I recently picked up a Nintendo Helifire cocktail table and been having a blast bringing it up. There was one main problem though: the original CPU board wasn't working.

With this though, I was able to cheat because I knew it was a problem on the CPU board. Reason being that I had an extra, but I wanted this one working. The first thing I always do when working on a game that isn't booting is check the ROM data. ROM corruption is a very common issue with arcade games due to their use of EPROMs. Unfortunately, these use 2708 EPROMs. Problem is that none of my programmers can really read these due to them being goofball tri-voltage chips. My solution was just to replace all of them with chips that I can program. What I did was make an adapter board that combines a pair of eproms into one. This reduces the chip count and I was able to program my free play mod onto it as a result. It also assisted me in this repair as it garunteed that I had good ROMs.

Testing with the new ROMs, I still was getting no boot. One thing I like to do with games that utilize 4116 tri-voltage DRAMs is to socket them. They are very high failure compared to other RAMs, so having them socketed on my games is nice. One thing I did find is that several of these RAMs were faulty. I decided to replace the entire bank of 8 to ensure the timings were all the same. Trying out the game, it still wasn't booting!

One thing I like doing is checking all the signals coming in and out of the CPU, in this case an 8080. Everything looked fairly normal on the 8080, so I moved to the address buffers since it's an easy thing to check. On Space Fever/Helifire boards they are buffered using 74LS08 AND gate chips. One input is always tied high for each gate, so they just act as a passthrough.

To my suprise, A8 was stuck low despite having a pulsing input.

Input:

Output:

This is a very obvious problem, either the AND gate there was faulty or something in circuit was pulling A8 low. I went ahead and simply replaced the 74LS08. This chip was what was holding the board back. With a new one it now boots as it should.