Joycon rail replaced, still does not physically connect

Secondhand Switch came in unable to recognize right joycon. Swapped rails with another switch: donor Switch works with suspect rail, project switch still does not work with donor rail.

I do not see any noticeable board damage, and Switch is factory reset so I can’t get into any menus because it’s on the screen to attach both joycons.

I had the same Issue yesterday, the switch was reset and after i was not coming out of the menu with showing to connect the two joy cons, so u just changed the slider, first i changed the wrong slider and after i changed the other slider it was working…maybe change both of it and you got confused

I did double check to make sure I switched out the correct side. Holding for use (left) attached to the motherboard on the right side near the battery.

I was hoping for more of a common cap or resistor that fries that I could check. Looks like I might have to just start at the connector and trace forward until I find a short.