Not much happening here right now, I tried various combinations to get the motors running, but to no avail. I tried motors on M1 + M2, M3 + M4, just to make sure it’s not a bad soldering joint. I tried piggybacking both L293 ICs to allow for a higher current. I tried the motors on M1 + M3, to spread the current of the two motors evenly. The result is always the same, more or less. The motors turn for a couple of seconds, then they stop. The ICs are becoming very hot, adding a heat sink doesn’t really help.
From what I gathered by reading through the adafruit support forum my best guess is that the motors need too much current for the ICs to handle. I can’t confirm this right now because the motors are not marked in any way, so I have no idea about their specifications. I ordered a new multimeter, currently I’m waiting for it to arrive. I hope I can do some helpful measuring when it’s here.