Here's another test you can do to see if the control panel hardware is working. On the back side of the control panel in the center, there's a small hole with a test button. When the panel is blank, use a bent paper clip and push the test button. You should see a white screen with some icons at the bottom. Touch the grid icon, then touch the screen in several locations - you should see dots where you touched the screen. You can also swipe across the screen and you should see a trail of dots. Touch the button at the center to exit this test, and the red x icon to exit the test menu.
If the test menu works, the control panel hardware is working and your blank screen is happening because the printer is not sending an image to display. In this case, a firmware upgrade (described in the previous post) should fix the problem. If the control panel test menu doesn't work and the screen is still blank, you probably need to have the control panel replaced.
I hope this helps,
Alan_R