How 6803 feature lamps share SCR drivers

CPU-controlled lamps run on 11 VAC, made by center-tapping a 20.5 VAC winding into phases A and B (no rectifier or filter). Two lamps on opposite phases share one SCR, and each is lit only half the time, which is why they get about twice the usual 6 volts. The board has 45 SCRs (35 small 2N5060 and 10 larger MCR106-1), enough for up to 90 lamps and flashers.

Systems

• Bally 6803

Related tips

• Lamp driver SCRs on the CPU board
• Lamp driver SCR blew apart with a crack
• Some feature lamps out after the backbox was lowered
• Expected LED-strip results on lamp headers J10-J13
• An LED stays dark on a lamp header during the test
• What is on the 6803 CPU board
• The 19 solenoid driver transistors
• Electronic spares for 6803 board repair

Source: Repairing Bally 6803 Pinball Games from 1985 to 1989, Clay Harrell (pinrepair.com)