Output voltage on pin 14 (A5) address input pin of SP0256
Your 'SP0256' may be a fake. 

Is that a laser-etched 'Microchip' logo I can see on it? The SP0256 was manufactured by General Instrument (who later became Microchip) back in the 1980's. Nobody was using laser marking back then, so I suspect you have an old chip which has been relabeled. If so then there is no guarantee that it is actually an SP0256, and not something completely different!      

Other telltale signs that it may not be what the label says
are the shiny pins (plated to make them look like new?) and the orientation notch going all the way through (most GI/Microchip DIP packages only had the notch indented into the surface). This is what a real SP0256 should look like:-



28 pin DIP packaging was commonly used for static RAM and ROM chips which had Vss on pin 14 and Vdd on pin 28. You may be able to verify the power and signal pin allocations using a multimeter on 'diode test'. With the positive probe to the supposed 'Vss' pin you should be able to read the protection diode on each signal pin, and you should get a lower reading for the substrate diode from Vss to Vdd. I bet you will find that pin 14 is actually Vss, not an address line!