It won't turn on

Hi,

It all started unexpectedly when the phone started restarting itself every few minutes. After rebooting, I checked the health app and it says everything is fine.

Then it started losing cell connection, it was showing that it was missing signal. I tried to change the mode to manually select a cell carrier, but it wouldn't let me change anything. After I manually restarted it, the connection came up, and everything worked flawlessly for the next few minutes, then the phone lost signal again. In the meantime, I even managed to make a few calls. After another restart, the phone didn't turn on at all.

Because I didn't want to initially open it myself and touch inside, I took it to a Samsung service center where I was told that the connector on the main board was probably broken because when the guy pressed it from behind in a certain spot, the screen was on it trying to boot. I left it for diagnostics as I was advised. But after the diagnosis they offered to replace the main board for the price I bought the whole phone for, and I declined.

After the diagnosis, the phone tries to turn on, but fails to load the android and goes off again, on the second or third try it is dead again.

I opened the phone and removed the main board. Apparently the connector is sturdy and the board is without any visible problems.

I ordered a spare main board from eBay, removed from a working phone and tested, according to the seller. I haven't received it yet, but I'd like to know what happened. This progressive deterioration, without shock or any external impact seems strange to me.

I would like to repair my mainboard if possible as there is inofrmation there which I would like to save.

In the meantime I also bought a spare connector, but apparently the connector has no problems so I didn't attempt to replace it.

Can anyone give any advice? I notice that almost no one here uses and has almost no information on Samsung A series phones.