[Help] Sharp PC4600 keyboard produces dual scancodes

[LupusRex]

Hello!

I've just finished soldering up and programming a Teensy microcontroller wired to the PCB of an old Sharp PC4600 keyboard from the 80's.
Pretty happy with my progress so far, due to this being my first project of this kind, but now that I type, I get dual scancodes from all keys on row 1. All other keys work fine, it's just the ones connected to the pin on row 1 that produces extra scancodes. It seems to bring with it whatever key is in the next column on the same row.

I'm using a Teensy 3.2 microcontroller, and have used Kiibohd to program it: https://github.com/kiibohd/controller/w ... .0-3.1-3.2

I've tried resoldering the connections, made sure there are no shorts by measuring with a multimeter, changed the affected scan codes from e.g. 0x00 to 0x0, but I am at my wits end here.

[LupusRex]

If it's any help, the keyboard is a Mitsumi PCB with hybrid switches.
wiki/Mitsumi_hybrid_switch