found the solution here .. rufus creates the mbr correctly: [URL]
i am struggling to get the dell customized esxi on a bootable usb key.  i tried both 6.5 and the new 6.5u1.   different boot modes bios and uefi.  for transferring the iso to usb, i tried unix dd and mac etcher.   etcher complains that the image is not bootable.  so how do i set the mbr so my r430 will boot from the usb? all i get is "no boot device available ..." any advice would be appreciated.
installing esxi 6.5 from usb