This guide will walk you through the process of transferring the board from the OEM BMW Key Fob to the Miniature Key Fob. NOTE: Take your time, and be patient. Do not force anything. This guide worked for my fob, but I do not claim responsibility for any damage yours incurs while following these steps.
STEP 1: Separating the OEM Fob Halves
Depress the square button on the side of the fob with your fingernail while simultaneously pulling on the key ring loop at the bottom. This will release the physical key from the fob. Remove it and set it aside.
Open the battery compartment cover by unsnapping it from the wide end, tilt it back slightly and then remove it and set it aside.
Use your nail or a small screwdriver to pop the battery out of the housing.
There is a single bolt securing the curved trim piece to the fob. Annoyingly it's a T6H bolt (Torx 6 Security) so you will need to source the requisite bit to remove this one screw. Once you do, you can slide the trim piece off and set it aside.
To remove the trim piece on the other side, hold the fob with the battery side up. Look under the trim piece and you will see some very small gaps (more like narrow slits). Stick a small, flathead screwdriver in there, and then pivot the entire screwdriver up (move the handle up) to flex the trim piece up and off of the plastic clips holding it in place. It should eventually pop off.
This trim piece also holds the buttons in place (they have tabs that sit under that trim piece), so they will likely fall out when you remove it. When you reassemble the fob, have the button side facing up, slide the tabs on the opposite side of the buttons under the fob housing, then snap this trim piece back on over the other side to secure them in place.
Now comes the tricky part. The electronics board is sandwiched between two snapped-together halves of what remains. Separating these isn't difficult, but you'll want to take your time to avoid damaging them. Use a very thin object (I used a tiny flathead screwdriver) to split the two halves along the seam. The easiest spot to start is at the "pointy end" of the fob (left photo below.) Slide the screwdriver into the gap and carefully twist it to separate the halves. Work your way around the fob, continuing to twist it apart until it finally pops into two halves.
Once the board is exposed, use your small screwdriver to gently lift it out of the enclosure. You can set everything else aside, as you will only need the board and the battery, though I recommend reassembling the entire fob without the board once you finish assembling the new fob so that you don't lose any parts.
STEP 2: Assembling the Mini Key Fob
Grab the battery and the bottom half of the new miniature fob. Place the battery into the circular slot in the fob. Make sure it is oriented correctly (flat side down!)
Now grab the board. Orient it so that the buttons are facing up, and the curved corner aligns with the curved corner on the fob case. Note the springs on the back that make contact to the battery. You will want to lay the board down leaving a gap at the bottom, then apply steady pressure on the bottom half of the board to keep the springs compressed while sliding it down and into the housing. Then gently but firmly snap the top edge in. If correctly installed, the board should lay flush with the edge of the enclosure. Take your time. Don't force anything, and don't push too hard on any of the chips/switches soldered to the board. It does fit snug so snapping the top edge in may take a tiny amount of effort, but if you're needing to use 10 tons of force to snap it into place, something is wrong!
Grab the small ring loop that came with your new fob and insert it into the curved slot on the top half of the fob. Note make sure it is fully inserted and sits flush. Be gentle handling the top half of the fob through the following steps to ensure it doesn't fall out until fully assembled.
Now take the top half, and carefully turn it over. Place it over the bottom half, and press the two together. Both ends should partly slip together before hitting resistance from the snaps on each end. Once that happens, push harder on the bottom half to snap the ring end fully down. Then do the same to the front. This WILL take a decent amount of force. If done correctly, the bottom half should sit flush with the top half.
STEP 4: Systems Check!
Test the four buttons to make sure you can feel them click. This ensures something didn't go wrong with the assembly, and that your board is compatible. You should be able to press the buttons, but it shouldn't be OVERLY easy to accidentally press them.
If you ever need to separate the two halves again, carefully slide a thin, wide object (such as a butter knife) into the horizontal gap just underneath the key ring, and then carefully twist back and forth until the two halves snap apart.
Enjoy all that extra space in your pocket!
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