How to replace memory card slot on Nikon D40?

Hi Patrick. Before replacing the sd card slot, try bending the pins in the sd card up slightly. It may be more worthwhile and work just as well as replacing the slot. Check out the ifixit guide for the D40 teardown here:

Nikon D40 Mainboard Replacement

Sometimes the pins in an sd card slot get bent down from wear over time. The pins are intentionally bent up toward the middle of the slot so when an sd card is inserted, the pins interfere with the pads on the sd card, creating a pin-on-pad contact. This electrical contact only stays reliable if the pins apply pressure to the pads on the sd card. Once those pins cannot apply a force on the sd card pads, you get sd card read/write errors.

If you are going to teardown your camera, I would take a pair of tweezers or even a toothpick and apply a very tiny amount of pressure to each pin inside the sd slot. Apply pressure to the pin so you are moving the pin upwards toward the inside of the slot.

Be very careful. and in this case, less pressure is better. Those sd card pins are very thin and can break off if you apply too much pressure. In terms of bending them up, only bend them up a few degrees. If you make the pin perpendicular it will no doubt break when an sd card is inserted.

Good luck!