Yep, that's true. This is the reason why head which previously worked (not perfectly but still) now doesn't work - because main board is broken.
This advice convinced me 😁 Not heartwarming but true.
Thanks!
Hello, all!
I've replaced my print head but it turns out that new head was faulty (it wasn't actually brand new head but from other printer which I bought just for this printhead).
So, order of events was following:
I had fully working printer except that BK was blurry
I bought faulty printer...