Thanks all for your answers.
how about trying fluke's warranty as a hail mary
I am not sure but seller is the "original owner". I will ask him. So if he is not original owner not fluke warranty is not applicable i believe.
even having another meter, it depends if you are able to extract an content OR the mcu is locked from being read ....
try the warranty if it is applicable ?
Multimeter seems old so maybe warranty period is over i am not sure. DMM can have GSM bug which may lead warranty replacament i am not sure. I can ask seller for board revision but he may not want to open up device.
It's very unlikely that Fluke left the firmware unprotected from read-back, the trend these days is to lock the end user out as much as possible.
The flash (firmware itself) is should be OK otherwise the multimeter wouldn't be displaying anything that makes sense.
It's possible that the internal EEPROM on the MSP has a hardware fault which would require replacing the MSP of course (and obtaining the firmware to program).
Still most likely to me would be "only" corrupt data in the EEPROM (values that are out of range or data structure makes no sense so firmware throws an error).
Have you tried accessing calibration menu?
I also believe firmware is protected like ST MCU's. I wonder if some known hardware or software vulnerability may MCU have to dump firmware or eeprom data. Some known voltage glitch attack may work also. Since i am not familiar with this type of MCU i am looking for alternatives for dumping fimware.