After filing contacts, the game works worse or not at all.

Game stopped working after filing switches

Cause: Contacts filed at an angle no longer meet face to face, so the contact area is tiny and the switch fails.

Checks

• Close each filed switch and check the faces sit flat on each other.

Fix

• Refile with the contacts held in their natural closed position, not forced together.

Systems

• Electro-mechanical

Related tips

• Why EM switch contacts get dirty
• A switch blade has lost its contact
• New to EMs? Do not adjust switches that work
• Switch gap and adjustment targets
• Tighten a switch stack before adjusting it
• Adjust a leaf switch at the stack
• Cleaning leaf switch contacts
• Normally open, normally closed and make/break switches

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)