Before removing the processor board, check the following areas:
- Verify optic alignment
- Use input test to verify if the phototransistor is good (use a flashlight to simulate a LED)
- Verify that the bill validator door switch is closed
- Test for – 8 to 10 VDC across J/P 170
- If the door LED is nonfunctional, then remove and replace LED
- If that doesn’t work, try the following steps:
Replace the processor board with a “known good” one
- If the processor board seems bad, check eBay for replacement or repair service
- If the processor board is good, then replace the motherboard
- To repair the motherboard, use this diagram to isolate the bad trace
- If the motherboard and processor board are good, then use this diagram to test for wire continuity

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