Evan, your note solved my problem. I didn't have to go into the source code, but when you mentioned that "an HDMI monitor without sound did not have the issue" I went to the monitor's controls (I'm using an LG 27MP450MQ44B, 1920x1080 at 60Hz) and simply put it in "MUTE" mode. Now the rig boots with signal, waterfall and speaker sound working, and also with proper screen mapping. This is exactly what I needed. However, my fix to get this to work with proper HDMI screen mapping does require a boot with power to the DSI screen disconnected. I had previously installed a SPST toggle switch on the back because I noted this quirk. Perhaps changing the GTK source code would make this unnecessary, but for now it works. I also have to reboot with both the main power switched off first, and also disconnecting the HDMI cable because that somehow supplies some power to the RPi and the digital board. This is easy to do with the HDMI switch that determines whether I'm using the HDMI monitor for the sBitx or the RPi3 that I use to run WSJT-X from my uBitx V6.
Now I'm going to tweak the power output to DRIVE mapping with hw_settings.ini. I need to tweak the power settings on my sBitx V2 as well.
I'm an HFSignals enthusiast, to say the least.
Thanks!
Jack
N6LN
John Terrell, N6LN