time.

Used together with the correct service manual, component-location information, physical PCB inspection, and game-specific installation documentation, schematics are one of the most valuable resources for understanding original classic arcade hardware.

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