VRC2 and VRC4, conversion

Hi!

I've been playing around with some of my VRC2 and VRC4 boards and I wanted to try to replace the VRC2 chip witch a VRC4 chip on a Jarinko Chie cart.

I burned a set of Kid Dracula translated roms and I rewired the PRG ROM as an UNROM EPROM conversion and the CHR ROM has been unmodified as it's a 32-pin socket. (I've also made a Getsu Fuuma Den repro using this board and I didn't need to rewire the CHR rom at all, it just worked).

I then followed the VRC-pinout to be sure to use the correct setup for VRC4e submapper and the game works....but not all is working. The status section at the bottom is totally corrupted and some of the background graphics are also corrupted.

Is it not possible to convert a VRC2 board to a VRC4 board?
Has anyone tried this before?

Thanks

I'm not entirely certain what you did. Did you leave the VRC2 in place?

The VRC2 is a subset of the VRC4. There is certain functionality(¹) that the VRC2 does not provide, and a VRC4 game that uses that functionality will simply not work.


¹: The VRC4, in its commercial licensed applications, added an IRQ, as well as the ability to control which region of program memory is banked. The VRC4 additionally supported larger amounts of CHR, but only unlicensed games from after the famicom's commercial life used it.

No I swapped the VRC2 for a VRC4

So you used an existing VRC2 board, and transplanted all three major components?

You probably need to just connect the /IRQ line from the VRC4 to the card edge, then.

You were absolutely right, the IRQ was missing, now its working perfectly fine

Thanks!