Oh wow, frustrating obviously these guys aren't honouring their warranty.Hi Ponch,
My unit is freezing a lot at the moment and support from Kremer is non existent. I think using different firmware is my only way out as I don't have the password to download new roms on their website. Is your eng custom rom still working well?
I have been using the eng customs rom for a while and it's been pretty stable and added WiFi. Have you checked the wiring that is, the plugs are in no bent pins etc? There are dip switches that sets the screen size aswell may pay to check that aswell.
Upgrade is simple, keep the car on. Plug in the USB, once finished restart the whole thing. The password is 1234 for the Kremer one, just checked it looks like they haven't updated it.
Apologies for what's happened, I haven't had many problems with it.