So one issue that I was having was that the game would not fire up from a 'cold start'. I would have to turn it off and turn it back on for it to work. I didn't think anything of it when I was fixing up the cabinet itself. My thought was that it reeked of power supply problems because the Nintendo supply used here really isn't the greatest. I've seen this kind of goofballery while working on some Williams WPC System pinball machines, so it was worth a try. But we believe in testing on this site so I hooked up my scope to the game board just to see what was up with it.

So for this exercise, I hooked up C1 to the reset line and C2 to the 5V rail.

You will notice immediately that there is A LOT of noise on the 5V rail. As such, it was screwing up the reset line since it is derived from the 5V rail and a capacitor. After letting it warm up and power cycling, you can see that the noise is still there but is significantly more stable considering the capacitors on the power supply have kind of charged up by this point.

Looking at the power supply schematic, there is almost nothing there. it takes in roughly 10VAC in, rectifies it, then regulates it. Simple enough.

I didn't think that this issue was inherently capacitor related, the older lower voltage Rubycon capacitors have been fairly reliable. I turned my attention to the rectifier at BR1. Testing it in circuit revealed that the diode from one of the AC lines to the positive line was open. So there was our problem. Unfortunately I don't stock rectifiers in that size so instead I decided to retrofit one of the diodes I like using in Williams WPC system pinball machines (since I stock those because it they are an insanely common failure on those). I had a lot of fun bending the leads and whatnot to make it work. This is probably going to be temporary until I order a more proper rectifier for this application.

Original rectifier with heat sink on the left, new rectifier on the right:

Retrofitting the much larger rectifier:

While I had it apart I also recapped the supply. I know it probably wasn't necessary, but I figured "no harm no foul". After testing the power supply I hooked up the boardset. Space Fever is now much happier and is consistently starting as it should. The noise is no longer present in that way and from my testing it seems to be fine.