Three keys dead, how to fix?

[raffas]

I recently assembled my first board in years (hello family commitments!) and it seems three of the switchtes aren't registering.

My troubleshooting this far:

I tested all three switches with a multimeter, and I got a beep from the continuity mode when pressing down the switch. I think that means that the switch is OK, and that the soldering is OK.
I then resoldered each switch to make sure it was fine, continuity tested OK but still no keypress registered
I then unsoldered one switch and tested it, passed the continuity test
I then tested the PCB holes for the switch with the same continuity tester, and nothing. Nothing registered.

[Rob27shred]

Put some pics up of the PCB (front & back) where the offending keys are. Sounds to me like there is either a few missing diodes or a few dead diodes. The only other thing I can think of is the traces going to those switches could be damaged in some way & have been severed Given the switches themselves are fine.

[Esme_Hong]

A lot of keyboard issues end up being a mix of preference and setup, so it’s always worth testing a few different configs before deciding something is a hardware problem. Small tweaks can make a bigger difference than people expect.

[zegonix]

i would check the traces from the controller to the switches, then the diode, then resolder the controller (only when comfortable with soldering surface mounted components).

[xyzzy42]

If one of the pins on the MCU was bad, then all the keys in the column/row of the bad pin wouldn't work.

So you should look up what row, column the three keys are on.  If they are all on the same row or the same column, that's a sign of one of traces or controller being bad.  If any other keys in the problem row/col work, then you know the MCU isn't bad and its pins are soldered fine.  There would be no point in resoldering the controller in this case.

If a trace is broken, what will happen is that every key after the break will stop working.  So a single break could take out the last three keys, and only the last three, in the row/col.  That would be the most likely problem if they are in the same row/col, but other keys (before the break in the trace) in that row/col still work.

If the three keys are in different rows and columns, then it's probably the diodes that are bad (less likely) or not soldered properly (more likely).