Im programming 27C256 and 27C512 on an Enhanced Willem and I have succesfully programmed several of them using this programmer (I know about the voltage drop problems on this kind of programmer) but if you have an UV eraser at hand and you dont have another programmer you can write them and if verify fails just erase it and write it again.
The problem now its that even with twp and twc at max the programmer is sometimes (around 50%) writting 0x10 instead of 0x00, Im testing using a blank verified EPROM (0xFF) and using a buffer filled with 0x00 and the programmer will randomly write 0x10 instead of 0x00.
Does anyone know if this is related to a bad chip or bad soldering? how can I trace it?
Try to select 27256 and 27512 with twp and twc at max. This problem is due to the limited DC current supplying on this programmer. For the better resuilt on EPROM programming, use other willem programmer instead of this Enhanced version.