This was a repair I was super excited to do. For some background, right now I am in the process of restoring an original Nintendo Radarscope arcade cabinet. The cabinet is in super nice shape but was missing several things.
Anyway, when I got it last night, I excitedly had to wait an hour for the boardset to warm up as it had been sitting outside in the fridged cold. When I first hooked it up, the game did not boot properly, only showing upside down 2s.
The first thing I did to troubleshoot the board was check the sockets. On these earlier nintendo boards, they sometimes used these terrible Texas Instruments tension sockets. They wear out over time and weren't making good contact with the pins after 40 years of service.
Before I replaced them, I pulled each chip, verified the rom to be good using ROMident (an online tool for comparing ROMs to what is in MAME). All ROMs verified good except the CPU ROMs which did not compare with anything online interestingly enough. With the ROMs checked, I sprayed some contact cleaner into the sockets just to see if I could get some more life out of the boards. The game did indeed start working. Problem was that there were graphics issues.
First things first, you may have noticed that the image is slightly shifted to the left. On old Nintendo arcade boards such as Donkey Kong, Mario Bros, Donkey Kong Jr, and this one, Nintendo used two potentiometers on the game board to adjust position. These are always crusty or are broken and I always replace them with new Piher PT15s.
Next step was to start replacing sockets. Since we saw inprovement when I reseated the ROMs on the video board, I decided to start replacing the sockets. Unfortunately, 4 sockets in I ran out. Fortunately though, replacing these sockets fixed the video troubles.
Now I was ready to test it with audio. Fortunately most of the analog sounds were there, but I was missing digital and one of the analog sound effects. On the soundboard I noticed two things: there were some capacitors that had begun leaking and there was some weird Alkaline-like corrosion on the 556 timer. Both of these problems could effect the soundboard's ability to produce the missing sounds.
I ended up putting a socket where the 556 timer was and put a new one in it's place. I also replaced the capacitors that were leaking and ordered capacitors for the rest of the board just to bulletproof it.
After everything was said and done, the game was working and is super cool. I feel like Radarscope is a bit of an underated game, it has nice sound effects and the perspective is unique. It feels like a hybrid between Galaga and Juno First, both really fun games. I can't wait to get the cabinet finished so I can play it for real.
Edited by SNESNESCUBE64