I'll watch for your progress.
Yes, the 3 pins are for num lock and caps lock (and +5).
The controller is connected to the PCB by a 17 pin "right angle" FFC. This makes it very easy to assemble and disassemble but hard to take a picture of. Here is a picture of the top membrane fitting into a similar 5 pin "strait" FFC that connects the top membrane.
![Custom Buckling Spring Membranes 43587-0](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43588;image)
I wanted to share my method for assembling the key switch layers that solves one of the common problems when assembling a buckling spring keyboard.
The springs on BS switches are a little longer than the frame barrels are deep so that if the barrel frame top is flat against a surface then the springs will not seat properly. My previous solution for this was to use whatever junk i had on hand to wedge around the edge of the frame to prop it up. The problem with this is that a slight bump might knock one of the props loose and some of the springs will unseat.
I start with a box about the size of the keyboard and cut a hole just big enough to fit around the barrels. Pictures show it best. Also showing the assembly steps.
![Custom Buckling Spring Membranes 43589-1](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43590;image)
springs in and nicely seated
![Custom Buckling Spring Membranes 43591-2](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43592;image)
pad
![Custom Buckling Spring Membranes 43593-3](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43594;image)
top membrane with contacts face up
![Custom Buckling Spring Membranes 43595-4](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43596;image)
middle membrane is clear, so it looks the same as the picture above.
bottom membrane (OK, it is a PCB) with contacts face down
![Custom Buckling Spring Membranes 43597-5](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43598;image)
back plate
![Custom Buckling Spring Membranes 43599-6](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43600;image)
nuts on and controller attached. tape keeps LED wires from getting pinched.
![Custom Buckling Spring Membranes 43601-7](https://geekhack.org/index.php?PHPSESSID=d2klm34msj682c04mfm0h0g7rljdl2uh&action=dlattach;topic=40111.0;attach=43602;image)