Replacing an NES PRG ROM with a Flash ROM

PM29F002T-12PC 256KByte flash ROM: http://www.futurlec.com/Memory/29F020pr.shtml

NES 256KByte PRG ROM: http://nesdev.com/NES%20ROM%20Pinouts.txt

Using an Ultima: Quest of the Avatar cart as a donor: http://bootgod.dyndns.org:7777/profile.php?id=105

Pins that don’t match up between the two

WE (pin 31) is active low and should be tied to 5V (*and luckily it already is!)

OE (pin 24) is active low and should be tied to ground

Pin 2 and 22 on the PRG are CE (chip enable). 22 is CE on both chips, and the via for 2 is only connected to 22 so it’s redundant and may be cut.

Things to do:

• Cuts:

• Pull out pin 1 on the IC socket, which will disconnect the NC from A17
• Cut the single trace that leads from via 2 to via 22
• Cut the single trace that is connected to via 24
• Cut the thick trace that connects via 30 to via 31

• Connections:

• Connect via 1 to via 30 (via 1 didn’t have its trace cut, so connecting directly to the via is OK)
• Connect via 2 to trace 24 (not via 24!)
• Connect via 24 to ground (via/pin 16)

Note that the words via and trace are a bit loaded in the above “connection”:

• via: Solder directly to the via (hole) of the pin.
• trace: The trace of this pin has been cut (see above) so when I say trace here I mean that you should solder the connection to the half of the trace that is not connected to the via.

Progress photos

Old PRG ROM has been removed

Traces cut and soldered

It lives! Had to take apart the NES in order to test it, since I haven’t yet cut a hole in the cart. Also had to use a pen to hold down the PCB so it would read correctly :P