System failures no WIFI detected.

Hi All,

I've recently had a Mactastrophy . I've a 2.7GHz i7 late 2011, 16GB RAM and two 1TB SSD. Its a great machine worked well always. New battery from Apple 2014. A month ago it just went black screen, couldn't reboot power button wouldn't work. Then after a few hours of fidling it just started up. When I moved it it would go dead, black screen again. I suspected a loose connection so I re-seated all the cables I could. It worked well but when I'd move it with the screen open it would go black. Pressure on the bottom plate seemed to cause the fault. I when to genius bar, no support for 2011. He suggested flex cables. I changed the SSD flex cable rebooted but now no WIFI installed. I've chased this problem for 3 weeks. Changed the airport card, the wifi flex cable. Bluetooth is working. I opted for wifi dongle and upgraded to High Sierra.

But I've noticed slow refreshes on the screen and the machine doesn't operate as before. I suspect logic board.

I was wondering if its worth replacing. The net says reliable logic boards for these machines cannot be found anymore. Also my model is late enough to accept 16GB Ram, a replacement for 2011 may not.

Is it worth fixing? Does it sound like a logic board? Anything else I can try? Can good logic boards be sourced? New Macs are so expensive...any helo will be greatly appreciated. Thank you.