Using a HDMI to DVI input cable, Pi video is now displayed on my ASUS VB197 19" LCD display monitor and my ViewSonic VP171s. I tried both monitors a year ago and they failed to work. I assume something changed but can't find any details.
I had cause to run a test this week using the monitors believing from past results they wouldn't work. I was thinking of maybe modifying some of the parameters I stumbled across in /boot/config.txt for HDMI to see if that would make a difference.
Now that the monitors are working, I'm thinking did I have a "shower scene" with the monitors, like Bobby Ewing had on the drama series Dallas in the 1980. Bobby characters was killed off because the actor left the show. A year later after a complete season had finished, he comes back (same actor returned) waking up in a shower. The whole past season was written off as a dream.
I'm curious if someone is aware of Pi HDMI changes that would cause monitors that didn't work a year ago, to suddenly work today. Now that I think about it. A year ago I was using Pi 3 and now I'm using Pi3B+. Maybe that is the change. I need to pull out an old Pi and see what is up.