What bad switch diodes do to the matrix
An open diode makes its switch invisible, like a broken wire. A shorted diode lets the strobe leak through, so the switch and others appear at the wrong times. A leaky diode does this only some of the time, which makes it the hardest to find (page 42).
Systems
Related tips
- Bally switch matrix: 5 strobes by 8 returns, numbered 1 to 40
- Switch matrix confused by a bad MPU DIP switch diode
- Clear stuck switches using switch test
- Odd switch problems from corrosion at the DIP switches
- MPU switch connector pins J2 and J3
- Some games add a sixth switch strobe ST5 (switches 41-48)
- Small capacitors across switches lengthen closures
- Prove the MPU switch inputs with the harness unplugged
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)