© Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons), Mitsubishi M5L2764K-5377 , CC BY-SA 4.0

After creating a minor tweak to the firmware for #8042 clock (the PCB version, the breadboard version was disassembled years ago) I needed to burn some 2764 EPROMs with my trusty TL866A. Unfortunately some of the EPROMs couldn't be programmed, but others could. The common factor seemed to be the need for 21V Vpp. Usually the C (for CMOS) chips could be programmed.

I had been able to program these in the past so either my TL866A had developed a fault or the open source minipro software for Linux had a bug. I couldn't find any reports about this in the repo, so that would point to the former. Or hardly anybody programs 21V Vpp EPROMs any more so never hit a bug.

I had already written about ancient 2[57]{16,32} EPROMs that require 25V Vpp, and had concluded that I would not be able to use them. So for these 21V Vpp 2764s, I think the most expedient way forward for a lazy cat is not spend time working out whether my programmer or the minipro software is at fault, or even trying the Windows minipro software in a VM, but just bin these chips. (Or if anybody wants them for the cost of postage, PM me.)

Fortunately my designs already cater for using 27C128 or even 27C256 EPROMs in the same 28-pin socket, and I still have a lot of those, probably more than I'll ever be able to use up, as I'm more ancient than the chips. And anyway the non-CMOS versions of the 2764 are more power-hungry.