If the character set was corrupted the entire display would be garbage.
With that said, all of the “standard” minimOSD/MavLinkOSD fimwares are seriously outdated.
A much better option is MWOSD. MWOSD supports minim, micro minim, MavLink, and Aeromax OSDs as well as the OSDs embedded in the flight controllers popular with the FPV racing folks.
MWOSD supports Pixhawk (PX4), APM (MavLink), and FCs running CleanFlight, BetaFlight, and iNav.
Unlike older systems, MWOSD is completely GUI based so there is no need to use Arduino to compile and flash firmware.
One caveat: For FCs using AurduPilot firmware, MWOSD uses MavLink ID numbers. If you leave the aircraft MavLink ID (SYSID_THISMAV) at the default of 1, MWOSD will work just fine. However, if you setup a new OSD on an aircraft that has a MavLink id that is not 1, the OSD will not work. To fix this you need to either change the id of the aircraft to 1, or you can use the GUI to change the target id on the OSD.
I have three aircraft with OSDs running MWOSD with the Pixhawk(PX4) firmware. Two of those aircraft are quads and they have different MavLink IDs. The OSD on the #1 aircraft worked just fine. It took me a little while to figure out why the OSD on the #2 aircraft wouldn’t work…