One 7-digit score display shows the wrong or flickering segments, and the fault moves with the display to any position. Reflowing the header pins helps only for a while.
Bally 7-digit display misbehaves wherever it is fitted: replace the decoder chip
Cause: The segment decoder chip on that display board had failed.
Checks
- Swap the display with another position to confirm the fault follows the display.
- Reflow the header pins and look for cracked joints near the decoder.
Fix
- Replace the decoder chip on the display board.
Bally displays use high voltage; unplug the game and let it discharge before handling the display.
Systems
Related tips
- Bally score display looks gassed with good voltages: replace its 4543 decoder chip
- Bally 6-digit display: one segment out on every digit, find the bad driver by swapping
- All displays show strange scores (one bad decoder)
- One display digit glitches and the fault follows the display: bad resistors
- Bally 6-digit display, whole digit dark: reflow header, check the 100k resistors
- Score display shows only a few numbers in display test: failed decoder chip
- Bally 6-digit display: the decoder chip should be E-620-38 (4543)
- One score display dark: poor contact at MPU J1 pin 20
Source: Pinball Repair help group!! (Facebook group)