Police Action Arcade: Steering Control System & Sensor Repair Guide

In the Police Action redemption arcade machine, players pilot a miniature patrol car across an illustrated city playfield track (printed carpet/mat surface) to intercept targets and earn ticket rewards. The physical mini-car is propelled from beneath the playfield using a motorized magnetic drive carriage.

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When players turn the steering wheel left or right, an optical quadrature encoder assembly mounted on the steering shaft sends direction and speed data to the CPU, which subsequently moves the magnetic carriage underneath the mat.

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When the steering wheel becomes unresponsive or fails to turn the mini-car, the fault almost always lies in the IR optical encoder PCB assembly or its physical optical disc (plat wheel).

1. How the Optical Steering Sensor Functions

Unlike analog potentiometers, which wear out from constant friction, Police Action utilizes a non-contact Optical Encoder System:

Plaintext

[Steering Wheel Shaft] ──> [Slotted Encoder Disc (Plat Wheel)]
                                     │
                    ┌────────────────┴────────────────┐
                    ▼                                 ▼
         [IR Transmitter LED Pair]       [Photodiode / Receiver Pair]
                    │                                 │
                    └────────────────┬────────────────┘
                                     ▼
                    [Dual Quadrature Signals: A & B] ──> [Main Processor]

1. Slotted Encoder Disc (Plat Wheel): A thin metal or plastic disc with regularly spaced slots/holes mounted directly to the steering column.

2. Dual IR Sensor PCB: Features two pairs of infrared emitters and photodiode receivers (Photo-interrupters).

3. Quadrature Signal Processing:

   • Direction Detection: The two IR beam gaps are offset. Turning the wheel Clockwise (Right) causes Signal A to trigger before Signal B. Turning Counter-Clockwise (Left) causes Signal B to trigger before Signal A.

   • Speed & Angle Detection: The frequency of the pulses determines how quickly and far the steering wheel is being turned.

2. Common Causes of Steering Failure

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• Dirty / Obstructed Sensor Lenses: Dust, airborne grease, and rubber particulate coat the IR LED and photodiode lenses, preventing light from passing through the disc slots.

• Blown or Weak IR Transmitter LED: Over time, the internal semiconductor junction degrades, causing the IR beam to dim below the photodiode activation threshold.

• Misaligned or Bent Slotted Wheel: If the disc wobbles or rubs against the U-shaped sensor slot, it damages the photodiode or blocks the beam continuously.

• Failed Onboard Resistors / Buffer IC: Current-limiting resistors on the sensor PCB or signal buffer ICs on the drive board burn out or develop cold solder joints.

• Severed / Loose Harness Wires: The continuous rotation and vibration of the steering column can strain wire crimps at the 4-pin harness connector ($\text{VCC}, \text{GND}, \text{Signal A}, \text{Signal B}$).

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3. Step-by-Step Diagnostic & Repair Procedure

1.Inspect Mechanical Shaft Alignment & Disc Gap:Mechanical Check.

Remove the front steering column shroud. Turn the wheel fully left and right. Verify that the slotted encoder disc (plat wheel) spins smoothly through the center of the dual optical sensor slots without scraping or touching the sensor housing. Tighten any loose shaft set-screws.

2.Verify IR Emitter Beam Output:Optical Inspection.

Apply power to the machine. Point a smartphone camera (front camera preferred) directly into the sensor's U-shaped slot.

• Working Emitters: You will see two faint glowing purple/pink dots on your phone screen.

• Dead Emitters: No light output visible (indicates blown IR LEDs, broken $+5\text{V DC}$ supply trace, or open current-limiting resistor).

3.Clean Lenses & Encoder Disc Slots:Cleaning Step.

Dip a cotton swab in 99% Isopropyl Alcohol (IPA) and thoroughly clean both sides of the U-shaped sensor channel. Use compressed air to clean out any lint or debris clogging the slotted encoder disc openings.

4.Measure Quadrature Signal Outputs (Channel A & B):Voltage Test.

Set your digital multimeter to DC Voltage. Connect the black probe to Ground ($\text{GND}$) and check the output pins while slowly turning the steering wheel by hand:

• Channel A (Pin 3): Voltage should toggle rapidly between $+5\text{V DC}$ (unblocked slot) and $0\text{V DC}$ (blocked slot).

• Channel B (Pin 4): Voltage should toggle rapidly between $+5\text{V DC}$ and $0\text{V DC}$.

If one or both channel voltages remain static at $+5\text{V}$ or $0\text{V}$ while turning the wheel, that channel's photodiode or pull-up resistor is defective.

5.Component-Level Repair (Individual Parts Replacement):Repair Option A.

If a single channel fails and you have soldering equipment, replace the faulty components on the sensor PCB:

• IR LED Emitter: Standard $5\text{mm}$ or $3\text{mm}$ $940\text{nm}$ IR LED.

• Photodiode Receiver: $940\text{nm}$ NPN Phototransistor / Photodiode.

• Resistors: Replace burned $330\,\Omega$ emitter resistors or $10\text{k}\Omega$ signal pull-up resistors.

6.Unit-Level Replacement (Complete Sensor PCB Swap):Repair Option B.

If circuit traces are damaged, replace the entire 1-unit steering sensor module. Unplug the 4-pin harness, unscrew the 2 mounting bolts on the bracket, mount the new sensor PCB, and ensure the encoder disc sits perfectly centered inside the sensor slot gap before powering on.

Troubleshooting Reference Matrix

Symptom	Primary Suspect	Recommended Action
Car doesn't move left or right	Total loss of $+5\text{V DC}$ or dead dual IR LEDs	Check harness voltage; test emitters with smartphone camera; replace sensor PCB unit.
Car turns Left, but won't turn Right	Channel A or Channel B signal line dead	Test voltage toggling on Channel A & B pins; replace defective photodiode or repair wire crimp.
Car moves erratically or stutters	Dust in slotted wheel or loose encoder disc	Clean sensor with 99% IPA; tighten encoder disc set-screws onto steering shaft.
Steering works in test mode, fails in game	Magnetic carriage belt / motor under playfield	Inspect magnetic drive belt and motor driver board beneath carpet playfield mat.