The game resets at random; sometimes it runs for days, sometimes only minutes. The +12 V supply sags well below normal.

Random resets, days or minutes apart: burnt power supply AC input connector

Cause: The AC input connector on the power supply board had burnt and was running hot (around 60 C), so the supply dropped out intermittently. The logic resets when the 12 V line falls too low.

Checks

• With the game running a while, feel the power supply connectors (carefully) or use a thermal camera; a hot connector is the culprit.
• Look for darkened header pins or a browned housing at the AC input plug.
• Watch the +12 V test point for dips.

Fix

• Replace the connector housing, its pins, and the header pins on the board for the AC input.

The power supply connectors carry transformer AC; turn the game off and unplug it before handling them.

Systems

• Williams System 11B

Games

• Cyclone

Related tips

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• Mystery wheel won't turn and its opto never registers: reflow the power supply headers
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• Low +5 V (below 4.9 V) from the power supply
• GI lamps out, game dark: burnt power supply connector 3J8 (pre-Banzai Run)
• GI connectors left the power supply after Cyclone
• What the System 11 power supply board feeds

Source: Pinball Repair help group!! (Facebook group)