Is it a bad click wheel or hold switch?

I’ve performed several iPod surgeries over the years, typically replacing batteries or hard drives. In my latest endeavor, I attempted my first logic board replacement. The existing board was fine; I was upgrading from a 6th gen to 7th gen to maximize the capacity of an iFlash Quad board.

I swapped out the logic boards, reconnected everything, and plugged the iPod into my computer. It restored, but the click wheel was unresponsive. Thinking I received a bad board, I reassembled the iPod with the original board, restored via iTunes… and have the same problem. I cannot reset or get into the diagnostic menu because the buttons won’t work. When I plug in a power cord, the iPod powers up and the “lock” icon still appears and disappears on screen as I toggle the hold switch, but the click wheel does nothing.

The possible causes seem to be 1) I have a damaged click wheel (but wouldn’t the buttons on the board still be responsive even if the scrolling feature didn’t work?), 2) I shorted something on each board during assembly and fried the buttons on both logic boards (seems less likely), 3) the hold switch is faulty and is not unlocking the click wheel controls, regardless of whether the lock icon is showing on screen.

Does anyone have any suggestions on how I can narrow down the problem?