Scrambled graphics in reproduction

[tito]

Hello, I'm fairly new to making reproductions, but have been successful on my previous attempts. I'm currently working on Mario 3mix and am having an issue with the graphics being scrambled. The game and sound work otherwise.

What's strange is the title screen appears normal for a split second before changing. I've tried to capture this with the images below, although I was only somewhat successful. Does this symptom sound more like a connection issue between the cartridge and NES, or a CHR/wiring issue? I've noticed the game isn't as tight going in as my other games, but I did verify it worked originally (although this was months ago and we know how finicky the 72-pin connector can be). I've also verified connectivity on the CHR, but it's always possible I'm missing something.

Thank you for any help you can provide!

[tito]

I should add that I did thoroughly clean the contacts on the cartridge

[darknezz19]

Donor used, original rom image info, flash chips used?

[tito]

The donor was Shadowgate. The ROM was the PRG1 SMB3. I used an AM27c040 for the PRG and an AM27c020 for the CHR. Both programmed and verified correctly. I did have to write the CHR at a slower speed, as it failed on the first attempt (I erased it and verified it was blank).

[guitarzombie]

In my experience, so far every time something like this happened that didnt make sense, it was because one of the chips was over-erased.

What makes it weird is the chip will burn AND verify, but once in the system it fucks up. Has something to do with the UV light slowing down the speed of the chip i believe. Something of that nature.

[tito]

Thank you very much for the info. I'm going to chalk this up to a bad CHR. When I erased it, I noticed it took a lot longer than expected. I'll have to order more EPROMs before I can test a new CHR, but I'll report back.