Quote from: sequoia on January 18, 2020, 12:38:07 am While restoring an old PC/XT clone, I needed new BIOS (to fix buggy clone bios from 1987 on the computer). Chip seems to now work ok (nice that you can 'continue' if programming ever fails on these UV EPROMs.), I guess only time will tell if using lower than specified Vpp has any effect on longevity of the programming? Btw, anyone run into similar issues with cheap 'TLL866' programmers? I was wondering if mine is just defective unit or do all of these behave the same? and with VPP set to 11.0V programming was successful!. After some experimenting with voltages I noticed dropping VPP to 11.5V allowed programming to proceed about 75% before erroring out. So, I tried changing settings in the (Xgpro v9.16) programing software to: VPP Voltage = 12.50V and VCC Write = 5.5V (no 6.0V option, next closest is 6.5V), but programming failed immediately.

I looked up the datasheet and seems like programming voltage should be 'Vcc = 6.0V and Vpp = 12.5V'. Software seemed to default: VPP Voltage = 12.00V, VDD Write = 5.00V, VCC Verify = 5.00V.

Chip verified as blank ok, but programming kept failing about half way through with 'OverCurrent Protection ! External Short or IC reverse or incorrect package!' error. I compiled latest Super PC/Turbo XT BIOS ( ), and found some old Intel D27128A chips (to replace MBM27128-25 that was on the motherboard), and thought I'd simply program one of these with a TL866II Plus programmer, but that's where the problems started. While restoring an old PC/XT clone, I needed new BIOS (to fix buggy clone bios from 1987 on the computer).

Usb 27c256 eprom programmer