Fixing a N64 cart that won't save and doesn't have a battery

[+DamonicFury]

I recently picked up a Super Mario 64 cart that played fine, but couldn't save games. Every save slot appeared empty upon boot, and while they would fill up in-game as expected, either a reset or a power-off would wipe them out again.

 

There seems to be a good bit of info out there for fixing carts like Zelda that use a battery for saves, but less so for carts like Mario 64. Here's I how got mine working.

 

1. The part you need to replace is an 8-legged IC labeled BU9850. There doesn't appear to be a good source for these other than harvesting them from a cheap N64 game that uses the same save method... Luckily I had a spare Shadows of the Empire lying around.

 

2. Open up your donor cart. This will require the same gamebit driver needed to open many NES carts.

 

3. Use a desoldering iron to remove the BU9850 chip. Might as well toss the rest of the donor cart in your spare parts drawer.

 

4. Open up the cart with the save issue and desolder its BU9850 as well.

 

5. Solder in the BU9850 from the donor cart. Make sure that it is flush against the pcb,and in the same alignment as the older chip was.

 

6. Reassemble your cart. Should be good to go!

 

Obviously, this only is worth doing if there is some value discrepancy between the two carts. If your problem cart is cheap to begin with, best just to get another one.

 

Of course, I can't guarantee this method will work for you... just that it did for me!

[Atariman]

Did a little digging around as I was curious as to what sort of IC the BU9850 is and saw that it is known to be a 4k serial EEPROM that supposedly is proprietary. It was also discussed that the cartridge is intelligent enough to read the device ID from the EEPROM as well... This got me thinking: If we knew enough about the BU9850, wouldn't it be possible to use a small microcontroller to mimic its functionality? Lots of cheap microcontrollers with 4k+ worh of EEPROM space...

[31336haxx0r]

Maybe it's just a 24Cxx in disguise?

[Atariman]

Maybe it's just a 24Cxx in disguise?

 

Found the thread I was reading earlier:

http://www.assemblergames.com/forums/archive/index.php/t-20908.html

 

Sounds like they felt that the hardware ID was unique to the device. I'm thinking that someone with a scope that can decode I2C/SPI messages could watch the data lines and figure out the ID returned based on that...

[Tr3vor]

Needing to replace a chip of some sort to make the game save again? sounds like a Dallas RTC/cmos/battery chip -.- those things suck, my pentium has one.

 

[TheGameCollector]

If you do this, will the donor cart still work without saving?

[+DamonicFury]

If you do this, will the donor cart still work without saving?

 

I haven't tried it, but I don't see why it wouldn't work if you soldered the bad chip into the donor cart.

[TheGameCollector]

I haven't tried it, but I don't see why it wouldn't work if you soldered the bad chip into the donor cart.

 

Ah see then you can just use a game where the save function doesn't really matter. Maybe a game that only saves the high score (such as Namco Museum 64 if that doesn't uses a battery). Few people would probably find chips for the sports games to be that important either. You could still sell the donor games as long as your listing says "doesn't save".