Intro Schematics The Timer
to make an Eprom eraser (Erasable Programmable Read Only Memory) come
after building an eprom programmer (that you'll find on my web); those Eprom,
infact, are different from EEprom (Elettrically Erasable
Programmable Read Only Memory) because it need UV-ray to be erased;
I've worked with 27C32,27C64,27C128, 27C256, 27C512 but what you'll read here is true for all the eprom of that family.
programming an Eprom it must be erased (all bit must be "1" -
"FF" in Hexadecimal code); infact it is possible only write "0";
as I said, to erase an eprom you need a UV-C ray "C" with a wave lenght of 253,7 nanometer;
pratically we can use a common germicidal neon, not difficult to find.
datasheet you'll find the exact instruction to erase an eprom, but generally you
need about 15-20 minutes at about 2,5 cm from the UV light (for radiation of 15
you can reduce the time putting the eprom closed to the light;
After same erasing you'll find your exact time.
Avoid to take the eprom under the UV ray for long time, that can damage the eprom and remember that erasing after easing, the eprom will slow down the access time (but this is not really a big problem);
Before erasing be shure the "erasing window" is clear, if not use alcool to clear it.
Continue with schematics
73 de iz7ath, Talino