So, you’ve got a beloved game cart, maybe your original Legend of Zelda or Final Fantasy, and all of the sudden, your childhood save games are gone? Well, I hate to break it to you, but your game is probably pushing 25 years now, and the internal battery has likely called it quits. Sure, you could buy a replacement CR2032 battery off eBay that features the same welded tabs as the original – but god knows who made that battery – and what happens if you have your NES for another 25 years? Wouldn’t it be great to make it EASY to replace the battery in the future? Well, that was my goal – to replace the welded tab CR2032 in the cart with a CR2032 socket that would allow for easy replacements in the future. Before we go on, a bit of a disclaimer:
DISCLAIMER: I am in no way responsible for any damage to your game cartridges or yourself. Soldering irons are incredibly hot, and can give you serious burns. If you are not familiar with soldering, or any of the steps I am about to describe, at least practice them on a dead cell phone or something first. Do not attempt this for the first time on your mint condition Final Fantasy cartridge. Just don’t. Also, if you are doing this preemptively – and you still have valid save games on the cart – YOU WILL LOSE THEM by following this process. This in no way retains the memory of the cartridge – it only makes it viable for future use.
So, a bit of a disclosure. I have yet to find a CR2032 socket that matches the pin spacing on NES carts. The one used in this tutorial, found on Mouser.com here, has the closest pin spacing I can find, but they are still about 1/16″ (1.5mm) too far apart. I have purchased a handful of different sockets, mostly from Digikey, and none of them come as close as this part found on Mouser. But it’s still not perfect. I am not proud of this job. Coming from someone with lots of SMD soldering experience, it took a lot of kludging to get to work, including lots of filing to make the pins fit. I obliterated pads on the PCB, the solder adhesion is pretty poor, and all around the workmanship is crap compared to what I normally do. But hey, it worked.
This is the socket I am going to use, the Keystone Electronics 101 CR2032 battery holder. As you can see in the picture below, it is designed to actually go above other components on a PCB, so it features very tall standoffs and long pins. We will use these long pins to our advantage, and get rid of all the standoffs.
The first thing we need to do to this socket it to get rid of all the extraneous plastic on the bottom. We want this socket to sit flat against the board. I found the easiest way to do this is to just grab the standoffs with pliers and rip them off, and then file down any remaining stub. Once you are done, it should look like this:
Also, we will need to address the positive clip on the top of the socket that holds the battery in place. You can see, in the picture below, that it curves up towards the end. If you leave this in place, you will not be able to close your cartridge back up, so grab some pliers and rip the last 1/8″ off the clip. This will not affect it’s ability to hold the battery in place.
We are now ready to get started on the game cart itself – let’s dive right in. My patient for this experiment is this less than mint copy of The Legend of Zelda:
Start by opening the game up (see my post on Cleaning an NES Cart for gory details on this), and you should be greeted with the following:
Notice that the CR2032 battery is directly welded to the two tabs that attach it to the PCB. This makes it impossible to directly replace (without resorting to crappy contact force and tape to hold it together). First, we have to excise the old battery. Start by taking some small diagonal cutters and clipping the lead on the battery closet to the cartridge edge (note for the future – this is the ground (GND) or negative terminal of the battery):
Once that tab is removed, you can lever up the battery to provide better access to the positive tab on the battery:
Once that tab is also clipped, you should be left with only the remnants of the two tabs still soldered into the board. Heat each side up with your soldering iron (I use a Weller WD-1001 soldering station set to 610 °C with a fairly large tip for a soldering pencil – this is brute force work, not delicate IC packages), and using pliers, pull the tabs completely out.
Once the tabs are removed, we need to clean up the excess solder (Nintendo went a little nuts on my board) – I used a solder sucker to get the majority of it off, then cleaned it up with solder wick. It doesn’t need to be pristine, because we are about to decimate the PCB:
Once the majority of the excess solder is cleaned up, we need to address the issue of pin spacing. The pin spacing on the socket is .807″ and with my micrometer, it appears the cartridge spacing is closer to ~.730″ – giving us a good deal to make up. Now, you could just bend the pins on the socket to make up the difference, but this would be hard to do and still be able to close up the cartridge case. As well, the material the pins are made out of is prone to snap if you bend it too much. So, I decided to go to town on the PCB itself with a micro-file to increase the pin spacing. This completely obliterates part of each pad that you need to solder too, but if you are careful, you can still make decent contact. With this particular socket, you will also find that the GND pin is much wider than the appropriate hole in the PCB; you will have to widen that through hole as you move it towards the edge of the PCB:
Once you have massaged the through holes on the board enough to accept the socket, it’s time to put the socket into place. Using a quality solder (I skipped a flux pen because of how damaged the pads were anyways), go ahead and solder the pins to what remains of the pads on the back side of the PCB. It will take some coaxing and an excess of solder to make this work – but that’s the price we pay here for a good battery socket.
Once the socket is soldered in place, drop a CR2032 into it. and your PCB should look like the below. If it doesn’t, you soldered the socket in the wrong way!
Now, there is only one issue left. If you go to put this back in the cartridge, you will find the new socket interferes with a plastic standoff molded into the front of the cart to help support the PCB. We need to remove this standoff to get the PCB to fit – don’t worry, the battery socket will provide the same support that the standoff did. I found it easiest to clip the standoff with diagonal cutters, and then file down the remnants:
Once the standoff is gone, go ahead and put the cartridge back together (now is a good time to clean the contacts if you haven’t recently). Throw it in your NES and give it a try:
Well, there you have it. One way to replace the battery on your ailing NES cartridge. I will continue to be on the lookout for better options, as this one took a lot of hand fitting and could certainly be done better. I think this is a better option though that wiring a socket into the board and having it hang loose in the cart, or breaking the weld tabs off and sticking a new battery in the old tabs. Would love to hear if people have better solutions!