All lamps in one row are too bright or never light.
A lamp row very bright or dead
Cause: The row's TIP102 is shorted or open; next suspect the row's LM339, then the 74LS74.
Checks
- With the game on, briefly ground the TIP102 tab: if the row lights, the transistor is likely bad; if nothing changes it is likely good.
Fix
- Replace the TIP102, then the LM339 or 74LS74 if needed.
Systems
Related tips
- A row or column of lamps stuck on and too bright
- How the WPC lamp matrix works
- How the WPC lamp matrix is switched
- WPC lamp matrix and GI driver parts
- Where the WPC coil and lamp drivers sit
- How a WPC coil, flasher or lamp driver chain works
- Which transistor drives which WPC solenoid and lamp circuits
- A coil or flasher energizes as soon as the game is turned on
Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)