original 1.x were to be place between controller PCB and the battery bay. I had planned to get a flat cable to connect to the cart connector but the space is narrow. A custom FFC was doable but it's rather pricey for a small run and with no guarantee it'd work, placing a larger order to reduce per cable cost wasn't worth the risk.
I changed and went to have the board mount directly off the cart connector, became version 2.0. With thinner PCB, there was just enough space to make this work. Currently I am on revision 2.1
Since the non-volatile memory chip did not come smaller than 8KB, and the original save support was designed for 2K, I decided to exploit the extra memory by having optional switch added to change the 2K section. The board can have 8K (2 switches) or 32K (4 switches or 1 hexadecimal switch). Or they can be left as is, locked to 2K only.
Version 2.0 didn't work because I made a mistake. The difference between TurboExpress and PC Engine GT is the pin D0 to D7 is flipped, a form of region lock. I ordered the TurboExpress version for my PC Engine GT, the board was basically getting gibberish and couldn't work at all. Oops... I thought about cutting off and hand wiring those 8 lines but it's a bit tricky in the limited space, I opted to wait a couple weeks for new boards instead.
More to follow when my 2.1 arrives, is populated, and tested. I've attached the latest version of PCB and schematic from Eagle if you want to risk your handheld and play with it or clean up my messy schematic. The PCB is likely the final version and will not see any more changes. I changed PCB's via setting to be all covered since I don't need exposed via for testing or bodge wiring. I'll upload standard gerber files later.
Note: about HuC6201 chip made by Sharp for Hudsonsoft/NEC. They are found in Tennokoe Bank II and possibly other save devices. At the time I had found some suppliers that had NOS supply and attempted to contact them about pricing and ordering. 2 replied they are out of stock even though their web sites said they had some. Other suppliers have not responded at all, maybe they don't know English? Someone help me? Tennokoe Bank II is about $30 on eBay and limited in supply. I do not have any other info on this chip other than the pinout or I would have gotten someone to make a clone of it in FPGA.