Wednesday, January 15, 2014

Super Metroid SNES Cart Battery Swap (2014)

A short while ago, a great friend of mine purchased a used Super Metroid SNES cart.  However, he quickly realized the SRAM battery was shot, which meant the cartridge could no longer save his game.  I offered to see if I could swap the battery for a new one and give back the cart is functionality.

The first obstacle, I knew, would be the darn tamperproof gamebit heads used by Nintendo to keep their cartridges shut.  I had a piece of scrap aluminum around, and on the second attempt managed to file a passable makeshift gamebit driver.  (For my first attempt, I made the miniature spokes were too thin; because aluminum is so soft, the tool quickly bent out of shape.)

Makeshift hand-filed gamebit driver.
Fortunately, the cartridge screws are only very lightly tightened, and my improvised tool made short work of them.

One down.
One screw out of the cartridge.
Unfortunately, the tool lightly scratched one of the screwholes.
Then came time to have a look at the goodies!

Freshly-opened cart.
The culprit, a dead CR2032.
Look at that battery.  As Shijima said in Ninja Scroll: a strange technique!
The CR2032 is held in place using a manufacturing technique I'd never seen before.  After some research, I realized that you can purchase so-called tabbed CR2032 batteries which come with such tabs preassembled.  The tabs look like they're cold-welded to the battery casing in two spots; I presume this is done before the battery itself is even assembled, because it looks as though the welds on the bottom were made from within the battery.  The spots form a tight bond between the battery casing and the tabs, and it took quite some effort to separate them.

At this point, seeing as how it looked as though I would have to irreversibly deform the tabs when removing the battery, I decided to turn to the internets to see what others thought the best repair method was.  I found a few blogs pointing to the following page:

I thought: tape is an obvious solution, but surely a permanent battery holder would be a much better one!  And I happened to have one lying around from a discarded PC.  I removed the old battery and tabs, and tried the battery holder for fit.

Removed tabs.
Trying the CR2032 battery for fit.
Unfortunately, though it was elegant, this was not meant to work.  I quickly discovered there is not enough space inside the cartridge case:
FAIL!  Not enough space inside the cart.
Luckily I hadn't soldered the holder in place yet.  I simply removed it, soldered the tabs back in and taped the battery as suggested.  The new battery holds quite fast, and I preloaded the tabs with tension so the battery mostly holds in place even without the tape.

Tabs back in.
Battery in place.
I then closed everything up and tested the fix.  Victory!
Closing up the case.  (The soldering job looks terrible in this picture; it doesn't look nearly as bad in real life.)
Testing out the fixed cart with my furry assistant.
The galaxy is at peace!
Edit: seems there was possibly more to this cart's problems than the battery, since it just suffered another saved game reset.  To be continued...

Second edit: many thanks to reader Kincl, who pointed out that Super Metroid is apparently an ornery cart whose SRAM/battery circuit is difficult to restore to health!  It appears this is a somewhat common case:

For what it's worth, this specific cart has held up for just about a week now.  Time will tell how durable the repair ultimately was.

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