I (finally!) finished assembling my K8200 kit and wanted to share a work-around for a problem that almost made me give up on this printer.
When I connected the printer to my Mac via USB, the COM port showed up and seemed to be working, except that Repetier (and Cura) did not see any responses coming from the printer. Instead, the Print Panel just showed the commands queueing up, and the printer did nothing. I also did not see the firmware version or any other “ok” messages in the console log window.
Suspecting a firmware problem, I re-flashed the controller with the Marlin project code. I tried each of the three versions of the project from the Velleman site, but none of them worked. Finally, I tried putting the same code onto an Arduino Mega board that I had, and found that it also would not acknowledge any commands from Repetier.
On a hunch, I edited the project to drop the baud rate from 250000 down to 115200. This is set near the top of Configuration.h in the Marlin project. Just comment out the 250000 and un-comment the line below it:
// Excerpt from Configuration.h ...
// This determines the communication speed of the printer
//#define BAUDRATE 250000
#define BAUDRATE 115200
I also had to drop the baud rate in Repetier to match. With this change, both boards were able to talk back to the computer and I was able to move on to solving other problems.
Sharing this info in hopes that it may help someone else.
Mac OSX 10.9.5 and Arduino IDE v. 1.6.4.