Upgraded a Tandy SL to 640k and had issues with some programs. So I changed Memory Diagnostics At Startup to "YES" in the EPROM and machine would no longer post. I removed the memory I installed and was able to boot with the original 384k. Have other hardware I had added including a Paradise SVGA card (16 bit and works in 8 bit slot) and a XT-IDE to CF which works quite well. Could this be a bad Memory IC I installed or something else?