There are other posts on this subject, but nothing that has a definitive answer. Despite the threads being a year or more older, i did post to request further clarification, but have not received a response. So, in hopes that a new post gains more traction, here it goes...
I'm using a Raspberry Pi 2 model B. I've downloaded Ubuntu MATE 18.04.2 beta 1 and burned it to a micro SD card via Win32DiskImager. I have a USB wifi dongle, which means at first boot up, i'm not connected to the network. The monitor is an Acer S200HQL and I'm using an HDMI-to-DVI cable (with the DVI input on the monitor of course). Upon boot, i see the LEDs come on and then the green starts to toggle which usually means there is life--but no video. The monitor says "no signal" and then the blue light goes off (standby mode).
So i hook the RPi up to my TV via an HDMI-to-HDMI connection. When i apply power to the RPi, i see the "rainbow" square (which should be a RPi hardware/firmware thing, not Ubuntu MATE OS). Then I see Ubuntu MATE start to come up and eventually i get to the desktop. I then ran through the configuration steps (connecting to my network, selecting the language, etc.). Lastly, I modify the /boot/config.txt file and uncomment the "hdmi_safe=1" line, save and close the file, view the file with the more command to ensure it was changed, then power the RPi down.
I then once again connect the RPi to the Acer monitor, and boot up. Same LED activity but still no video AND, maybe more importantly, no rainbow square (which is interesting since that should be a hardware/firmware thing). At least now the monitor does NOT say "no signal" and the blue light stays on. But no desktop, just a black screen.
My assumption is that the rest of the settings are incorrect for that monitor. So although the hdmi_safe=1 forces things "on", they are not the right values and the monitor cannot display what is being sent to it.
Using Raspbian, i booted the RPi up on the Acer monitor (it works just fine with Raspbian), and wrote the edid file using the tvservice command. So i have an edid file for that monitor. Also, using the tvservice command, i was able to get the following info for that monitor:
state 0x6 [DVI DMT (83) RGB full 16:9], 1600x900 @ 60.00Hz, progressive
One final thing (not that i think it has any bearing on the solution to this problem)--I do have both the VC1 and MPEG license keys for this RPi.
So my question is, what should i do next to try and get this workstation up and going with Ubuntu MATE? There are probably a few different options, like forcing the use of the edid (though i'm not sure of what to change/add in the config.txt file to do that), or to ssh into the RPi now that i have it connected to my network and change/check things that way. Any suggestions would be helpful.