Question about RAM compatibility

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

Moderator: Moderators

Post Reply
Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 11:10 am

I believe my NES has a bad RAM chip. Specifically the VRAM. Sprites show up just fine and I can attempt to play the game but the backgrounds are all messed up. Sound works fine. Cleaning and even changing pin connectors doesn't change it. The messed up background graphics are the same pattern/look every time I try. I can't find any broken traces which makes me think VRAM.

Would this be be a compatible replacement? The only difference I think is that the speed of it is way faster at 15ns. https://www.digikey.com/product-detail/ ... ND/2008361

Thanks

User avatar
Bregalad
Posts: 7951
Joined: Fri Nov 12, 2004 2:49 pm
Location: Chexbres, VD, Switzerland

Re: Question about RAM compatibility

Post by Bregalad » Fri Sep 04, 2020 11:16 am

Toth wrote:
Fri Sep 04, 2020 11:10 am
I believe my NES has a bad RAM chip. Specifically the VRAM. Sprites show up just fine and I can attempt to play the game but the backgrounds are all messed up.
Does it show correctly if you use a game which provide its own nametable VRAM such as Gauntlet or Rad Racer II ?
(I'm fairly sure the Power Pak, Everdrive, etc... also provides their own nametable RAM for those games, someone correct me if I'm wrong)
Toth wrote:
Fri Sep 04, 2020 11:10 am
Cleaning and even changing pin connectors doesn't change it.
That doesn't mean anyhting though, front loaders have really awful connectors.
Last edited by Bregalad on Fri Sep 04, 2020 11:17 am, edited 2 times in total.
Useless, lumbering half-wits don't scare us.

lidnariq
Posts: 9659
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Question about RAM compatibility

Post by lidnariq » Fri Sep 04, 2020 11:17 am

Other people have had problems with 15ns RAMs being too fast and storing glitchy values. I don't know how much slower is necessary, unfortunately.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 11:21 am

Bregalad wrote:
Fri Sep 04, 2020 11:16 am
Toth wrote:
Fri Sep 04, 2020 11:10 am
I believe my NES has a bad RAM chip. Specifically the VRAM. Sprites show up just fine and I can attempt to play the game but the backgrounds are all messed up.
Does it show correctly if you use a game which provide its own nametable VRAM such as Gauntlet or Rad Racer II ?
(I'm fairly sure the Power Pak, Everdrive, etc... also provides their own nametable RAM for those games, someone correct me if I'm wrong)
Toth wrote:
Fri Sep 04, 2020 11:10 am
Cleaning and even changing pin connectors doesn't change it.
That doesn't mean anyhting though, front loaders have really awful connectors.
Oh I forgot the Everdrive menu works fine but games played through it are messed up. I also have a Hidefnes installed in this one and the hidefnes menu works fine. The games are messed up regardless if I run through composite or HDMI. I attempted to play Burger Time, Kung Fu and Zelda, though only the title screen for Zelda and that game looks messed up in a slightly different way

I will try Gauntlet when I get home as I have that cart and I'll try Rad Racer II through the Everdrive.

And yeah, I know the connectors are bad but the fact the messed up graphics looked the exact same made me think it probably isn't the connector. Like all the weird characters and symbols that make up the background are in the exact same spots.
Last edited by Toth on Fri Sep 04, 2020 11:28 am, edited 3 times in total.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 11:23 am

lidnariq wrote:
Fri Sep 04, 2020 11:17 am
Other people have had problems with 15ns RAMs being too fast and storing glitchy values. I don't know how much slower is necessary, unfortunately.
Darn, that's what I was wondering. I guess it wouldn't be too expensive to try it. Used stacks of 10 of Hyundai HY6116ALP-10 chips are only $10 + shipping on ebay I guess so I could go that route too. I liked the idea of a new chip though.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 3:56 pm

Looks like Gauntlet is messed up too. Here are some pics of what it looks like. The graphics are messed up the same way for each game whenever they are put in.
Attachments
IMG_20200904_175209.jpg
IMG_20200904_175330.jpg
IMG_20200904_175253.jpg
IMG_20200904_175148.jpg

lidnariq
Posts: 9659
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Question about RAM compatibility

Post by lidnariq » Fri Sep 04, 2020 4:00 pm

... Tengen or Nintendo release of Gauntlet?

The latter doesn't use system VRAM at all... the former uses system VRAM but also uses an extra 2KB on the cart.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 4:12 pm

Doh, Nintendo, gray cartridge.

lidnariq
Posts: 9659
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Question about RAM compatibility

Post by lidnariq » Fri Sep 04, 2020 4:16 pm

On the bright side, that means it's not the VRAM. On the down side, it's a lot less clear what it could be. Sprites appear to work correctly, so it's probably not the 74'373. Might possibly be the 74'04 ? It'd be weird for that to fail, though.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 4:17 pm

Sorry, I was wrong. It is the Tengen cart. I thought they were black. I just ran down and checked and it says Tengen right on the front unless they both say that? It does say Nintendo as well.
Last edited by Toth on Fri Sep 04, 2020 4:35 pm, edited 1 time in total.

lidnariq
Posts: 9659
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Question about RAM compatibility

Post by lidnariq » Fri Sep 04, 2020 4:29 pm

Classic Nintendo shell shape = Nintendo cart. Tengen shells have a bevel at the top. Both use the same sticker.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Fri Sep 04, 2020 8:49 pm

Through a whole bunch of chip swapping with a good NES it would appear to be an issue with the Hidefnes kit, unfortunately. No clue what it could be as it worked fine when I used it last. Oh well, I never actually used it much anyway as I like my CRT gaming currently. I learned a bit about how the RAM works in the NES through this adventure so it was worth it :)

Thanks for the help.

User avatar
Bregalad
Posts: 7951
Joined: Fri Nov 12, 2004 2:49 pm
Location: Chexbres, VD, Switzerland

Re: Question about RAM compatibility

Post by Bregalad » Sat Sep 05, 2020 1:46 am

lidnariq wrote:
Fri Sep 04, 2020 4:00 pm
... Tengen or Nintendo release of Gauntlet?

The latter doesn't use system VRAM at all... the former uses system VRAM but also uses an extra 2KB on the cart.
I'm pretty sure Nintendo release have different boards, some using a Nintendo MMC3 (TR1ROM) while providing all the 4k nametable VRAM on cartridge and others using the Namco chip (DERROM) and having only 2k extra VRAM combined with the 2k in the motherboard, like the original Tengen cart.

Without opening the cart it doesn't seem easily possible to tell which variant you'd have in hand.
Useless, lumbering half-wits don't scare us.

Toth
Posts: 8
Joined: Fri Sep 04, 2020 11:05 am

Re: Question about RAM compatibility

Post by Toth » Sat Sep 12, 2020 1:16 pm

Just a follow up. I decided to remove and disassemble the PPU "interposer" from the hidefnes which is a real PITA. I also got rid of the sockets that the interposer/PPU go into on the board. One of these things solved the issue. If I had to guess, looking at the sockets on the board that I removed, they were probably the issue here. Over time these probably aren't the best to use. Soldering the interposer to the NES is probably the way to go. My systems are stored in a dry environment (I keep it below 50% humidity in the house at all times) so moisture shouldn't have been an issue. They sure look corroded. Now the only thing actually socketed is the PPU into the interposer rather than both the PPU and then the interposer also being socketed.
Attachments
IMG_20200912_150632.jpg
IMG_20200912_150619.jpg
IMG_20200912_150624.jpg

Post Reply