How to Identify Pin 1 on an Arcade CPU, ROM, Socket, and Daughterboard

Learn how to identify Pin 1 on arcade CPUs, program ROMs, sockets, adapters, and daughterboards using notches, molded dots, board markings, socket orientation, and game-specific installation guides.

Correct Pin 1 orientation is essential when removing or installing a CPU, ROM, adapter, or daughterboard. A component installed backward may prevent the game from booting and can damage the component, the upgrade kit, or the original arcade PCB when power is applied.

This guide explains the most common Pin 1 markings and how to verify them before installation and first power-up.

Pin 1 Identification at a Glance

Disconnect cabinet power before removing or installing any component.
Look for a notch, molded dot, printed number, beveled edge, or PCB silkscreen marking.
Verify Pin 1 on the component, socket, PCB, daughterboard, and adapter.
Do not rely only on the direction of printed chip text.
Photograph the original orientation before removing a CPU or ROM.
Compare the installation with the game-specific guide.
Stop when markings are faded, hidden, damaged, or contradictory.
Complete a final Pin 1 check before restoring power.

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Why Pin 1 Matters DIP Notch Molded Dot Beveled Edge Socket Markings PCB Markings Square Pad Daughterboards Adapters Unclear Markings Checklist Support

Why Pin 1 Orientation Matters

Integrated circuits use numbered pins so each electrical connection reaches the correct circuit. Pin 1 establishes the starting point for the pin sequence and determines the component's proper orientation.

A CPU or ROM installed backward can place power and signals on the wrong pins. A daughterboard or adapter installed in the wrong direction can create the same problem across many connections at once.

Always identify Pin 1 before removing a component, again before reinstalling it, and once more before applying power.

The Notch on a DIP CPU or ROM

Many arcade CPUs and program ROMs use a dual in-line package, commonly called a DIP chip. These components often have a semicircular notch molded into one short end of the plastic body.

When the chip is viewed from above with the notch at the top, Pin 1 is normally the first pin on the upper-left side. Pin numbering then continues down that side, around the lower end, and back up the opposite side.

The notch is an orientation reference for the entire component. It should match the orientation shown by the socket, PCB silkscreen, daughterboard, adapter, and installation guide.

The Molded Dot or Circular Mark

Some chips use a small molded dot, dimple, circular depression, or printed dot near one corner instead of a clearly visible notch.

The corner nearest that mark normally identifies Pin 1. The mark may be very small, especially on older chips or components with faded surfaces.

Use strong, even lighting and view the chip from more than one angle. Reflections can hide a shallow molded dot or make a surface blemish look like an orientation mark.

Beveled, Indented, or Shaped Chip Ends

Some components use a beveled edge, shallow indentation, shaped end, or different molded texture to identify the Pin 1 end.

These markings can be less obvious than a standard notch. Dust, labels, age, and replacement markings may make the original shape difficult to see.

Do not assume that a slightly different edge is the Pin 1 indicator without comparing it with the socket, PCB marking, part type, and installation guide.

Pin 1 Markings on the Socket

Many DIP sockets have a notch molded into one short end. That notch usually matches the notch on the CPU or ROM installed in the socket.

A socket may also have a small molded number, dot, or Pin 1 indicator near one corner. Older sockets, replacement sockets, and stacked sockets may use different styles.

Socket orientation alone is not enough when the socket may have been replaced incorrectly. Confirm the marking against the PCB silkscreen and game-specific installation guide.

PCB Silkscreen and Printed Pin 1 Markings

The original arcade PCB may include a printed component outline with a notch at one end. It may also include a printed number 1, a dot, an arrow, or a small mark near the Pin 1 corner.

Board markings can be hidden beneath the socket or component, partially covered by repairs, or faded after decades of use. A replacement socket may also obscure the original outline.

Photograph the area before removing the CPU or ROM so the original component direction and surrounding markings are preserved for reference.

Square Solder Pads and Pin 1

On some PCBs, Pin 1 may use a square solder pad while the remaining pads are round. This can be useful when inspecting the solder side of the board.

However, not every board uses this convention, and previous repairs may have changed the pad shape or covered it with solder.

Treat a square pad as supporting evidence rather than the only source of orientation. Confirm it with the component, socket, PCB markings, and installation guide.

Pin 1 on an Arcade Daughterboard

A HighScoreSaves daughterboard normally installs into the original CPU socket, and the original CPU is normally installed on the daughterboard unless the product page and installation guide state otherwise.

The daughterboard may identify Pin 1 with a printed number, arrow, dot, notch outline, labeled corner, or installation-guide photograph.

Pin 1 on the daughterboard must align with Pin 1 on the original PCB socket. The CPU installed on the daughterboard must also match the daughterboard's CPU socket orientation.

Verify both levels separately. A correctly oriented daughterboard can still contain a backward CPU, and a correctly oriented CPU can still be installed on a backward daughterboard.

Pin 1 on Adapters and Multi-Board Assemblies

Some arcade kits use a game-specific adapter between the original PCB and the main daughterboard. Multi-board assemblies may also use ribbon cables or connectors with their own Pin 1 markings.

Each connection must be checked independently. Confirm Pin 1 from the original PCB to the adapter, from the adapter to the daughterboard, and from the daughterboard to the CPU or other component.

Follow the exact order and orientation shown in the game-specific installation guide. Do not assume that similar connectors all face the same direction.

Do Not Use Printed Chip Text as the Only Guide

The direction of the printed manufacturer name or part number is not a reliable Pin 1 indicator by itself. Printing can vary between manufacturers, production runs, replacement parts, and re-labeled components.

Use the physical notch, molded dot, board marking, socket marking, and installation guide rather than assuming that readable text should face a certain direction.

Photograph Orientation Before Removing a CPU or ROM

Before removing any socketed CPU or ROM, take one clear photo of the complete board and a close-up showing the component, socket, surrounding markings, and Pin 1 end.

The photo preserves the original orientation and helps identify the correct board location if several chips are removed during an installation.

Remove only the CPU, ROMs, or other components specifically identified by the game-specific installation guide.

When Pin 1 Markings Are Unclear

Stop before installation when the notch is damaged, the molded dot is hidden, the socket appears reversed, the PCB marking is covered, or different indicators seem to conflict.

Do not guess and do not use power to test the orientation. Applying power with a backward component can cause damage before the cabinet can be turned off.

Take clear photos of the complete PCB, component, socket, surrounding board markings, solder side, adapter, and daughterboard. Compare them with the product page and game-specific installation guide or send them to HighScoreSaves for review.

Final Pin 1 Checklist Before Power-Up

The cabinet is unplugged during installation.
Pin 1 has been identified on the original CPU or ROM.
Pin 1 has been identified on the PCB socket and silkscreen.
Pin 1 has been identified on the daughterboard.
Pin 1 has been identified on every adapter and ribbon-cable connection.
The component notch or dot matches the correct orientation.
The daughterboard orientation matches the original PCB socket.
The CPU orientation matches the daughterboard socket.
Every pin is straight and seated in the correct socket hole.
The completed installation matches the game-specific installation guide.
No uncertainty remains before power is restored.

Technical Support

If Pin 1 markings are faded, hidden, damaged, or contradictory, stop before installation or power-up.

Email is the preferred support method. Contact sales@highscoresaves.com and include clear photos of the complete PCB, component, socket, PCB markings, solder side, daughterboard, adapter, and surrounding area.

Always disconnect cabinet power before removing or installing a CPU, ROM, adapter, or daughterboard. Verify Pin 1 on the component, socket, PCB, daughterboard, adapter, and installation guide before applying power.