Hello,
First of all, sorry for language problems, English isn’t my native one.
We assembled the K8400, along with a second printhead.
At first startup, everything works fine. X, Y and Z axis move perfectly. First filament loads fine. (very happy at this time) 
Then we want to load the second filament. During this process, feeder doesn’t work. So we check the manual again. We found our mistake: we placed the driver board for feeder motor in wrong direction 
After rotating the driver board and checking everything else, we try again, no result. So we switch the driver boards of the two feeders (since we know the first one worked). At power on we get a short on the driver board of feeder 2. 
After this the printer LCD lights up but stays blank when power on.
Today we received some new driver boards and mounted them. But LCD stays blank. We can’t seem to find anything else wrong. What could it be and what should we do?
Any help is greatly appreciated!
