Clean battery corrosion off a CPU board

Steps

• Remove and discard the batteries.
• Cut out any green or gray damaged parts and sockets, leaving the legs; chips and transistors are hit hardest.
• Add fresh solder to each cut leg, heat it and pull it out; replace corroded header pins.
• If old solder will not melt, add new solder or clean it with a small wire wheel.
• Sand green and gray areas with 100-150 grit until the copper is bright; repair any trace sanded through.
• Scrub with a 50/50 vinegar and water mix, rinse with water, then rinse twice with 99% alcohol.
• Refit removed parts (not the battery), putting chips in good sockets; use flux on bare copper.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Move the CPU batteries off the board
• Check the battery blocking diode D17
• Battery holder looks fine but makes no contact
• Boots straight into the adjustments menu: corroded battery holder
• Lights up but dead after storage: leaked batteries on the board
• Replace batteries of unknown age right away
• Batteries drain in days or get hot
• Audit mode with under 3.6 V at the RAM

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)