Broken Pgdn, Z, X, C after desoldering keyswitch


(Anton) #1

I have some problem. When I desoldered the C keyswitch I accidentally pulled it with, how to say… through-hole contact?
And after this PgDn, Z, X, C stopped working.

Do I understand correctly that the contact was connected with a number of layers inside PCB? How can I fix it in this case?
Yes, I’m no good with my hands :slight_smile: Any help would be appreciated.


(Jesse) #2

Ok. What’s happened is that you pulled the copper traces off the board, breaking the electrical connection.

Our circuit boards are only two layers, so all the copper is on the front or the back. It is possible to repair this sort of problem at home with a bit of wire.

If Z,X,C, PgDn stopped working, it’s the ‘row’ wire that broke.

However, it looks like you may have also broken the wire between the ‘C’ keyswitch and the R3C3 diode.

This is the pattern of traces on the front side of the board in that area:

These are the traces on the back:

These are the electrical connections for “row 3” which is PgDn, Z, X, C, V, B:

To repair this, the next step is to figure out whether any -other- connections got broken. Do you have a multimeter handy?


(Anton) #3

Ok, so I got the multimeter and immediately checked “row 3”. It looks healthy between ‘C’ and ‘PgDn’ (But weirdly there is no connection between ‘C’ and ‘V’, which is working).
Trace between R3C3 diode and it ‘naked’ part fugured on photo has connection too.
What and how do I check next? Just in the case I say it again: through-hole contact is fully pulled out itself.


(Jesse) #4

That does make a little bit of sense. The connection between C and V sounds like it got ripped out when the through-hole plating got damaged.

You -can- fix this using thin wire and solder. I’m not finding a good tutorial online, but the rough idea is that you’d use a wire to connect the ROW3 pin on the V key to the ROW3 pin on the C key. Since there’s no longer any metal inside the through-hole, you’d use solder to connect the pin on the key to the wire. Doing this carefully might get you good enough connectivity that you can stop there. But it may be the case that you’d also have to connect the wire to the ROW3 pin on the X key.

To me, it also looks like you’ve nuked the plated through hole on the diode side of the switch. If that’s the case, the repair may be more difficult, since the diode is on the hard-to-access side of the keyboard. If that’s the case, you’re going to need to connect the other (diode-side) pin on the C switch to an 1N4148 diode and connect that to COL2, most easily accessible at the COL2 test point by the 2 key. You -could- skip the diode as a temporary measure. You might get some key ghosting, but it’d let you validate the basic idea pretty easily.


(Anton) #5

Well, now it working! Thank you a lot for helping, Jesse! And of course thanks for this wonderful thing under my fingers right now :slightly_smiling_face:


(Jesse) #6

I’m so happy to hear it. If you’d be up for showing a photo of the repair, it might help somebody else out down the road.


(Anton) #7
  1. I just connected ROW3 pins of the ‘V’ and ‘C’ keys as you suggested - so whole Row3 working.
  2. Next for the ‘C’ key I soldered thin wire to the R3C3 diode, passing him through hole to back side. That is all.