What Do Resistors, Capacitors, and Diodes Do on a Classic Arcade PCB?

By HighScoreSaves Technical Team

Reviewed and updated September 6, 2026

CPUs, ROMs, RAM, and TTL logic often receive most of the attention on a classic arcade PCB, but those integrated circuits depend on many smaller components surrounding them.

Resistors, capacitors, and diodes appear throughout arcade hardware in power circuits, digital logic, audio systems, video sections, reset circuits, clock circuits, control inputs, and many other areas.

Understanding their basic jobs makes arcade schematics easier to read and helps explain why a small component can sometimes affect an entire section of the game.

What Does a Resistor Do?

A resistor limits or controls electrical current and can also be used with other components to establish voltage levels.

Resistors appear in many different parts of an arcade PCB, so there is no single job performed by every resistor.

Depending on the circuit, a resistor may:

• Limit current
• Create a voltage divider
• Establish a pull-up or pull-down condition
• Set amplifier gain
• Bias an analog circuit
• Work with a capacitor in a timing or filter network
• Protect or isolate another component

What Are Pull-Up and Pull-Down Resistors?

Digital inputs should normally have a defined logical state rather than being left electrically undefined.

A pull-up resistor connects a signal toward the positive logic supply so that the line tends toward a known HIGH state when nothing else is actively driving it.

A pull-down resistor performs the opposite function, tending to hold a line LOW.

These arrangements are common in digital electronics and may be used with switches, control inputs, reset circuits, and other logic signals.

This connects directly with the operation of TTL and 74-series logic chips found on many classic arcade PCBs.

What Is a Resistor Network?

Some arcade PCBs contain resistor networks or resistor packs that place several resistors into one physical package.

These devices can save board space and may provide groups of pull-up resistors, matched resistor values, or other repeated functions.

A resistor network can therefore affect multiple signals at once depending on how it is connected.

Its internal arrangement should be verified from the schematic, component information, or correct replacement documentation before substitution.

What Does a Capacitor Do?

A capacitor stores electrical charge and can respond differently to steady DC voltage and changing electrical signals.

That makes capacitors useful in many different arcade circuits.

Depending on the location, a capacitor may be used for:

• Power-supply filtering
• Local power decoupling
• Signal coupling
• Timing
• Noise suppression
• Audio filtering
• Reset circuits
• Video or analog circuitry

What Are Decoupling Capacitors?

Many arcade PCBs place small capacitors close to digital ICs.

These are often called decoupling or bypass capacitors.

Digital chips can draw very short bursts of current as their internal circuits change state. Local decoupling capacitors help stabilize the supply near the IC and reduce electrical noise on the power rail.

A board may contain many apparently identical small capacitors because each one supports the operation of nearby circuitry.

Their relationship to the PCB power system is covered by the broader concepts in Classic Arcade Power Supplies Explained .

What Is a Filter Capacitor?

Larger capacitors are often used in power circuits to reduce ripple or fluctuations in a DC supply.

Capacitors can charge when voltage rises and release stored energy when the voltage falls, helping smooth the supply.

The exact role depends on where the component is placed. A capacitor in a power section should not automatically be assumed to perform the same job as one in an audio or timing circuit.

Why Are Capacitors Used in Audio Circuits?

Audio signals continuously change voltage, which makes capacitors useful for coupling and filtering.

A coupling capacitor can allow the changing audio portion of a signal to pass between circuit stages while blocking a steady DC component.

Capacitors can also work with resistors to shape frequency response or establish amplifier behavior.

For the complete arcade audio path, see How Does Sound Work in a Classic Arcade Game?

Capacitors Can Also Be Part of Timing Circuits

A resistor and capacitor used together can create a time-dependent electrical response.

This can be useful in reset circuits, pulse generation, filtering, delay circuits, oscillators, and other timing-related functions.

Not every arcade timing signal is generated this way, but resistor-capacitor networks are common building blocks in electronics.

For broader digital timing concepts, see What Is the Clock Circuit on a Classic Arcade PCB and What Does It Do? .

Electrolytic Capacitors Have Polarity

Many electrolytic capacitors are polarized, meaning their positive and negative connections matter.

Installing a polarized capacitor backward can cause the circuit to operate incorrectly and may damage the component.

Orientation markings on the original part, PCB silkscreen, schematic, and replacement component documentation should all be checked when servicing a board.

Do not assume that every capacitor on the PCB is polarized. Ceramic and several other capacitor types are commonly non-polarized.

What Does a Diode Do?

A diode allows current to flow much more readily in one direction than the other.

That basic characteristic allows diodes to perform many useful jobs.

Depending on the arcade circuit, a diode may be used for:

• Rectification
• Reverse-polarity protection
• Signal isolation
• Clamping or protection
• Steering signals
• Switch or coil-related protection
• Voltage-reference functions with specialized diode types

Diode Orientation Matters

Because a diode is directional, installing one backward changes how current can flow through the circuit.

Diodes commonly include a body marking that identifies one end, and schematics use a directional diode symbol.

The correct orientation should be verified from the original board and documentation before replacement.

How Do These Components Appear on an Arcade Schematic?

Schematics normally identify components with reference designators.

Common examples include:

• R for resistor
• C for capacitor
• D for diode

The reference designator usually includes a number so the individual part can be identified, such as R23, C17, or D4.

The schematic may also show the resistance, capacitance, polarity, diode type, or other information needed to understand the part.

Learn how reference designators and circuit sections work in What Is an Arcade PCB Schematic and How Do You Read One? .

What Does a Burned Resistor Mean?

A visibly burned resistor is important evidence, but it does not automatically mean that replacing the resistor will repair the board.

A resistor may overheat because another fault caused excessive current to flow through it.

Replacing the visibly damaged component without determining why it overheated can result in the replacement failing again.

The surrounding circuit should be examined before power is reapplied.

Does Every Old Capacitor Need to Be Replaced?

Age alone does not identify the cause of a specific PCB fault.

Some types of capacitors can degrade with age, heat, electrical stress, or storage conditions, but replacing every capacitor on a board should not be treated as a substitute for troubleshooting.

The symptom, schematic, measurements, component type, location, and condition of the circuit should guide the repair.

This is particularly important on original arcade PCBs where unnecessary component replacement can damage pads, traces, or historically original parts.

Can a Small Passive Component Stop an Entire Arcade Game?

Yes, depending on its function.

A resistor in a reset network, capacitor in a timing circuit, diode in a supply path, or failed decoupling component can influence circuits much larger than the individual part itself.

That does not mean every no-boot or freeze problem is caused by a resistor, capacitor, or diode. It means that these components are part of the complete circuit and should not be ignored simply because they are smaller than the CPU or ROMs.

How Do Resistors, Capacitors, and Diodes Work With Digital ICs?

Integrated circuits rarely operate alone.

A CPU needs stable power, clock and reset circuitry, memory, logic signals, and correctly defined inputs.

Resistors can establish signal states, capacitors can stabilize supplies or create timing behavior, and diodes can steer or protect signals.

These supporting parts work alongside CPUs , ROMs , RAM , and digital support logic.

Diagnose the Circuit, Not Just the Component

A resistor, capacitor, or diode should be understood according to its role in the particular circuit.

The same component type can perform completely different jobs in the power, sound, video, clock, reset, or input sections of an arcade PCB.

Use the correct schematic, identify the surrounding circuit, verify component values and orientation, and determine why a part may have failed before replacing it.

Understanding these basic components makes the rest of the arcade PCB easier to understand because they support nearly every major subsystem on the board.

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