Reseating a board or chip that then works is a warning
If reseating the interboard connector, a plug or a chip makes the game work, that connection has lost its gas-tight contact. Reseating only finds the fault; replace the connector or socket to fix it.
Systems
Related tips
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)