First, what is the disk image on the uSD card you are using? Is it correctly assigned to drive 0?
What do the onboard LEDs show? Any activity? Red will be on during INIT, green during disk commands, yellow during uSD file access.
I assume you have the USB cable connected to a computer and the serial monitor being displayed in a terminal program. What does it display?
It would be nice to capture the terminal log and post it here.
For reference, I have both PDP11 and PDP8 monitor and console sample logs here:
DEC PDP-11/PDP-8 RX02 drive emulator. Contribute to AK6DN/rx02_emulator development by creating an account on GitHub.
github.com