I have a bad one get out every now and then, if one you got from me is bad I will of course replace it. Just let me know what it is!
See what happens with another EPROM, see if its checksum changes. If it stays the same every time, and this one keeps floating around, there's something wrong with the chip.
The checksum of my chips is always printed on the label, your reader should give the same checksum.
