Game Boy Cart MROM Transplant
Channel: makho
Date: 27/05/2021

AKA How to repair a cartridge with damaged edge contacts.

TL;DW: Any damage to the actual contacts, be it solder, corrosion, or scrapes (sand paper) cannot be cheaply repaired. The cheapest option is usually to just replace the game but failing that, a more expensive game may be repaired with a cheaper game that uses the same PCB. 

RetroRGB has an excellent writeup on the different surface finish options on cartridge based games (not just Game Boy): https://www.retrorgb.com/determining-the-build-quality-of-a-game-cartridge.html

Regarding surface finishes, if the hard gold contacts are damaged by someone's poor attempt to clean (sand paper) or by solder or otherwise by years of neglect, redoing the gold plating is just not feasible for most people. If you do not already have the tools and experience to do this, the cheapest option is to just replace the game. If you do have the tools and are willing to play around, there are DIY options though to replace the PCB. You can use a cheap donor. Shovelware can usually be had for a few dollars and is very useful for repairing more desirable games that have otherwise intact MROM chips. 

For GBA games, determining the correct donor isn't too bad. There are very few different variations of game PCB. You can find a compatible PCB likely by just searching for games that use the same save type (EEPROM, FLASH, SRAM/FRAM, etc). The save chip has to match exactly (cannot substitute 128K eeprom chip for 8k eeprom game). Most emulators have a database for this but you can use the sanni cart reader DB file ("gba.txt") to narrow down potential donors: https://github.com/sanni/cartreader/tree/master/sd

For GBC games, you'll have to search by games with the same mapper (MBC1/3/5, HuC-1/3, no mapper, etc) and by save size and then verify that the game uses the same chip layout for the MROM chip. Most carts use a 32 pin SSOP chip, some use a 40 pin TSOP chip, some use neither. You can use gekkio's hardware db to narrow down potential donors: https://gbhwdb.gekkio.fi/cartridges/

In a few cases, HDR has replacement compatible PCBs that you can order but the surface finish I discuss in the video and RetroRGB discusses in the article above still apply. Hard gold is still much better than ENIG but that may be cost prohibitive. See HDR's github for the replacement PCB source: https://github.com/hdr/nintendopcbs

I used the miniware MHP30 mini hotplate in this video to transplant the chips: http://www.miniware.com.cn/product/mhp30-mini-hot-plate-preheater/
Bringing the temp above 220c destroyed the PCB so probably don't do that if you want to do this. 

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