The best thing you could do is purchase a busted GBA off eBay. You'll want to make sure you have the same pin connector for the LCD (as there are 2 different types: 32 & 40 pin) as the busted one you buy. So make sure to ask the seller if the one you're interested in buying is a 32 or 40 pin model.
When it comes in, swap out the main board and power it up. From that point, you may or may not need to fix more issues. Good luck and I hope you have success in fixing this GBA up.
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