Lamp always off: trigger the SCR gate from TP3
Steps
- Game in display test. Clip a jumper to lamp driver TP3 (feeds R70, 2K).
- Touch the SCR gate: the left leg of an MCR106, the centre leg of a 2N5060. The lamp should light.
- If not, test the SCR off-power on diode test and replace it if bad.
- On a -14 board with an MCR106 that tests good, replace the CD4050 buffer feeding it.
- Still dark: replace the 4514 decoder for that SCR.
This check is done with the game on; keep fingers off the line-voltage wiring and the high-voltage display circuit.
Systems
Related tips
- A controlled lamp that is always on means a shorted SCR
- Test lamp SCRs with the power off
- Substitute SCRs for the lamp driver board
- Lamp driver board layout: SCRs, decoders and connectors
- Lamp driver board: which SCR drives which connector pin
- LEDs flicker in controlled lamps on Bally and Stern SCR lamp boards
- AS-2518-14 vs AS-2518-23 lamp driver boards
- Lamp driver, auxiliary lamp driver and display driver test points
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)