Well..yes... I bought this used on eBay...
When I received it I noticed a strange sound when tilting on it, like something was loose inside, but the unit seemed to work ok, so I didn't worry.
But now, since the master valve didn't work, I opened it up and immediately understood why it didn't work and why there we're something loose inside!
The loose part was part of a blown transistor++!!!
So, to make a long story short:
I have done some soldering work and replaced some components for the master valve output using parts from an unused zone output. My rachio now works fine, including the master valve output, but I only have 5-6 working zone outputs...
If anyone has a component list or detailed schematics I would be very happy as I'm not able to identify all components.