I know that parallel EPROMs are not the latest hi-tech technology but I have a problem to solve.
I have two equipments which have a 27C512 EPROM. One of them is faulty the other is OK. I found that the problem is the memory.
So, as to replace the memory, I read the dump from the good EPROM using a Genius G540 programmer. The dump was read OK (I guess).
Them, as far as I know, I used a new and blank 27C512 also from the same manufacturer (ST) to program it.
However, the programming failed. I just got a 73h on the 1st position, and the rest full of FFh. The strange is that the 1st position of the original dump is not even a 73h!!!! ^^!
Then, as I don't have (yet) a UV eraser, I tried to erase on the sun... yes I know it could take a couple days/weeks depending on the sun.
But the must strange thing is that after a few hours of sun... I got "zeros" where I had "ones". How can that even be possible? The UVC only changes "zeros" to "ones"... not the vice-versa :/
Do you think that the new EPROM is faulty? When I bought it it was supposed to be new and blank!