TL866 reads a different content every time

[cpt.charlie]

Hi, i have a couple of old PC motherboards that won't post and i think it's a problem related to the bios.

These boards use PLCC32 socketed chips, the chip models are:

Pm39F040-70JC (PMC flash)
W49F002UP12B (Winbond)

I installed the chip in the adapter, selected the right manufacturer/model and clicked read, then i get the content, but if i use the verify function i get many errors 8000-13000, every time a different amount, erase chip is suposed to work but if i check it the chip seems to be intact,  if i try to program the chip, at some point i get a buffer error, my questions are, is this a possible behavior of a damaged flash chip? can i replace the chip with another of the same series and capacity? i have found some chips that even selecting the right configuration the chip ID is read as FF FF does it mean this chip is damaged too?

i'm running the latest software version (6.5) and the latest firmware, the adapter works fine as i can read/program correctly other 39f/49f chips and the programer passes the self test, i've been sucessfull with 25 series chips so i'm confident it's not a problem of my programmer.