Quoted from Matty80:Thanks so much for the reply Lynn.
This is the first SS I've worked on with no prior electronics experience so I'm learning as I go so thanks for the help.
Yes when I run the switch matrix test for the "D" roll-over, it did what you said and listed all the switches on A1J7-14 (Inc switch 25 which I can't find listed in the manual). Tested the diode in that circuit on the mpu board and it was showing voltage both ways so I'm guessing that's bad. I also tested a few others for cross reference and there's about 3 doing the same thing while others show voltage only one way. Is it reliable to test diodes in line or do they need to be removed from the circuit for reliable testing? And yes, there is battery damage to the mpu so I may be fighting a losing battle
The nonexistent switch matches exactly with what I was seeing myself; it's a switch that logically can exist, but physically does not. When we had it with Solar Ride, it would walk through the rollovers/drop targets, then a logical switch past that, but is unpopulated in the physical switch matrix.
Go ahead and replace the diodes, and see if that fixes the issue first. You can usually test those in circuit; transistors and capacitors are more the ones that you can't test in circuit without the circuit affecting the readings.
If that doesn't work, replace the 74xx series logic on the board above those connectors. It's OK to use sockets with the replacements. That should fix it, either temporarily (if the battery alkalines weren't neutralized correctly when the battery was removed, which is actually quite likely) or permanently, and might be helpful in testing. And yes, if the alkalines weren't neutralized correctly, you're going to have a losing battle with the switch matrix.
I know TNT Amusements (toddtuckey) was selling an undamaged System 1 MPU for $125 on this site, you can always check with him to see if he's still got it for sale, the boards are pretty much interchangeable across all 16 machines as long as you plug in the ROM chip you have. Otherwise, you can go for a NiWumpf, Pascal Janin, or even a LISY1 if you're into programming your own ruleset.