I tried to hack in the 8 MB of RAM from a 5400 on my 5500. The 5500 should be equipped with all the necessary bits to add this extra RAM... It even has empty solder pads for the DRAM ICs.
So I lifted them off my 5400 and soldered them onto my 5500. The result? A non-booting 5500.
I never bothered to track down the problem. It could have been one of the following: I could have fried the DRAM by using a heat gun to lift it off the 5400, I could have created a solder bridge on the 5500 when installing the DRAM, I could have left a solder gap and not connected a critical line on the 5500, I could have accidentally torched something sensitive with the soldering iron on the 5500 that isn't directly related to the project, or I could just be missing some extra electronicson the board that cause the 5500 to not boot when the DRAM is installed (though I don't think that is likely).
Anyway, it's been a long time, but from my reading of the tech notes, the 5500 ought to be able to address motherboard RAM just like the 5400. What's more, it may even be able to address 64 MB of RAM on the motherboard if you can find DRAM ICs of the right density. I've never been motivated enough to do all the investigation necessary to complete this project, but it would be pretty darn cool to have a 500 MHz 6500/G3 w/ 192 MB of RAM.
Peace,
Drew
