A large group of lamps does not work, sometimes with other lamps glowing bright and dim.
Many controlled lamps dead in a pattern
Cause: A lost lamp data line AD0-AD3 (shared by all four decoders) or a lost chip-select line PD0-PD3 (one decoder), usually at a connector pin; occasionally a PIA output stuck low.
Checks
- Mark the dead lamps on the lamp driver schematic and write their decoder output numbers in binary (AD0 is the right-hand bit). If one bit is 1 in every dead lamp, that AD line is lost.
- AD lines leave the MPU on J1 pins 15, 14, 13, 12 (AD0 to AD3, descending) and arrive at lamp driver J4 pins 14, 15, 16, 17 (AD0 to AD3, ascending).
- If lamps on the auxiliary lamp board are dead too, the fault is almost surely at MPU J1.
- If 16 lamps all on one decoder are dead, suspect that decoder's select line: U1 uses PD0, U2 uses PD1, U3 uses PD2 and U4 uses PD3.
Fix
- Reflow the header and repin the connector, or replace the PIA if the line is stuck at the MPU.
Systems
Related tips
- How Bally controlled lamps are powered and switched
- A controlled lamp that is always on means a shorted SCR
- LEDs flicker in controlled lamps on Bally and Stern SCR lamp boards
- Two inserts faintly lit all the time: failed lamp driver SCR
- One controlled lamp dead even after a new SCR: lamp driver board fault
- Controlled lamps flicker or stay out after fitting a replacement lamp driver with LEDs
- Some controlled lamps out: cold solder joint on the lamp driver board connector
- Controlled lamps stuck or not flashing: reflow MPU and lamp driver header pins
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)