Problem booting with K4200 & dual 4K Samsung U28E850R monitors

We have engineering workstations that we just upgraded with dual 4K Samsung U28850R monitors. They works great, once the system is booted, but we are having problems getting past BIOS on a regular basis. Typical voodoo magic required is something like: Power monitors off, boot system, wait 10 minutes, power monitor on, login to Windows. If the monitors are on, we never seen a BIOS message and the system just hangs.

Unfortunately, the “voodoo” works about 1/2 the time, often requiring several retries.

Both monitors are connected via DLP (technically one mini-dlp cable, one full dlp cable - mostly because we had those available). If I replace one of the monitors with a standard definition one, everything boots just fine 100% of the time.

I have a half-dozen of these setups, all behave the same.


Interesting news: The problem only occurs when using a mini-display port cable. If a full cable is used, things work as expected.