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Police Action Arcade: Endless Track Rotation & Index Sensor Alignment Guide

In the Police Action redemption game, the playfield features an endless conveyor-style illustrated road carpet that continuously moves beneath the miniature patrol car. To synchronize game cycles, score resets, and motor runtime, the main CPU relies on a Carpet Indexing IR Sensor that reads a dedicated indexing hole punched into the border of the carpet track.

 

When the carpet track keeps spinning endlessly without starting or ending a game cycle, the CPU has failed to detect the track's Home / Index Reference Point.

1. How the Carpet Indexing System Works

Plaintext

  [Motorized Conveyor Roller] ──> [Rotates Illustrated Carpet Track]
                                                 │
                                                 ▼
                       [Indexing Hole Punched in Track Edge Passes Through]
                                                 │
                                                 ▼
               ┌─────────────────────────────────┴─────────────────────────────────┐
               │              [Carpet Home IR Sensor (Photo-Interrupter)]           │
               │                                                                   │
               │   [IR Emitter LED] ─── (Invisible Beam) ───> [Photodiode Receiver]│
               └─────────────────────────────────┬─────────────────────────────────┘
                                                 │
                                                 ▼
                               [Index Signal Pulse Sent to CPU]

1. Continuous Rotation: The drive motor turns the conveyor roller, advancing the printed road carpet.

2. Optical Detection: As the carpet completes a rotation, a pre-punched physical hole on the edge of the carpet passes through a U-shaped IR sensor.

3. Pulse Trigger: The IR beam momentarily passes through the hole, triggering an electrical index pulse ($+5\text{V} \rightarrow 0\text{V}$) to the main CPU, confirming track alignment and cycle completion.

4. Fault Condition (Endless Spinning): If the sensor fails to detect the hole within a set time window, the CPU keeps the motor running indefinitely while searching for the missing home signal.

2. Common Root Causes

• Carpet Track Misalignment (Off-Track): Due to tension imbalance across the conveyor rollers, the carpet track shifts left or right over time. As a result, the physical indexing hole passes outside the IR sensor's optical gap.

• Dirty or Blocked Index Sensor: Dust, rubber belt fragments, or carpet lint cover the IR transmitter LED or photodiode receiver, preventing beam detection even when the hole aligns.

• Damaged or Torn Indexing Hole: If the punched hole becomes elongated, torn, or covered by adhesive tape, light cannot pass cleanly through it.

• Defective Index IR Sensor PCB: Failed photodiode, open current-limiting resistor, or damaged wiring harness to the mainboard.

3. Step-by-Step Adjustment & Repair Procedure

1.Remove Side Housing & Expose Track Edge:Mechanical Access.

Power off the cabinet. Disassemble the side maintenance cover adjacent to the carpet drive rollers to gain clear visual access to the edge of the carpet track and the mounted IR index sensor assembly.

2.Clean the Optical Sensor Lenses:Sensor Lens Cleaning.

Dip a cotton swab in 99% Isopropyl Alcohol (IPA) and clean both the emitter and receiver lenses inside the U-shaped sensor slot. Use compressed air to blow out loose debris from the track guide channel.

3.Manually Align the Carpet Hole to the Sensor Gap:Carpet Alignment.

Rotate the conveyor roller manually by hand until the physical indexing hole on the carpet edge reaches the sensor mounting bracket.

• Check if the hole passes dead-center through the U-shaped sensor gap.

• If the hole is offset to the left or right, loosen the conveyor roller tension bolts and shift the carpet track laterally until the hole aligns perfectly with the sensor contact point.

4.Adjust Conveyor Roller Tension:Tension Calibration.

Equalize the tensioning bolts on both sides of the drive roller. Proper roller balance prevents the carpet track from drifting sideways off its central tracking line during operation.

5.Verify Electrical Signal Toggling:Signal Test.

Apply power to the machine and connect a multimeter set to DC Voltage across Ground ($\text{GND}$) and the sensor's Signal OUT pin:

• Solid Carpet (Beam Blocked): Multimeter reads $+5\text{V DC}$ (or $0\text{V DC}$).

• Hole Centered in Sensor Slot (Beam Clear): Multimeter toggles sharply to $0\text{V DC}$ (or $+5\text{V DC}$).

If voltage does not toggle when the hole passes through, replace the IR sensor PCB module.

6.Perform Cycle Test in Service Mode:Operational Test.

Enter the machine setup menu and initiate a game cycle test. Verify that the carpet track stops or resets smoothy upon detecting the index hole without overshooting or continuously spinning.

Quick Reference Diagnostic Matrix

Symptom	Primary Cause	Action / Resolution
Track spins endlessly without stopping	Hole passing outside sensor path	Re-center carpet track on rollers; align hole to sensor slot.
Track stutters or stops at wrong location	Dirty optical lens or torn hole	Clean sensor with IPA; repair torn hole edge or punch clean new index hole.
Track doesn't spin at all	Blown drive motor fuse or belt snap	Check motor driver voltage ($+12\text{V}/+24\text{V}$) and inspect drive belt.
Error code on display (e.g., Err-Trk)	Index signal missing / Sensor dead	Verify signal toggling with multimeter; replace IR sensor PCB.

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