Check the J3 connector for issues. Make sure the pins aren't faulty. If they haven't been repinned, it may be time to do so. Also be sure to clean the edge connectors with a pink rubber eraser to remove any tarnish that may have accumulated.

http://pinwiki.com/wiki/index.php?title=Gottlieb_System_1#Display_Data_Problems

If that doesn't seem to result in any changes, take a closer look at pins in question are J3-9 and J3-11. Those operate the D1 and D9 digits on the score displays.

Test for continuity between the connector and the MPU. Then on the other end, between the displays and their connectors. And finally all together from the display boards to the MPU.

If everyting tests good, then it would be time to start looking at some of the chips on the MPU.

Does the last digit work in the display test?

You will need to reset your high score and it should be fine

Yup, it sounds like you had garbage in the memory.

Ah well, I went straight for the technical troubleshooting first. Yep, garbage values in memory are common and will do odd things. Usually, garbage characters get displayed instead of actual numbers, which tends to be the giveaway for that issue.

I just had the same exact issue come up. Resetting the High Score did the trick. Looking at some of the other audits there were other garbage values in there too. Out with the garbage.

Nice that I could find this post - the issue is clearly stated and defined in the title by the original poster ! Nice job...... and the bonus - a simple solution that I wouldn't have thought of.

Bumping this up for others to see.