Diodes First, solder the diodes to the PCB. The diodes MUST be attached to the bottom side of the PCB! Not all diodes are directed in the same way, so keep an eye on the arrow markings on the PCB ...

You can exclude the possibility of problems with the PCB, paths and diodes by short circuiting the pins on the ProMicro directly using a bit of wire. Connecting one row pin with one column pin should ...