I have a couple of dozen Atmega644p based measurement system boards that have been in testing use for two months. After the testing period I noticed that two of them were dead. Everything was electrically fine on the "dead" boards, but the Atmega644p chip had mysteriously stopped executing the program. I connected them to my STK500 and found out that they respond fine to chip erase and fuse settings, but when I try to program the flash memory, avrdude stops with an error about invalid device signature. I tried to use the "-F" force flag with avrdude and got this response:
avrdude: stk500v2_command(): unknown status 0x80
avrdude: stk500v2_paged_write: write command failed
avrdude: failed to write flash memory, rc=-1
Something has happened to these two atmegas during the test run period, because they were 100% functional two months ago.
I wonder, could this be hardware damage for example due to static electricity? Can the AVR be damaged physically so that only the flash memory fails?