Raspberry pi400 - uning HATs

hi i have recently acquired a raspberry pi400, have ppurchased an extender cable for the gpio, but can’t get my DOT3K to work on it. are they not supported by the 400?
i went through all the setup process and tried the examples, joystick, needed to change one part of the cd line though to include dot3k as the target. all bargraph leds and screen backlight lights are on at what appears to be the lowest setting but will do nothing else.

I think the Pi 400 should support all HATs, are you absolutely certain you’ve got the ribbon cable the right way around? Which one are you using, exactly?

One from the Pi Hut.

Had another go with it this morning and reinstalled everything, dot3k was completely unresponsive-but did get baking hot along the bottom edge where the leds are - even though none were lit??

did get baking hot along the bottom edge where the leds are

That’s a bad sign, and could mean an electrical short. Exactly which way do you have it connected to the cable and the Pi 400? Could you post a picture of it hooked up but not switched on? Errno 121 is the classic “can’t communicate with the device” error and often means something isn’t wired up properly.

You’ll need to be a little careful with DOK3k, as it doesn’t have the full 2x20 header. It should be all the way over the the left of the cable header.

It was definitely all the way to the left. I had the unicorn hat hd on it a few minutes later so the cable and connection are good