1 of the sprinkler zones won't turn off. Turned panel to off, disconnected wire towards valve at panel, zone still spraying.

Only way to stop it was turn off water at main valve

Replaced solenoid and valve diaphragm. Still spraying.
And now valve box full of water. This is an old system so no bleeder screw at valve

Thoughts? Dig up the area, expose and replace the valve? (Not my ideal Sunday task but oh well)

I just had same problem and had to replace the valve

If the valve is still made, you can try changing the bonnet (top) before you cut the valve out and do all the digging. I had one that wouldn't shut off; the diaphragm alone didn't fix it, so I tried changing out the bonnet and rest of the topside parts and it fixed it. I assume there was a crack in the solenoid bleed passage in the bonnet. May save you a bit of digging and the associated frustration of changing the entire valve.

If you have to replace the valve that would be a good time to add a ball valve isolation valve on the supply side of the valve so that you can isolate it later should you need to make repairs and you don't have to kill the whole system.

Dumb question but did you twist the top to make sure you havnt accidentally manually opened it? If you have, it will run regardless of the state of the controllers or electronics.

Give it a twist anyway and see if maybe it's hung up. Maybe you can kick the project to next Saturday?

Fixed it yesterday.

Turned out to be the diaphragm.

I pulled the valve cover back off and I had incorrectly positioned the new one the first time I reinstalled the cover. Must have knocked it out of position somehow.

Anyway, I properly positioned the new diaphragm and we're good to go

Thanks for all the input though