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I have a VN computer with what I assume is a 87c128 eprom. The first memory location appears dead as it always reads as FB, no matter how long I cook it in the eraser, the rest of the buffer shows all FF's. I have a supply of 87c256's. Can I just swap it over and I believe I need to write the bin twice or double it up or something.

Its not 87 its 27c128

Sorry, that's what happens when you start typing before engaging your brain.

Yeah just stack the bins 0000 -3fff 4000 - 7fff

Thanks, I'll give it a go.

Or if your programmer supports it just load it once starting at 4000 - The ECU will never address the 0-3FFF area of the EPROM so its not required unless you want to have switchable maps.