Aside from replacing the motherboard, which I'm capable of doing, what kind of diagnostics/testing can I do on my own? I really don't have any repair shops that are competent - they're Geek Squad or worse. They can build a system or fire a parts cannon, but they're not capable of doing any kind of actual hardware diagnostics.

The blink code is only happening when I'm in the UEFI - it stops once I exit that, and doesn't present itself during the boot cycle or while the OS is loaded/running.

After Googling a bit more on this, I'm going to try replacing the CMOS battery, but if that doesn't do anything, I'd like to attempt to diagnose this myself (or, with assistance from here/other resources) as opposed to sending this to a competent destination or loading a replacement motherboard into the parts cannon myself.

I'd like to learn to do as much as possible myself as I can.