After work on U15 or U16, check the traces under them
Fine traces run under the U15 and U16 positions and are easily lifted when those chips or sockets are changed. Check each for continuity with a meter (the sockets may have to come out), and use strip socket headers when refitting so the traces stay visible.
Systems
Related tips
- Logic probe states in attract mode: U16 9602 and U15 MC3459
- No clock at the CPU: U15, U16, C14/C15
- Tracing the VMA signal through U19, U14 and U15
- Bally: flipper relay won't fire in game: hairline trace break that still beeps
- MPU board test point voltages
- MPU stops before the 7th LED flash (no 43 V)
- Add a ground jumper on every -17/-35 MPU
- Testing an MPU in the game with only J4 connected
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)