Really easy question from an EPROM noob

[mattv]

Really simple question, so simple you will probably laugh.

Can I take an EPROM that already has data on it and overwrite that data with something else?

I want to repair a couple of CPS1 boards that have had a battery failure and for that some of the EPROMS on the board need to be replaced with patched versions. The patched code is available but new EPROMS are very expensive. Is it possible to overwrite the data on the old EPROMS and recycle them? or can you only write to an EPROM the one time?

[DaemonCollector]

Yes, you can rewrite them, but you need to erase them first. I belive you need a UV Lamp.

[tmasman]

yeah... The erasable kind have a "Window" to the inside, if your chips are solid black, they are not erasable...

You need UV light to erase the EPROM.

It's dangerous to be exposed to UV light though, so if you decide to make your own eraser, please be carefull.

I looked into this a while back, but it wasn't feasible to get into that hobby quite yet.

- tmasman

[D_Zoot]

Yup,   EPROMs are erased with UV lamps...   There's a trick to it however,  the amount of time required under the lamp to erase the data without damaging the EPROM is dependent on the lamp and enclosure design (as well as the eprom itself).   So if you build your own, be prepared to do some experimentation.

Do you already have a programmer?

EPROM erasers start at around $50 and go up. 

Honestly, if you only need a couple of eproms burned, and aren't going to be getting into doing alot of them in the future,  you could probably get them done for around $15-$20 including the chips. 

[mattv]

Looks like my good mate at  www.hobbyroms.com will be getting some business soon.