Boot the board on a non-conductive surface.

Yes, you can verify the soldered RAM works without snapping the whole laptop back together.

Get the motherboard out, place it on a cardboard box or a wooden table (not the anti-static bag – that’s conductive on the outside). Hook up the DC power jack, plug in a known-good display (if possible, use the laptop’s own screen but leave the bezel off, or an external monitor), and connect a keyboard. Then press the power button.

Listen for beeps, watch for the logo, and check if it posts. That’s it. If it boots to BIOS or starts loading an OS, the RAM is fine.

Just be careful: no loose screws touching the board, no metal surfaces underneath, and don’t let the heat sink dangle. If it posts, you’re good to reassemble.

You didn’t come this far to skip the final test and find out later it doesn’t work.