PP Keyboard - Top Row Actuation

[johnnycontrario]

I'm late to the party on the PinePhone keyboard's top row (number row) actuation issue, but I found 2 solutions to this problem that are simpler than making tiny washer-shaped spacers.



For anyone who has been living under a rock, here are the symptoms:

When pressing a key on the top row of the PinePhone keyboard, the key stroke does not register at the tactile bump. One has to keep pressing the key beyond the tactile bump for the key to register. That last bit of travel is very squishy, and this is the observation that eventually allowed me to understand the root cause of the issue.


The solutions:

1. Add a tiny strip or 2 of tape on the inner face of the key cap on the hinge side.
   (no need for a shim going all the way around).
   
   With a pair of good scissors and some tweezers, this is a very easy and fast solution. On my keyboard, a single strip of masking tape made a huge difference, and adding a second one seemed to make it feel a little better.
   In my mind, the cons are durability and adhesive compatibility. I imagine the strips eventually shifting around or falling out of place.
   
   
    --- or ---
   
   
2. Remove some material from the hinge-side rim of the keycap.
   
   This solution was the most effective and resolves the root cause of the problem with no compromises.
   
   
   
   
   

But why tho?
Here's how I found these solutions.

I started by validating the original solution of shimming the inside depth of the keycap (vertical distance between inner face and outer rim). I measured a keycap from the top row with high precision vernier calipers and compared this measurement with the the lower row keycaps.

I found no difference.

To rule out the membrane switches on the top row, I moved a number row keycap to one of the letter rows and the problem followed the keycap. I also noticed that all of the membrane switches registered key presses perfectly without a keycap present. After doing a lot more measuring and playing with the membrane key behavior, I realized that when pressing a keyswitch down, the surrounding membrane is displaced and needs somewhere to go.

The top row keycap doesn't have enough space under the hinge side of the cap. The displaced membrane binds against the rim, preventing it from traveling all the way down. Because of this, the conductive ring under the membrane can't make it all the way down to the contacts unless you press harder to flatten the displaced rubber.


To illustrate how it's supposed to work, here's what a lower row keycap looks like when depressed.


Here is how my solutions work.

1. Adding a shim so the hinge side of the keycap makes that side not travel as far, creating room for the displaced membrane under the rim. It has a slightly squishy feel, but the key actuates reliably at the tactile bump.
   
   
2. Removing the portion of keycap that interferes with the displaced membrane allows the keycap to travel all the way down as intended.
   I say this solution is no compromises because the modification is completely hidden from view, it solves the root cause of the problem, and they key does not feel squishy at all. It feels absolutely great.
   
   (Pictured is the proof of concept test. The final modification removed a bit more material than you see here.)
   

I hope someone finds this info useful.

Thanks!