Why am I having signal or service problems?

Do you have specific information on exactly what's wrong with the motherboard; i.e., which chip or component is defective? How is your microsoldering expertise? For most of us home DIY-ers, board level repair is generally beyond our capabilities, but I don't want to make any assumptions about your skill level, so let us know what your comfort level is and we can go from there.

If you don't feel like this is something you could take on, the next most obvious repair available to you would be to replace the motherboard. It looks like they're running around $100 USD on various sites like eBay and Amazon, and you may be able to get one for around $70 on AliExpress for the EU version. Here's an example that may work, but you'll need to verify against your specific model number to make sure.

Unlocked Original Mainboard for Samsung Galaxy A52 A525F Motherboard with Android System Support Update Full Chips Logic Board

Unfortunately it doesn't look like iFixit has a guide for replacing the motherboard on your phone, but there's a Spanish site that has just what you need. It's written in Spanish, of course, but used with the Chrome browser's translation it is quite usable and well done.

Manuales / Samsung Galaxy A52 / base plate - Nadie Me Llama Gallina