A Model 2 VA1.8 Sega Genesis purchased off eBay as non-working presented as non-working. After several days of diagnosis, tracing and research into the system, I finally figured out that the problem was the corroded trace I identified right off the bat.
When started, the Genesis would output video, but only a black screen. No “produced by or under license” screen appeared, which meant that the Genesis wasn’t actually doing anything. When multimetering the board, 5V power seemed to be solid all over.
The corroded RAM trace checked out continuity between the RAM and the cartridge slot, so I guessed that could not have been the problem. I was wrong!
These traces run between the RAM and the cartridge port, but as I was unfamiliar with multi-layer boards at the time, I didn’t realize that they also ran to the Genesis’s sound/video processor, the VDP. Testing for continuity between the RAM pin and the VDP pin it was destined for identified that one trace was broken.
Another thing which threw me off was that the motherboard had clearly been swimming in something corrosive (possibly cat urine) which had eaten the solder off of a few of the board-edge registration marks. Even though these marks don’t do anything, the board having been dipped in something that could eat solder was worth investigating.
To repair the corroded trace, I scraped at the ugliness with a probe of my multimeter until shiny copper was exposed. Then, I clumsily shoved a pre-tinned resistor leg on there and eventually got it to stick.
Boom: it worked.
At this point, I could now get the “produced by or under license” screen, but no games would boot. Sometimes, they would bug out a bit and I would hear static and see a chunk of a sprite. This told me that it was probably the cartridge port, so I set to work making sure all the teeth of the cartridge port were properly tensioned and none were shorting out when a cartridge was not inserted.
After a bit more wrestling, I was finally able to get it to read a cartridge and fully boot.
Now I can enjoy Puyo Puyo 2 on my Frankensteined Genesis!