I finally got around to working on a Galaga board for AM and I got it up and running and was leaving it on for a 24-hour test when it crapped out showing a error on ROM 39 (which does not exist). This eventually degraded into a state where it did not display any errors at all, and just seem to hang up at the nonvolatile memory test (NVM OK), and started playing random sounds.

After a little Googling and finding a post from Jrok, it seems that this is the point in the test when the sub/slave CPUs are started up, and the self test waits for them to come up.

Reseating the sub/slave CPUs got the game running again, and also indicated a few more sockets that need to be replaced.  I love working on old games!