One score display shows garbled or partial digits that look like a gassed glass, and the fault follows the display when it is swapped. The display test points read 5 V and about 180 V, and cleaning and reflowing the header pins made no difference.
Bally score display looks gassed with good voltages: replace its 4543 decoder chip
Cause: The 4543 segment decoder chip on the display board had failed (it was badly rusted); the glass itself was fine.
Checks
- Swap the display with another position to see if the fault follows it.
- Measure the display's 5 V and high voltage at its test points.
- Inspect the 4543 decoder and the display's resistors for corrosion.
Fix
- Replace the 4543 decoder chip on the display board.
- While there, members recommend fitting half-watt versions of the six 100k resistors and reflowing the header pins.
The display boards carry about 180 V DC; unplug the game and let the supply discharge before handling them.
Systems
Related tips
- Bally 6-digit display: one segment out on every digit, find the bad driver by swapping
- Bally 6-digit display, whole digit dark: reflow header, check the 100k resistors
- Bally 7-digit display misbehaves wherever it is fitted: replace the 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
- Garbled displays: broken pin in the MPU display connector
- All digits on all displays show 2s or 7s
- Bally six-digit score display fault fixed by replacing transistor Q14
Source: Pinball Repair help group!! (Facebook group)