Help with project: two keys register when I press a key

[phoible]

I'm assembling an ALPS64 PCB with cream ALPS Switches, and I've noticed that when I press some of the switches, two keys register. Even stranger, this behavior isn't always symmetrical, so that when I push the 'u' key, both 'u' and 'p' register. However, when I push the 'p' key, only that registers. The keys that are registering double are K13 and K61 - K65.

I verified everything after I soldered the diodes, and all seemed to be in order. It's possible that I accidentally fried some diodes when I was soldering in the switches, although I was pretty careful not to touch any diodes or traces with my soldering iron (I clearly screwed up something).

Also verified all of the switches before I installed them, although I have seen switches before that didn't test as bad but then malfunctioned when installed.

Any ideas on what could be going wrong? Happy to provide pictures of the back of my PCB if that's helpful.

[phoible]

Here are the relevant pieces of the PCB.

[Findecanor]

Did you solder the microcontroller on? It looks as if two of its legs are bridged by solder, but I could be wrong.

A broken diode should result in no key press at all.

[Tactile]

I wouldn't mind seeing more solder at the cathode of D53 & D64. And D75. And D06. And D61.

If I were you I'd just re-solder all the diodes. Make 'em all look like D04.

[phoible]

Did you solder the microcontroller on? It looks as if two of its legs are bridged by solder, but I could be wrong.

A broken diode should result in no key press at all.

No. The microcontroller came soldered in. Inspected it with a magnifying glass, and it appears to be correct (it just looks that way in the photo).

[phoible]

I guess the thing I still don't understand is how two keys could be registering (particularly in an asymmetrical way). As Findecanor said, if a diode is broken, there shouldn't be any keypress. The diodes are soldered onto the other side.

Since most of the affected keys are sequential, I wonder whether something could be bridged (it's possible that I didn't cut the diode leads on short enough, and a few of them are making contact with the steel plate). I really don't want to unsolder all of the keyswitches, but maybe that's my best bet...

A broken diode should result in no key press at all.

[phoible]

So I took the whole thing apart, and activating each pad now only presses one key. So I'm guessing that one of the diode leads was making contact with the plate.

Now to reassemble it again...

[phoible]

Finally finished this project.

I lifted a bunch of pads desoldering and resoldering the switches, and ended up having to use a bunch of jumpers to get all of the keys working.

For some reason the solder I'm using is a pain to remove - much harder than the stuff that was used in the AEKII I desoldered (probably because the old stuff is lead-based).

[Joey Quinn]

I'm not sure what solder you're using but I never have any issues with this stuff.

https://www.amazon.com/Kester-Rosin-Core-Solder-Dispense-Pak/dp/B00AYJ0B7Y/ref=pd_sim_469_1?_encoding=UTF8&psc=1&refRID=375V7NEFE1Y6VKPRGCZP

For future reference, using flux will make desoldering way easier.