Save RAM hack for NEC handheld consoles

Another update: I discovered 2 of the address lines were flipped somehow. Corrected and reuploaded the Eagle files and gerber files.

I also modified the proto board by swapping the 2 reversed address lines.  I am still not getting it to work at all.

I am going nut!!!  I've checked and rechecked all the pins from the original Tennokoe, rechecked that they all were correct, all connected with SRAM as well.  Games still reports no save support at all.  I've looked at the schematic of TurboGrafx-16, there is no buffer chip or additional parts between cart pins and expansion pins, both sides are wired straight through.

One thing to note though if you are trying this, there is one more thing I forgot to mention.   Tennokoe II has CDD pin on expansion port pulled to ground. They are floating high when there's no device connected to the system.  CDD pin is not present on cart slot and aren't used on TurboExpress or PC Engine GT. You need to find pin 30 of HuC6280 CPU (the chip one closest to cart ribbon cable) and lift it then short it to ground.  The RF shield hole nearby is grounded and would work with a short jumper wire. 

Still no luck on getting this to work.  I've reuploaded some files. Schematics were cleaned up the best I can. PNG of top and bottom layers, Eagle files, and gerber files added.

I got the new board installed and checked, it did not work.  I double checked that the solder is making connection to the board from the cart connector.  (vias will be covered in final version)

When I used BRAM tool, it reported no BRAM.  When I used TurboGrafx-16 CD System 2.0 card to access memory backup, I got corrupted display instead.  When I used PC Engine CD 2.0 card for the same thing, I was able to enter BRAM area to delete and format but the text is corrupted.

I need to find my microscope to verify all the pins on HuC6201 is soldered and not accidentally floating.  The game I selected at random played fine with the board installed so there's no interference.  If those microscope check didn't find any error, I'd need to try a second HuC6201 chip I have to rule out defective chip.

I really wish there were more documentation on HuC6201 beside the pinout, it'd be so much easier to troubleshoot this or clone the chip with FPGA or something similar.