For what it is worth here is what I heard from someone off-list: "The OS ROM chip is notorious for going bad in the XEGS. Star Raiders has a flag that bypasses a lot of the OS startup routines and jumps right to the game code, so it is more likely to "try" to work on a failing system. The OS ROM can be directly replaced with an appropriately programmed 27256 type EPROM, but your existing one is most probably soldered directly to the motherboard so will take some effort and care to cleanly desolder it, replace with a socket and EPROM."