First you'll need to be able to flash tsop56 S29GL128 chips, I sourced the chips from aliexpress but mouser also has them. Then you'll need to order some flex pcbs from osh park, pcbway etc using the attached gerber files.
This repair will require a microscope or a magnifying glass and some soldering skills. Lots of flux helps.
I've had a King of Route 66 naomi 2 cart for a while that I wanted to repair but it had two bad maskroms and there's no equivalent flash chips. The S29GL128N is close but it's 56 pin instead of 48 so this is why we need the adapter flex pcb in between the chip and the board.
I had osh park make me some as they were cheaper than china for a small run. As you can see I've added vias (holes) to the pads you solder to the board, this makes it easier to get a good connection as you can flow the solder through the hole and heat both pads at the same time. The only problem with this is, osh park wasn't able to make the holes that small so they are too big and split the pads. They still work fine though so I still recommend this version. I have added gerbers with with no vias too though to give the extra option.
Next to remove the bad maskroms and replace them with flex pcbs.
Then once that is done solder the preflashed replacement chips on top.
Then do a rom test to confirm every pin is soldered correctly.
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