Our clock is also just showing dashes.
We took the memory card out and put
it back in and nothing changed.
Your doing it wrong. After you take out the SD memory card click on setup, systems, and reset the settings to the factory default. Wait 10 minutes and then put back the SD card into the slot and the system will restart and the clock should work.
I just reset mine using the small button on the top right corner, near the “cd in” label