Posting this as it might hopefully help someone else to diagnose and repair their keyboard.
I have a model 01 keyboard marked with the date 2017-02-14. My number 4 key has stopped working and my number 5 key is working intermittently. Before the number 4 key failed it was also working intermittently.
This issue has been developing for about 1 year. I have followed the guide here What to do if your keyboard seems to duplicate keystrokes or a key stops working to clean the offending key switch including opening the switch up and cleaning inside and it has helped most of the time but not as of lately for the number 4 key.
I have bought some spare key switched and replaced the number 4 key switch but that did not help either.
I guess my issue is that I have some break in the lead somewhere. I read this guide and have been trying to diagnose where the fault could be.
top picture: Plugging the keyboard in and using a jumper wire I can not make the keyboard type a number 4 by jumping these 2 points either before or after changing the key switch. But jumping the same points on key 5 and 3 works.
middle picture: I can make the keyboard type a number 4 by connecting the left point with the col4 point.
bottom picture: however, jumping the left point to the D point will not make the keyboard type a number 4, while doing the same on number 3 or number 5 will make the keyboard type 3, or 5.
Having my multimeter set to continuity mode
I can establish that there is a connection between these points.
I got the response from keyboardio support that the issue was probably that the through-hole on the pin next to the D was damaged. The solution was to run a 1N4148 diode between that pin and the col4 test point.
It was easy to find the 1N4148 diode online and they were cheap. After doing the suggested repair the keyboard is back to working normally. I’ve used it for 2 days without any issues. Both the number 4 key and the number 5 key are working without any issues so far.
