LFKeyboards SMK-TKL with SMK Cherry MX-mount switches

August 10, 2019

Reviving vintage SMK keyboard switches with a modern PCB and form factor (sketch notes for now).

LFKeyboards SMK-TKL pcb
(optional) usb-c connector board
87 SMK gen 2 Cherry MX mount switches (from Taobao or Aliexpress)
Cooler Master Masterkeys S PBT donor board (equivalent to CM Storm Quickfire Rapid)
Costar stabilizer set with 180-degree wire bends

Disassemble the donor board

Remove caps, disassemble, and desolder switches from Cooler Master board
I use a plastic gift card to work around the outside of the case, disengaging the plastic clips securing the top
Keep track of the case screws, although not all will be reused
The case, plate and caps will be used. The switches and pcb can be set aside.

Assemble plate/switches/pcb and solder

Snip the fixing pins off one SMK switch for F9
Mount the switches in the plate (pins toward the top of the plate ie. the F-row), putting the snipped one in F9
If the plate has non-rectangular cutouts, the switches won’t clip in firmly, but they fit acceptably well
Put the plate+switches face down
Drop the pcb onto the switches and wiggle into place. If it doesn’t want to go down, check for bent switch pins or switches the wrong way around.
Since the switches aren’t clipped firmly into the plate, press down solidly on the pcb until the switches collapse
Press down on the 4 corners of the plate to make sure it’s as far down as it will go
Apply flux, then solder the 4 corner switches
Connect the JST-PH connector. If you’re using the usb-c board, good, if using the Cooler Master mini/micro usb board, you’ll have to move the ground wire from pin 4 to pin 5.
Plug the board in, and test that it works (4 corner keys)
Unplug, remove JST-PH connector, and solder more switches
I went 1 row at a time and tested after each row

Mount the board in the case

Place the pcb+plate assembly in the case to check for fit
One plastic support peg in the case bottom won’t line up with the hole in the SMK pcb, and must be trimmed (bottom left)
The post with screw hole in the top case also has no matching pcb hole and must be trimmed
With this done, the plate+pcb should fit in the case, flush in all four corners
Remove plate+pcb and connect your choice of JST-PH connector
As before, if you’re using the usb-c board, good, if using the Cooler Master mini/micro usb board, you’ll have to move the ground wire from pin 4 to pin 5.
- If using the usb-c board, use the xacto knife to enlarge the original usb cutout in the bottom of the case.
- The usb-c board is a drop-in match for the mini-usb board in my Quickfire Rapid. It didn’t line up with the mount points for the micro-usb connector in my Masterkeys S PBT.
- I used the original micro-usb connector – fitting the usb-c board in its place may be a challenge and require more case modification.
Reassemble and test
Screw down the plate in 2 spots between the F-row and alpha block (where there were screws originally)
Put the case top on, making sure the clips all engage (4 in back, 4 in front?)
Test

Install stabilizers and keycaps

Install the costar stabilizer clips in the plate
Attach the stabilizer stems to the stabilized caps (shifts, enter, backspace, space)
Attach the wire to the keycaps
Set the stabilized keycaps loosely in place and use the small flat-head screwdriver to press the stab wires into the clips on the plate
Press down on the caps to secure them onto the switches
Check that the spacebar actuates smoothly.
- In my case, if I pushed it all the way down, it would stick
- I think the keycap was interfering with the stabilizer wire, preventing it from returning to normal position
- I fixed it by shaving down the inner edge of the front of the spacebar, directly in front of the switch (with xacto knife)
Install the non-stabilized keycaps, and enjoy :)