Lamp always on: ground the SCR gate from TP2
Steps
- Game in display test. Clip a jumper to lamp driver TP2 (ground).
- Touch the gate of the SCR: the lamp should go out.
- If it stays on, test and replace the SCR.
- On a -14 board with an MCR106, ground the input of the CD4050 feeding it; if the lamp stays on the buffer is bad.
- Otherwise 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
- Prove the lamp wiring by grounding the SCR anode
- 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)