nesdev.com

So strange: I have a modded AV Famicom and a Disk System attached. For some disks, like SMB 2 , the colors always appear correct.

But for some disks, the colors are often incorrect. And if I press the Reset button, the game loads again, but with different colors than the last time. Check out the screenshots of Bubble Bobble below.

What's going on here? Is the problem in the disks (which sounds correct, since some games consistently work as expected)? Or could it be something in the Disk System? Or the RAM adaptor (HVC-023)?

Oh--cartridges generally the correct colors in the Famicom consistently as well.

Screenshots here: http://imgur.com/a/NCixW

Which Famicom games did you test?

Since SMB2 seems to work properly and displays the correct colors all the time my following guesses are:

- Famicom not modded properly
- 2KB VRAM IC damaged inside Famicom
- Faulty Disks of Metroid/Bubble Bobble

Thanks Ice Man.

I tested dozens of carts and the following disks:
SMB 2
Bubble Bobble
Castlevania
Metroid

All exhibit color problem except SMB 2.




So you think all of these things are more likely than a bad RAM adaptor from FDS to Famicom? I don't know much about the hardware (which is why I'm asking this informed forum) but given that carts play perfectly, I was thinking it was something more specific to the disks.

Any suggestions on what to try next?

Hmm, I don't know much about the FDS RAM Adapter itself but perhaps it could be a problem as well.
Cleaned the contacts carefully with a Q-Tip and some isopropyl alcohol?

Maybe the SRAM inside that RAM adapter is faulty. Since they're not that expensive try to get another one first?
Unless someone knows the exact problem I'm only putting up guesses.

Just gave the RAM adaptor a thorough clean with a fiberglass brush and then some rubbing alcohol.

Same bad colors as before...

Any other ideas before I buy a new RAM adaptor?

I assume it's either the SRAM inside the RAM adapter or inside your Famicom or the disks are damaged.

If you can solder, desolder the SRAM inside the RAM adapter and replace it with another one.

Could you perhaps write a RAM test program before trying replacements?

The FDS's CHR-RAM is SRAM, but the PRG-RAM is DRAM. You certainly should be able to replace the one or four DRAMs with a single 32 KiB SRAM, but it's not a trivial drop-in replacement.

Oh, I honestly didn't see those at all (assumed they were logic ICs by the size and didn't read).

But can't one just replace those as well assuming you don't want to use one single 32KiB SRAM? I still see enough MN4264 DRAM on eBay.

I suspect something is wrong with your NESRGB or NES HDMI kit, if you are using one. Your third screenshot shows the Taito logo checkerboarded in a way that strongly resembles NTSC subcarrier checkerboarding. Some bubbles in that screenshot are showing the same effect. I don't know what would make the FDS momentarily disable your kit.

It looks like your palette is set to the 2C03-type paletted. Does this happen on another palette? If so, you may want to inspect the wiring for your palette switch.

If you're actually using a 2C03 or other RGB PPU, please ignore everything I just wrote.

Thanks all. The Famicom has a Hi-def NES mod. And I've tried the other color palettes (via the Hi-def NES on-screen menu). Changes the "tone" of the colors but doesn't fix the issue.

In case this is helpful: Here's a video of the FDS loading view, with no disk loaded. Whereas most disk games' colors are "resetting" every time a new level is loaded (like on Bubble Bobble or Castlevania), the FDS loading view shows the colors constantly changing.

https://www.youtube.com/watch?v=PDjaH3KnaE0

Also worth noting, here's a video from before the Hi-def NES mod. You can see that colors were fine (though picture quality over RF was horrible): https://www.youtube.com/watch?v=XQ5skpll3K4

Does this make anyone think something else could be going on? Someone else suggested to me:

An update:

I seem to be experiencing this with a cart as well, for the first time. (Until now, had only seen this with Disk System games.)

Check out this video of Zelda: https://youtu.be/6q-FNj8c7WQ

Just like most of my FDS games, colors load at certain "key moments" in the game--usually when loading a new level, etc. And then stay loaded incorrectly (or correctly, occasionally) until the next "load".

With every other cart in my collection, colors load correctly the first time I turn the console on, and stay loaded correctly. With Zelda, however, colors seem to be loaded as frequently as entering and exiting caves. And when they're loaded, they have a chance of being loaded incorrectly, as shown in the video.

Any other suggestions? Does this continue to look like an issue with the Hi-Def NES mod to people?

The hi-def NES intercepts the palette writes. It seems that perhaps somehow these writes are not being properly intercepted.
Hard to tell exactly what could be wrong (perhaps a broken mux) without a schematic of the hi-def NES or something like that though.