I'm currently trying to convert a full pin SMB2 cartridge to include CHR-RAM instead of CHR-ROM but all I get is garbled graphics.
I'm using a SHARP LH5164D-10L as a CHR-RAM in one game and a NEC D4364C-15L in another.
Here's how I connected them:
Seat the RAM chip 2 pins back (pin 1 of RAM is pin 3 of socket)
cut track to hole 3, 22, 24, 28 and 29
Solder pin 1 to hole 30 (+5V)
Solder pin 20 to hole 31 (CE or CHR /A13)
Solder pin 22 to hole 2 (OE or CHR /RD)
Solder pin 26 to hole 28 (+5V or RESET) <- connected to hole 32 instead since it is 5V
Solder pin 27 to NES pin 56 (CHR /WR), you will probably need to glue in the missing tab on the PC board that goes into the NES, I used a thin piece of metal and super glued it, then sanded it with fine sand paper
What is my mistake? Is there some kind of incompatibilty with those RAM chips or is it the MMC3A that garbles up my game (or would it simply not load if it was the MMC3A's fault)?
Help is appreciated there since I'm kind of getting lost here.
P.S. PRG ROM is soldered like this:
Bend up pins 1, 2, 24, 30 and 31 (or cut tracks 2, 24, 30 and 31)
Solder pin 2 to hole 24 (A16)
Solder pin 24 to GND (OE)
Solder pin 30 to hole 1 (A17)
Solder pin 31 to hole 2 (A18) (N/C on TLROM)