Garbled sprites on FDS

[Zycrow]

Hello - I'm not sure if this is the correct part of this forum to post this question, but here we go.

A few weeks back I got a Famicom Disk System. It works almost perfectly, but - in some games worse than others - the sprites have garbled, glitchy areas. It's worst in Mario 2, where half of Mario/Luigi is garbled.

I've discussed this issue at length over at Famicom World (here is the thread for the full background), and it was recommended that I try asking about the issue here since it seems like it might be a microchip issue and this is a more technical forum.

I'd appreciate any advice. Please keep in mind that I can be a bit of a tinkerer but I'm no engineer or programmer - I'm kind of a fish out of water here.

[lidnariq]

Most things I can think of that would cause obvious corruption in one place (graphic data) would cause corruption in many (crashes)...

The guesses I have:
- Something's wrong with your disks
- All the games you have just happen to store the graphic data in the same area on disk, and the drive head is tracking poorly causing incorrect data when reading graphics but not program data
- Something's wrong with the FDS adapter's graphics RAM
- Something's wrong with the FDS adapter's BIOS

Unfortunately, without the ability to run arbitrary code on it, I have no idea how to go about debugging which of these things could be wrong. I can't really tell what's going wrong from the picture on your thread at FW... could you provide a picture of Mario (or anything else corrupted) against a solid background?

[Bregalad]

Are the sprites garbled when you switch on the FDS with no disk (the BIOS intro with Mario and Luigi jumping) ?

Does normal Famicom carts works fine ?

[Zycrow]

Unfortunately, without the ability to run arbitrary code on it, I have no idea how to go about debugging which of these things could be wrong. I can't really tell what's going wrong from the picture on your thread at FW... could you provide a picture of Mario (or anything else corrupted) against a solid background?

Affirmative. I'll take some more pics of SMB2 as well as the other disks when I get home tonight.

Are the sprites garbled when you switch on the FDS with no disk (the BIOS intro with Mario and Luigi jumping) ?
Does normal Famicom carts works fine ?

The sprites are not garbled on the BIOS screen; normal Famicom games work perfectly.

[Bregalad]

Then this implies the only problem can be your disk drive or the cable that connects to it. The RAM adaptor can only work perfectly if the intro work perfectly.

However, there is CRC checks on disk loads, and any bad loads should result in a disk error instead of corrupted data being loaded. However, the RAM adapter's character RAM is fine, and I don't see how it's ROM could not be fine considering ROM is one of the most solid component ever by it's "read only" nature.

This is really a strange problem indeed.

[MottZilla]

The problem could be with your RAM adapter. The BIOS doesn't use all of the Character RAM. Maybe there is a problem with an address line on the chip. It could be that a solder joint went bad or the chip somehow is damaged or not working now. I would try another RAM adapter if that is a reasonable option for you.

[Zycrow]

The problem could be with your RAM adapter. The BIOS doesn't use all of the Character RAM. Maybe there is a problem with an address line on the chip. It could be that a solder joint went bad or the chip somehow is damaged or not working now. I would try another RAM adapter if that is a reasonable option for you.

I am considering buying a second RAM adapter to see if that's the problem. I wanted to see if I could rule out other possibilities before actually spending any money, though.

Anyway, here are some more pictures.

The BIOS screen, free of garbling:



Moero TwinBee, which shows the worst garbling of all of my disk games. You can see it in the clouds, the score count, and TwinBee's shots.



It's just barely visible on Pidgit here in Doki Doki Panic. This game has the least issue with garbling.



Here are a couple more shots from SMB2, hopefully it's clearer in these ones. You can see it on the Koopa shell too on the second pic.





It's pretty bad on Baseball, which is on side B of SMB2. You can kinda tell from this pic.



Metroid has it in a few spots. Sometimes Samus' cannon is garbled or part of her sprite disappears, and sometimes little graphical elements pop up around her while she's moving. Not as bad as Mario or TwinBee though.





And finally, here's a pic of the innards of my RAM adapter, just for funsies.

[koitsu]

Zycrow, do you live in the United States? If so, I'd be willing to send you (temporarily) my FDS RAM adapter (which I know works, as does my entire FDS for that matter) to see if replacing that fixes your problem. You would need to send it back to me (on your dime) after confirming/rejecting. Let me know.

[lidnariq]

So, here's the thing that makes this Really Weird:

In SMB (LL), sometimes the right lower half of his body is made of a reflection of the left lower half. Same exact tile. Coming from the exact same place in memory. Which is what seems to on screen in both the original photo you posted and at least the latter of the two you have here. And yet, Mario's right half is distorted, and his left half isn't.

In Moero TwinBee, I haven't even the foggiest idea where that "half bubble" image is coming from: I don't see it in the pattern tables. It's supposed to be a simple 5x5 sprite (padded into an 8x16 cell, hence "half" bubble).

Buh. I have really no idea what could be causing this ... it's definitely not simply the adapter's CHR RAM, if that's even to blame at all. I don't suppose you might have access to another famicom to test on, also ?

[tepples]

In SMB (LL), sometimes the right lower half of his body is made of a reflection of the left lower half. Same exact tile. Coming from the exact same place in memory.

SMB and SMB2 (J) do this to save 3 tiles on the sprite side of the pattern table, 1 for small Mario and 2 for Super Mario, even though it twists Mario's legs into a painful turnout. This was fixed in Doki Doki Panic and SMB3, and the versions of SMB and SMB2 (J) in Super Mario All-Stars use the SMB3 graphics for Mario.

[Pokun]

Since that many games has graphical problems I wouldn't suspect the disks. I suspect the problem lies in either the Famicom or the RAM Adapter (or in the drive head as Lidnariq said). As can be seen in that Famicom World thread, reports of faulty CHR RAM chips in RAM Adapters has appeared before, so I wouldn't rule out that either.

As was said before, it would be best to first try a working RAM Adapter and/or try your RAM Adapter on another Famicom or NES.

[Zycrow]

Well, at the very least I'm learning some things about how the FDS ticks! Seriously though, thanks for everyone's input so far.

Buh. I have really no idea what could be causing this ... it's definitely not simply the adapter's CHR RAM, if that's even to blame at all. I don't suppose you might have access to another famicom to test on, also ?

Unfortunately I don't. I do have another Famicom, but it's definitely not working (pretty sure I fried it by using a NES AC adapter many years ago).

Zycrow, do you live in the United States? If so, I'd be willing to send you (temporarily) my FDS RAM adapter (which I know works, as does my entire FDS for that matter) to see if replacing that fixes your problem. You would need to send it back to me (on your dime) after confirming/rejecting. Let me know.

I do live in the states, and I'm happy to take you up on this offer, so long as you're willing to risk sending your hardware to a stranger!

[koitsu]

Zycrow, do you live in the United States? If so, I'd be willing to send you (temporarily) my FDS RAM adapter (which I know works, as does my entire FDS for that matter) to see if replacing that fixes your problem. You would need to send it back to me (on your dime) after confirming/rejecting. Let me know.

I do live in the states, and I'm happy to take you up on this offer, so long as you're willing to risk sending your hardware to a stranger! :mrgreen:

I do as long as I have your full name, address, and a telephone number for contact in case anything odd comes up, I'm fine with it. I tend to operate on the notion that most people here on nesdev are good-natured and not malevolent.

There's the inverse option too: you could send me your RAM adapter and I could try it out on my FDS + Famicom (both of which are confirmed working). I don't have the same FDS games you do, but I do have Metroid. My FDS collection is limited to Kid Icarus, Metroid, SMB2 (Japanese version), and Falsion. As for trustworthiness, I think pretty much every person here could vouch for me on that.

Either option is fine by me.

The added bonus to the latter choice is that if it does turn out to be your RAM adapter, I might be able to figure out what part is broken in it (maybe some bad RAM inside of it, for example) and try to repair it for you for free (including cost of parts; yeah, I'm nice like that). I'm good with a soldering pencil and "so-so" with a multimetre, and do have access to an oscilloscope if needed, but I'm not good with EE in general, so would probably need help from the amazing number of EE-savvy folks here. This is all optional of course, not mandatory in the least.

Think about it and let me know -- as I said, either option is fine with me.

[Zycrow]

Think about it and let me know -- as I said, either option is fine with me.

Cool! I'll send you a PM and I'll update the thread if more is figured out on this issue. Again, I appreciate everyone's help.

[koitsu]

So I got Zycrow's FDS RAM adapter today...

The issue does not appear to be with the RAM adapter. I tested multiple games (specifically Kid Icarus, Metroid, SMB2, Falsion, and Twinbee) and I see absolutely no graphical corruption of any kind. I tried with two different Famicoms as well (Famicom AV and original Famicom). I also tried gently wiggling the FDS RAM adapter cable while disk I/O was going (thinking maybe bad connection in cable might cause data corruption).

If cartridges don't have this problem, then that would mean the issue is either with the Famicom itself (are there edge connector pins which the FDS uses that cartridges don't? I'm unsure), or with the FDS itself. The latter has my vote, but I suppose it could be the former as well.

I'm betting there is some particular chip inside of his FDS which is busted -- I think we can (mostly) rule out the disk drive itself since CRC errors would get detected, but I am certain there is other circuitry that is used ""past"" that point, i.e. before or during the data is loaded into the RAM adapter, which could be corrupting something.

Random question for Zycrow: are you powering your FDS with an AC adapter or C batteries? I power mine with an official AC adapter (cost me an arm and a leg).

The best I can do in the meantime is:

1. Clean all the contacts on his FDS RAM adapter (no harm in doing that, unless already done),
2. Return his FDS RAM adapter to him,
3. Also send him my FDS + FDS RAM adapter so he can use that to troubleshoot which exact piece of hardware is busted, then send me my stuff back once he's narrowed it down.

Repairing FDS systems is not something I'm good at. Yes I've opened one up to try and repair a drive belt (I failed), but I always hate working on those things given all the sensitive parts and how timing-oriented the dang thing is; the last bad FDS I had (bad belt / bad motor / timing / something, even after FDS belt replacement) I gave to Matt Conte because I couldn't be bothered to try and fix it.

If other folks here have ideas of things to try, I'd be happy to give them a shot.