- 1. The prototype board (NES-ETEPROM-02) was intended for use with EPROMs, whereas my donor (HVC-ETROM-02) was meant for mask ROMs
2. The prototype was meant for NES usage, where mine is a Famicom variant
I may have bitten off more than I can chew on this one, though I'm not discouraged yet.
Here's what I've done so far. I have desoldered the original mask ROMs for PRG and CHR. I have burned new ones and installed them making pin reassignments where necessary. However, at the moment, I believe the MMC5 connection differences are preventing any identifiable behavior from happening. I seem to be getting intermittent behavior from the PPU. Sometimes, when I turn on the Famicom, I'll get a dark green screen, sometimes a lighter green screen, sometimes a gray screen. Occasionally, there will be a cyclical hum sound present.
Upon closer inspection, I'm seeing that the ETEPROM board has CIRAM A10 disconnected, whereas it is connected on the ETROM. When I say it appears disconnected on the prototype board, the photo isn't showing a pin running away from the chip -- if there is a trace going under the MMC5, I wouldn't know.
That was probably too much information to start with, but I'm going to go back and check for continuity between what I see as "disconnected" MMC5 pins, and the places they would be going (to make sure there aren't traces running under my MMC5). I've basically just done an eyeball inspection of the prototype pics and my PCB up until this point.
I'm open to suggestions for a good place to start to try to get this cart booting to something other than a blank screen or a hum. Does it seem like the PRG isn't being accessed correctly to anyone else? I was hoping that even if the CHR ROM wasn't being accessed correctly, that I'd be able to turn it on and hear the game audio. It has no attract mode, just music that plays, which should make it easy to test if that part is working correctly.