Famicom Wars cart works, but...

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the_wizard_666
Posts: 32
Joined: Thu Feb 25, 2021 2:46 pm

Famicom Wars cart works, but...

Post by the_wizard_666 » Tue Apr 06, 2021 10:56 pm

This is pretty frustrating. So a friend asked me for a translated Famicom Wars, which looked to be a simple chip swap. Indeed, I got everything working except for one thing - the saving doesn't work. Seems the last owner attempted (and failed) a battery replacement. No big deal, I swapped the battery out and put a tabbed one in. Yet for whatever reason it just won't hold a save after powering down the console. I tried everything I could think of, from switching to a new battery to touching the solder on every cap, diode, and resistor on the board, as well as on the WRAM chip. I've checked continuities and have no issues that I can find. I've never had this problem in over 100 battery replacements, and I can't imagine it being from the EPROMs because everything works fine otherwise. It just refuses to hold a save. The only thing I can think might be the issue is that there appears to be a missing capacitor when comparing to the two examples on Bootgod's cart database, but then the game would've had issues from day one. Oh, and the original battery tested around 2.6, so it was indeed due for a swap, making it unlikely to have had issues before then. I can't think of anything else that might be relevant to help troubleshoot it, yet I can't shake the feeling like I'm missing something stupidly obvious :lol: Any ideas?

lidnariq
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Location: Seattle

Re: Famicom Wars cart works, but...

Post by lidnariq » Tue Apr 06, 2021 11:13 pm

Save loss is super cranky, depending on all sorts of things that are hard to measure if you even have an oscilloscope, and more-or-less impossible without.

Replace the electrolytics with new ones if you haven't. Adding smaller low-ESR ceramics can help. One of the resistors is in series with the diode from the battery; make sure the voltage across it always stays low (less than 0.5V, ideally in the millivolt range).

It's worth pointing out that MMC4 is the only NES-era ASIC that Nintendo used an explicit battery protection IC with (the difference between FKROM and FJROM)

the_wizard_666
Posts: 32
Joined: Thu Feb 25, 2021 2:46 pm

Re: Famicom Wars cart works, but...

Post by the_wizard_666 » Wed Apr 07, 2021 12:02 am

Yeah, I read that when I was looking for information before asking :P Sadly, Famicom Wars is FJROM, which means it doesn't have that protection. And I'm not taking my Fire Emblem cart apart to give a buddy a copy of Famicom Wars :P

So after redoing everything a second time, I took it back to step one and booted the ROM up again in Famirom, which seems to think the ROM has no SRAM support. This was confirmed by the NES Mapper Reader tool, which also thinks it lacks a battery backup. I tested with both the English and the Japanese ROM and both showed this. I noticed the same thing on another Famicom ROM, AD&D Dragons of Flame, however the English patch showed the battery as being there, so I didn't think much of it. Could this be the problem? For whatever reason, the ROM itself doesn't think there's a battery backup, even though there should be? And is there a way to fix this without downloading the ROM 100 times to find one that works? :P

EDIT: I am really thinking that the missing byte in the header is the likely source of my issues. I downloaded a header editor and did the relevant tinkering (edited the battery backup byte, nothing more), and now it loads with battery backup in both programs. I'll swap chips in the morning and post the results - I have a feeling that was the problem all along :P

lidnariq
Posts: 10423
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Famicom Wars cart works, but...

Post by lidnariq » Wed Apr 07, 2021 12:28 am

The header only affects emulators, not hardware. So if you've got data loss on hardware, it can't be due to a bad header.

the_wizard_666
Posts: 32
Joined: Thu Feb 25, 2021 2:46 pm

Re: Famicom Wars cart works, but...

Post by the_wizard_666 » Wed Apr 07, 2021 12:50 am

Well hell, way to kill that buzz :P I figured it was a long shot, but there's not much that I can figure that would cause this problem, short of a faulty board. Which thinking about it, it's possible. Like I said initially, the board I have is missing a capacitor when compared with Bootgod's DB.

http://bootgod.dyndns.org:7777/image.php?ImageID=4354

The cap in the top right, next to the WRAM, is nonexistent on my board. It's present on both variants in the database. There is no evidence that it was ever in place on my board mind you, but I have no way of knowing whether this board has always had saving issues or not.

I also haven't replaced anything other than the chips on the board, as I'm not really sure whether the supplies I have on hand are the correct ones to use on the board, and would hate to mess it up worse. On hand, I have 22uF caps, .1uF and 100pF ceramic caps, 1K, 10K and 27K ohm resistors, and IN4148 and IN5818 diodes. Not sure what, if anything, should be used to replace anything...my poor eyesight makes for a hard time identifying the small print :P

EDIT: Another possibility may be a faulty WRAM chip. However, I'm not sure if the RAM I have available (6264) would be compatible with the board (looks like 5864, and both of the profiles on the cart DB have 5264). I'm guessing that's not the issue as the save remains when the system is reset, only losing it when the power is turned off. It does seem to be something pertaining to the battery, or at least the traces leading to it.

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

Re: Famicom Wars cart works, but...

Post by lidnariq » Wed Apr 07, 2021 1:25 am

the_wizard_666 wrote:
Wed Apr 07, 2021 12:50 am
I also haven't replaced anything other than the chips on the board, as I'm not really sure whether the supplies I have on hand are the correct ones to use on the board, and would hate to mess it up worse. On hand, I have 22uF caps, .1uF and 100pF ceramic caps
Put a 22uF and a 100nF cap on the RAM. Make sure that the place for a capacitor next to the RAM only supplies the RAM and not any other IC.
EDIT: Another possibility may be a faulty WRAM chip. However, I'm not sure if the RAM I have available (6264) would be compatible with the board (looks like 5864, and both of the profiles on the cart DB have 5264).
They're compatible, but in general you have to make sure if you add battery-backed RAM that it actually supports the very-low power mode that lets it last a decade or more; faster more thirsty RAMs exist too. Hence "measure the voltage across the resistor from the battery". (BootGod doesn't have a photo of a back of an MMC4 cart, so I can't easily see which resistor that is)

the_wizard_666
Posts: 32
Joined: Thu Feb 25, 2021 2:46 pm

Re: Famicom Wars cart works, but...

Post by the_wizard_666 » Wed Apr 07, 2021 1:42 am

Well, it would appear the board was faulty from the get-go. I added in a 22uF cap in the spot where the missing cap should be, and now it holds a save :) I figured it was gonna be something stupidly easy :P Thanks for the help man!

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