On my '78 Gottlieb Solar Ride, when all five drop targets are down, they move as if they are going to reset but then they all drop again...this happens both when I hit the outhole with 'reset targets'  lit and at the start of the next ball. If 1,2,3 or 4 targets are down, they all rest properly every time. It's got a new power supply and CPU board fitted so hopefully it's a switch or something simple but all the switches appear clean and properly adjusted. Anyone with a Gottlieb System 1 had this problem?

I had the same exact problem on my Solar Ride.
The target bank had a different coil on it to what the manual specifies so I thought it was that but in the end all I had to do was polish the plunger and clean the sleeve.
I think that with 5 targets to reset the target bank coil is on the brink and a small amount of drag is all that is needed to stop it resetting.
Mine has been going strong for over 12 months now so problem solved.