A friend of mine has a RCT that's been rebooting randomly. Sometimes he'll turn it on and it will reboot 4 or 5 times. Other times you can play 8 - 10 games before it reboots. There doesn't seem to be any rhyme or reason.
I'm finding a lot of threads with reboot issues related to Williams machines, but nothing relating to Stern. His brother in law has been repairing circuit boards for decades so he has that benefit, but I was hoping to give him a starting point.