How'd you get that resolution? I don't see it in sys prefs, and I can't get switchresx to install it.
I'm using the 50 firmware on the 39, no blanking.
I used switchresx, which was a nightmare to get to work. if saving a custom resolution doesn't prompt a reboot message or the custom resolutions don't say something like we tried to load but your monitor couldn't take it after reboot, then you may have to delete either the switchresx preferences file or the file that the custom resolution creates in somewhere like s/l/e/Displays/Overrides, with the most recently created/changed directory being what you created. i believe the files are hidden, so toggling hidden visibility is required. may also need to google those file locations, as I don't recall them exactly. but yeah, deleting the prefs and TV resolution override files can finagle it into working. there are a couple other threads on it elsewhere that can be found googling and were helpful.