Heidenhain DRO fault

[Web Goblin]

If one of the displays is ok I would think your voltage supply would be fine, probably the same supply for both displays and encoders buit you should be able to check this with a decent multimeter. Voltage will be around 5.1Volts.
It could be one of the capacitors on the display board has died or one of the resistors has gone out of tolerance. I get this type of fault on some of our welding equipment displays regularly. Some boards also have an adjustment potentiometer as well for setting up the display and these die as well. It can also be the large driver chip on the board for the led blocks. You could easily swap these around to see if thats the problem or not. You can either attempt swapping out some components for some new ones, the parts wont be expensive, or you would need to get it to someone for repair and calibration.