The Unisystem VS provides 2KB of additional memory to the CPU. I took the 2KB chip (LH 5216) I removed from the PPU in the previous step and soldered it under under the other CPU memory (U1) by bending all the pins upwards.

The /CE (Chip enable) pin is not soldered since this memory must be accessible from $6000 to $7FFF. Pin #7 of the 74ls139 present on the NES motherboard happends to be low during this range so I connected it to the additional memory's /CE pin.

Up