How Do You Measure +5V at a Classic Arcade PCB?

By HighScoreSaves Technical Team

Reviewed and updated September 5, 2026

Correct power is one of the first things to verify when troubleshooting an original arcade PCB.

Many classic digital logic circuits operate from a nominal +5V supply, but measuring only at the cabinet power supply does not necessarily tell you what voltage is actually reaching the game board.

Wiring resistance, aging connectors, oxidized contacts, damaged edge connectors, fuse holders, and poor ground connections can all create voltage drop between the power supply and the PCB.

That is why a useful voltage check should include a measurement at the PCB while it is under normal load.

Why Measure +5V at the PCB Instead of Only at the Power Supply?

Electrical resistance exists throughout the path between the power supply and the arcade board.

The path may include:

• Power-supply terminals
• Cabinet wiring
• Fuse holders
• Intermediate connectors
• JAMMA adapters
• Edge connectors
• PCB edge fingers
• Ground connections

Under load, resistance in these connections can cause the voltage arriving at the PCB to be lower than the voltage present at the power supply terminals.

This effect is explained in more detail in Classic Arcade Power Supplies Explained: +5V, +12V, Ground, and Voltage Drop .

What Tool Do You Need?

A digital multimeter capable of measuring DC voltage is normally sufficient for a basic +5V check.

The meter should be set to a DC-voltage range appropriate for measuring approximately five volts.

Use probes in good condition. Fine or insulated probe tips can reduce the chance of accidentally contacting two adjacent pins at the same time.

Step 1: Identify a Verified Ground and +5V Location

Do not guess which PCB connection is +5V or ground.

Use the game's correct schematic, wiring diagram, operator manual, PCB markings, or other reliable documentation to identify the proper points.

Depending on the PCB, useful measurement locations may include:

• A labeled PCB test point
• The PCB edge connector
• A power connector
• A verified ground point
• The power pins of an appropriate logic IC

Component pin numbers and supply arrangements vary, so never assume the power pins of an unfamiliar IC without checking its documentation.

For help following PCB documentation, see What Is an Arcade PCB Schematic and How Do You Read One?

Step 2: Measure While the PCB Is Connected and Operating

A voltage measurement is most useful when the board is connected and drawing its normal operating current.

With the multimeter set to DC volts:

1. Connect or touch the black meter probe to a verified PCB ground point.
2. Touch the red probe to the verified +5V point.
3. Read the voltage displayed by the meter.
4. Keep the probes stable and avoid allowing either probe to slip across adjacent conductors.

The correct operating voltage and allowable tolerance should be determined from the documentation for the specific PCB. Do not assume that every vintage arcade board should be adjusted to exactly the same measured value.

Step 3: Compare the PCB Measurement With the Power-Supply Output

If necessary, compare the voltage at the PCB with the voltage at the low-voltage DC output terminals of the power supply.

The difference between those readings can provide useful diagnostic information.

Power Supply Voltage Is Higher Than PCB Voltage

A significant difference suggests voltage is being lost somewhere between the supply and the game board.

Possible causes include:

• Oxidized connector contacts
• Loose terminals
• Worn or damaged PCB edge fingers
• Heat-damaged connectors
• Corroded wiring
• Poor ground connections
• Damaged adapters or intermediate connectors

The condition of these connections is discussed in Arcade Edge Connectors Explained: Dedicated PCB Connectors, JAMMA, and Adapters .

Both Readings Are Low

If the voltage is already low at the power supply output, investigate the supply, its adjustment, the connected load, and the cabinet's power system according to the manufacturer's documentation.

Do not automatically increase the adjustment before confirming that the supply is operating correctly and that the board is intended to receive the resulting voltage.

The Voltage Changes or Is Unstable

A reading that changes significantly may indicate an unstable supply, intermittent wiring or connector resistance, a changing load, or another electrical problem.

Intermittent voltage can contribute to game resets, freezes, startup failures, or unpredictable operation.

Why You Should Not Simply Turn Up the Power Supply

Increasing the power-supply adjustment can sometimes raise the voltage measured at the PCB, but that does not mean it corrected the underlying problem.

If excessive voltage drop is being caused by a dirty or damaged connector, increasing the supply output may place unnecessarily high voltage elsewhere in the cabinet while the bad connection continues to generate resistance and heat.

The better approach is to determine why the voltage is different before making a significant adjustment.

Can Low +5V Cause an Arcade Game Not to Boot?

Yes. If the digital circuitry is not receiving appropriate operating voltage, the CPU, ROM, RAM, TTL logic, and other devices may not operate reliably.

Possible symptoms can include:

• No boot
• Repeated resets
• Freeze or lockup problems
• Corrupted graphics
• Intermittent operation
• Memory-test errors

These symptoms are not unique to voltage problems, which is why measuring the supply is an important diagnostic step rather than a complete diagnosis.

Related troubleshooting guides include:

• Arcade Game Won’t Boot After Installing an Upgrade Kit
• Why Does a Classic Arcade Game Keep Resetting?
• Why Does a Classic Arcade Game Freeze or Lock Up?

Measure Before and After Installation When Troubleshooting

When diagnosing a problem that appeared after installing an arcade upgrade kit, a known-good measurement from the original configuration can be useful.

If no earlier measurement exists, document the current voltage and verify the condition of the PCB connector, CPU socket, daughterboard seating, and other items involved in the installation before making unrelated changes.

Also follow the game-specific HighScoreSaves Installation Guide for the exact kit being installed.

Keep a Record of Your Measurements

Write down where the measurement was taken, the voltage observed, whether the game was operating normally, and whether the reading was taken before or after a repair or installation.

Good documentation makes it easier to identify changes and prevents repeated adjustments based on memory.

Measure at the Board, Then Diagnose the Cause

A +5V measurement at the arcade PCB provides more useful information than checking only the power supply because it shows what the board is actually receiving after the voltage has traveled through the cabinet wiring and connectors.

If the reading is incorrect, determine whether the cause is the supply itself, voltage drop in the wiring and connectors, a poor ground path, or another system problem before adjusting or replacing components.

Correct voltage is an important foundation for reliable arcade operation, but it should always be evaluated as part of the complete PCB and cabinet system.

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