On this page I try to collect all the known issues, possible solutions and workarounds for the uSDX Sandwich

CW: Constant 650Hz Tone can be heard when listening to CW while using headphones and CW Filters

Reason: Low impedance headphones pull current via audio port. This creates ripple on VCC Line, which leads to a feedback loop. Easiest Solution is: Turn down Volume. You can also use e.G. „in ear headphones“ or „active speakers“ with higher impedance. The only true solution is changing C18 (10µF ecectrolytic capacitor) into 470µF electrolytic capacitor. There is enough space between IO Board to fit a THT electrolytic Capacitor lying on the Pins of ATMega.

CW Keyer creates odd timing between Dashes and Dots (in OLED Version)

Reason: OLED needs 100x to 1000x more Traffic (and µC cycles) to write the same information compared to LCD. That´s because OLED writes Pixel for Pixel instead of complete characters. This is using up more µC Power and pulls the rest out of balance. There is no real solution at this moment, only a workaround: Turn off CW Decoder and S-Meter. This prevents unneeded OLED writes.