Tandy 1000 SL 640k upgrade fail

[FUNCLE]

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?

 

[FUNCLE]

OK this is weird! Only other change on this machine was a NEC V30 8086 CPU. I replaced that with the original 8086 and all is working well. Have the 640k and tested with several programs that had crashed before. So, I've managed to solve one mystery while creating a new one!