EPROM baking

I see the same things. Some chips just won't reprogram. Symptoms include failure to program just like you, but also "chip backwards" errors. Can't remember the chip brands, I just toss them out when that happens. I have not found any way to resuscitate them. Maybe ~10% of the chips I tried had this, so rather frequent, but never any from new old stock. The failed ones were all previously programmed chips, just erased. Marc On Dec 20, 2017, at 6:18 PM, Mark G Thomas via cctalk <cctalk at classiccmp.org> wrote: My stash of TI and NEC 2732s seem to have the disease, but my ST, Mitsubishi, and several others program fine. In the case of a bunch of 2732s, I have tried both a vintage DataI/O 29A programmer and a modern Batronix programmer, with the same results. I don't think I have a programmer problem. I still swear someone in the late 80's had me baking EPROMs in an oven to restore their programability, but I don't remember the specifics. I tried a few at 450F for 15 minutes, but they still won't program. Mark -- Mark G. Thomas (Mark at Misty.com), KC3DRE