My initial attempt at soldering on the memory expansion went well enough, but was a complete failure in the end. The problem was all of those pre-soldered pads that exist on the mainboard. I was clever enough to desolder many of them (with copper braid + flux) beforehand, but not all of them.

It is necessary to desolder all of the pads (on the main board) that will lie underneath the memory expansion board, as otherwise they will cause a gap between the two boards, preventing good signal connections later on.

Absolutely critical, and just enough fuss to turn an easy installation job into one that requires considerably more care and skill than imagined earlier.

Soldering on the expansion board is dead simple by comparism.

EDIT: So, I had to remove the installed memory board and start over. Fortunately, this proved MUCH easier than it looked. I just used a nice solder-sucker device to desolder all of the through-holes, and the board slipped off with no fuss. What a shocker!

After that, I spent an hour removing all of the solder from all of the pads on the main board that would fall anywhere beneath the expansion board. Except I missed a couple in the top right (photos).. but they didn't matter too much in the end. This rework made a huge difference, as the player then instantly reported 48MB working RAM.

The remaining 16MB is not working yet (well, half of it is..), but you'll have to tour the photo link above to see why..

Cheers