CPU pin 5 (VMA) shows no signal, but appears when the pin is lifted from the socket.

Missing VMA signal from corroded traces

Cause: Oxidation between the VMA trace and a neighbouring heavy trace was shorting them.

Checks

• Lift pin 5 and see if VMA returns.
• Inspect traces near pin 5 for corrosion.

Fix

• Clean the corrosion with a vinegar and water solution, sand it clean, and refit the CPU.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Version "3b" CPU boards have extra printer pins at CN3
• Replacement CPU board won't boot with the old processor: socket contact
• Other CPU jumpers and what they set
• Bench-testing a CPU board on +5 V
• CPU boards are only downward compatible
• CPU EPROM jumpers J4 and J5
• Wrong speech and sounds play for callouts: battery-corroded CPU board
• CPU board versions 520-5003-01, -02 and -03

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)