I sought support from the local authorised distributor who sold me the unit last year – he responded that he no longer sold it, and being 2 months out of warranty would not provide any assistance.
I’ve lodged a support ticket, but haven’t heard anything yet.
So I’m realising that while I paid over $400 for this unit and expansion board, when it blows up, I’m on my own. And where I live we’re currently in a drought, and every day the controller lies dead, everything is drying out as we head towards summer.
So I unhooked the unit and took it to the bench. Probing the I2C lines showed they were both sitting low (~0.5v), which would explain why the real time clock wasn’t working, nor would any valves open when commanded.
The culprit was the little OLED (or whatever it is) display. It looks to have failed, and when plugged in, pulls both I2C lines down. Why, when it failed, it caused all the valves to energise is unclear, but pulling it off brought the I2C voltages up with clock and data visible, and thus looks to have brought the unit back into operation.