So I own a logitech g710+ and the bottom and left arrow keys quit working. Also the light on the left arrow key went out. The lights on the number pad also went out, but it still works. I was wondering if there is any way to repair it. I really can’t afford to replace it right now.
Did this happen spontaneously, or did you drop/spill/hit/defenestrate/etc the board? Was there a lightning storm? If a specific event led to this it might be easier to troubleshoot. And these issues all happened at once, yes? In any case…
Maybe a bad solder joint, or a loose board-to-board connector. You could open it up and look for cracked solder blobs, or cold solder points that have disconnected; wiggle around any plugs, especially in the arrow key/numpad block. If nothing is visibly wrong, you’ll need a multimeter to continue troubleshooting.
With the LEDs on, there should be a certain voltage across each LED. The pins that are close together are the LED pins, the other two that are diagonally offset are for the switch. There should be a pulse across the switch pins at probably around 1 kHz to check if the switch is open or closed. I don’t know if a cheap DMM would show this as an AC voltage or not since it wouldn’t be sinusoidal. Start with a known working switch and compare. You can also test the switch with a resistance/continuity test to see if the switch gave out (unlikely).
Once you know what it working and what isn’t, trace the bad voltages upstream. There’s no real information on what each voltage is supposed to be, but you can make educated guesses based on the working half of the board. Generally voltages shouldn’t always be ground when there are more components between it and ground.
That said, it looks like this board is made using small SMD components—notoriously hard to solder. Take care not to lose any parts you desolder, and try not to damage other components near the one you’re working on. Poking around with a meter while powered should be 100% safe, however, since USB is only 5 volts. Just don’t accidentally touch the test leads and short +5V to ground, or cross a probe across the two. Might be better to plug it into a less-valuable computer if you have one while testing.