Radio display went out

I have exactly the same problem. Still no solution.

This is what I've done so far

1. Measure drained battery voltage: 2.72V
2. Jump-started and charged battery (it's able to start the engine after turn off)
3. The radio turns on (sounds at the speakers) but the display remains off. Both AUDIO fuses are ok.
4. I disconnected the battery and checked for any short or draining current (plug the tester in resistance mode between battery cables, and resulted in open circuit, no draining burdens)
5. Leave battery disconnected and will test it tomorrow, just in case it's the battery not holding a charge.

I'm not an expert but I like to do things myself. What do you recommend to do next?