Folks,

I've been experiencing some interesting behaviour on my Countdown machine recently, and have run into something I cannot seem to troubleshoot.

The score displays went funky, I blew the 2A slo blow fuse for the yellow drop targets at the same time. After the fuse was replaced, the next time the game is powered on the fuse blows again immediately. I traced this to a transistor on that circuit, which has been replaced. The game now functions properly, however the high score seems to have been replaced and the coin count is 55 (typically the coin count maxed out at 15) when I run the diagnostics the scoreboards are blank, except when I run 11 & 12, the scoreboard test, where they function properly. When the game is in attract mode score displays 2 through 4 are missing the last digit. When the game is played in 4 player mode all score displays work properly and the scores appear to be counting correctly as well.

I have recently replaced the driver board with a NOS board. The knocker, as the coil burnt out a while back, and now the transistor on the yellow drop target circuit.

Self diagnostics is clear.

What should I be looking at? Is this a potential CPU board issue?

Thanks in advance.

Appreciate the responses. At this time and after checking into all of the scenarios shared, I'm guessing I've fried something on the CPU board. I'll see if I can trace the issue on the board or replace the board all together.