Unicorn hat stuck rows


I had a look around and couldn’t find anything similar to this issue. I’ve got a unicorn hat, which after a while having anything running with a “high” brightness level gets three of its LED rows stuck into whatever state they are when it happens.
This is a picture illustrating my issue, this happened after less than 1 minute running the random blinky example (https://github.com/pimoroni/unicorn-hat/blob/master/python/examples/random_blinky.py#L7) modified at the highlighted line to a brightness of 0.9.

I’m a new user, so image uploaded to Imgur

I need to power it off for a few seconds before it works again. Has anybody experienced anything similar?

Does it work again if you, and bear with me here because this is bonkers and not generally recommended, remove your Unicorn HAT from the Pi while the software is still running, and place it back on again.

This is not something we’ve seen- even after running a Unicorn HAT non stop for about 72 hours, so I’m going to guess something weird is happening in the software but that’s at best a guess. Knowing if removing and replacing it makes a difference would help- since that means the software is in the same state and still updating it with “stuck” pixel information.

Also, are you running anything associated with sound? Music, etc.

I should clarify that while the program is running (in this example, the random blinky) the other rows work as expected. And then when the program is stopped the three rows stay turned on (even checking that there is no python running on the system).
This happens with all the examples from the repo that I have tried, as long as the brightness is moderately high. Although I cannot draw a definite conclusion, it seems like the higher the brightness the faster the LEDs get stuck.

I have removed and reattached the hat while the program was running with the stuck LEDs and once attached back again the 3 rows of LEDs don’t don anything and stay off. I had nothing else running on the pi, so I would rule out any PWM interference by the audio out.

Well, it seems like yesterday’s test removing the hat has definitely killed those 3 rows of LEDs, I cannot get them to turn on any more :(

That’s even more bizarre- there should be no reason why they’d die. It must be an obscure fault with the Unicorn HAT itself, though, so I suggest you drop us a support email asking for a replacement. Sorry you ended up with apparently dead pixels, hopefully we’ll have you up and running soon!

Thank for you help Phil, I’ll do that.

I realise that this is an old thread now, but I just wanted to point out that I did contact the excellent customer support and got a replacement right away. I had great experience with the pimoroni support and will definitely recommend their products.


You can dig up all the old threads you want if you’re giving us glowing praise :D

Thank you.

I always feel bad shunting people off the forums to our support system, but I’m a disorganised idiot who will forget about your problem unless it goes through the proper channels.