Could one bad ground knock out the whole set-up?
It could if you have all of the button and potentiometer grounds connected to one ground pin on the U-HID.
With power off:
- Set your multimeter to continuity/Ohms.
- Connect the black lead to the outer shell of the U-HID's USB connector. (ground)
- Touch the red lead to each tab on the buttons and each outer lead on the pots.
-- You should get continuity (<2 Ohms) on one tab of each button and one of the outer leads on each pot.
-- If you don't get continuity on any of those, you have a broken ground wire. Look for the daisy-chained ground wire and trace it back toward the U-HID.
Scott