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Would it work (and be reliable) if I were to solder a 28 pin IC socket directly onto the legs of an existing board mounted ROM chip, seat a 27C128 EPROM in the socket, and disconnect Vcc (pin 28) from the original ROM chip?

Would this method safely disable the original ROM chip, and give me a reliable working ROM via the top mounted EPROM chip?

I'd rather disconnect the original Chip Enable signal, at pin 20, by wiring that to 5V. This is the well-defined way of putting the IC "to rest".

-- Rolf

Is it OK to simply wire pin 20 directly to Vcc, or does it need to go through a resistor?

Is that all I need to do to make the stacked EPROM work reliably?

Pin 20 can go directly to Vcc. That should do the trick.

-- Rolf

Thanks, Rolf!