1: what's the resistor on the cable "manually connect A9 (pin 5) to the unused MMU pin 64."? When you upgrade the RAM from say 1MB to 4MB you need a extra address wire, which is what A9 is. Basically without it, your new chips would be "stuck" with 1MB for example. Thanks for th...

I recently acquired a 520 STFM (IMP chipset, 4 DIL RAM chips, see https://www.exxosforum.co.uk/forum/viewtopic.php?f=56&t=749 ) which I wanted to bring a bit more up to spec. Adding four 256kx4 would've brought it to 1Mb - but replacing the existing four 256kx4 with 1Mx4 would take it to 2MB in...