I got klippy running on my expendable Monoprice Mini Select V1 and was brave enough to convert my CR-10 v2.
Compiled the firmware, flashed the CR-10 from my Raspberry Pi, got Moonraker to connect, etc. Everything looked great. The screen was a little dim (FIRST RED FLAG) but I could navigate with the front panel knob. I started by testing the fans one by one. The part cooling fan was running much slower than I thought it should at 100% fan (SECOND RED FLAG). The hot end fan wasn't on, and I figured that maybe it wouldn't turn on until I started heating the hot end.
I put in 150C and nothing happened. The runaway temp protection alarm tripped in klippy (RED FLAG). I bumped the hot end fan and it started spinning, again much slower than it should have (RED FLAG).
I looked at my control box cooling fans and they weren't spinning either. They're 12V quiet fans, and my buck converter lights were on, suggesting it was getting power. I did an emergency shut down.
I thought I'd power cycle the CR-10 and see if that helped. When I switched to power it off, it roared to life. Fans started spinning and the screen fully lit.
This entire time, I was powering EVERYTHING on the printer via USB from the Raspberry Pi. I had no idea this was possible. The board was flashed to klipper firmware only being powered by the Pi USB (not sure if that's the way it's supposed to be or not).
Anyways, this was a long story to get to the conclusion, but I thought I'd share my journey in case anyone else finds themselves in a similar situation. I should have started troubleshooting after noticing the part cooling fan wasn't as fast as it should have been. Also, CR-10 screen, MCU, and fans can be powered a little through the USB port.