I've found out some interesting patents regarding these home model pinball machines.
The Brunswick/Briarwood machines, Wonder Wizard, Sentinel, and Phillips Electronics machines are using this patent (applies in particular to Brunswick Super Star machine):
Patent # 4,109,916
Title: "Pinball Game with Simultaneous Projectors" (one coil operating two or more devices)
Filed: May 17, 1976 ; Granted: August 29, 1978
Inventors: Jeffrey D. Breslow, Highland Park, ILL. and Eugene Jaworski, Park Ridge, ILL.
Assignee: Marvin Glass & Associates, Chicago, ILL.
Licensed to Brunswick Bowling and Billiards
Application # 687,402
Status is expired.
The Mattel "Las Vegas" pinball uses this patent:
Patent # 4,162,793
Title: "Game Scoring System"
Filed: March 27, 1978 ; Granted: July 31, 1979
Inventor: Gary J. Cummings, Torrance, Calif.
Assignee: Mattel, Inc., Hawthorne, Calif.
Application # 890,143
Status is expired.
Patent # 4,203,602
Ball used as the switch.
The Wico "Big Top" pinball uses this patent:
Patent # 4,438,930
Title: "Rollover Switch Apparatus"
Filed: August 28, 1981 ; Granted: March 27, 1984
Inventor: Albin Peters, Chicago, ILL.
Assignee: Wico Corp., Niles, ILL.
Application # 297,117
Status is expired.