Works fine in the emulator, but on hardware it glitches.

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

Moderator: Moderators

Post Reply
mjhagen
Posts: 3
Joined: Wed Oct 16, 2019 4:42 am

Works fine in the emulator, but on hardware it glitches.

Post by mjhagen » Sun Nov 10, 2019 5:09 am

Hi all,

I've just written my first NES game using neslib/nesdoug and it works perfectly in multiple simulators. However, it either immediately or with a few seconds starts glitching, as if the memory deteriorates. It looks like my game dies before my eyes. It's really sad.

I've taken some steps to narrow down the issue, all result in the same glitching:

- Multiple different types of EPROMs (27c512, 27256) both cheap Chinese ones and legit Fairchild and ST.
- Two different donor cartridges: Soccer and Lunar Pool (both NES-NROM-256-06).
- I've compiled and burned one of the examples of Doug and this also glitches.
- I've burned a ROM of Soccer downloaded from the Internet and used that on the donor Soccer PCB and this _also_ glitches.

When I put in an original NES game (Double Dragon II), the console works fine.

I have region unlocked the console using this method: https://aaltomies.wordpress.com/2014/12 ... c-chip-leg

I'm using one of those Willem clone naked PCB ROM writers (it says PCB5. OE-2019 on it). Could that be the issue?

The source for the game is here: https://github.com/mjhagen/Monki-Kong it's a few iteration behind, and I've used a very basic version with just the splash screen to test with, but since other games also glitch, I don't think it's my code that is the issue.

Thanks for any help anyone can give me.

Mingo.

User avatar
Memblers
Site Admin
Posts: 3770
Joined: Mon Sep 20, 2004 6:04 am
Location: Indianapolis
Contact:

Re: Works fine in the emulator, but on hardware it glitches.

Post by Memblers » Sun Nov 10, 2019 5:47 am

mjhagen wrote: - I've burned a ROM of Soccer downloaded from the Internet and used that on the donor Soccer PCB and this _also_ glitches.
Yeah, that's not a good sign then. I've used an older Willem EPROM programmer (V3.5 I think?) in the past without any issues. The only catch was I had to set a jumper to set VCC to something 6.5V when programming ST EPROMs (it was specified in the IC datasheet). Otherwise, they would fail during verification. That jumper might not exist (or be needed) on your board, I have no idea.

Is pin 1 of the ROM definitely hooked up to 5V?

You could change the electrolytic cap on the cart. It wouldn't hurt but I doubt it will help, either.

mjhagen
Posts: 3
Joined: Wed Oct 16, 2019 4:42 am

Re: Works fine in the emulator, but on hardware it glitches.

Post by mjhagen » Sun Nov 10, 2019 6:28 am

Thanks for the reply, on the 27256 I’ve checked the pin 1 voltage and that was up to spec (12v according to the data sheet.) I’ve also recapped the cartridges and NES. One possible next step is try it on a friend’s NES.

mjhagen
Posts: 3
Joined: Wed Oct 16, 2019 4:42 am

Re: Works fine in the emulator, but on hardware it glitches.

Post by mjhagen » Fri Nov 22, 2019 5:10 pm

I need someone here to tell me I'm a big dummy...

In my efforts to clean the donor cartridge and prep it for its new life I removed the solder bridge for horizontal mirroring! Bridged it and everything works now!

User avatar
Memblers
Site Admin
Posts: 3770
Joined: Mon Sep 20, 2004 6:04 am
Location: Indianapolis
Contact:

Re: Works fine in the emulator, but on hardware it glitches.

Post by Memblers » Sat Nov 23, 2019 12:22 am

Haha, I've done the exact same thing. Had one cart where the screen would get corrupt, thought I looked over the entire board, and put it away. I picked up a long time later and immediately noticed I never soldered the mirroring jumpers. :roll:

Post Reply