Back in January, I replaced all my solenoids (a couple had locked up, and in for a penny...) and the control panel, and everything was hunky dory for the two weeks I ran the system putting in the winter grass.

I recently decided to overseed again with a new seed, and now the system won't turn on any of the solenoids.

I checked the panel, and it's passing around 28-29V at each zone terminal when I activate that zone, just as expected.

I pulled a solenoid, thinking they had died again, and it tested fine when I applied power to at the control panel.

Going back to the irrigation valve end wiring, the solenoids I tested are only getting 9-10V each from the wiring. I tested them all, and they're all receiving around that voltage.

What am I missing? If it was no voltage, I would suspect a wire break.

Assuming the voltage was okay when installed, check for corrosion where the wires attach to the control panel, or at any splices along the runs.

It could be normal voltage drop due to the wire size being too small. The longer the distance, the larger the wire will need to be.

The high resistance due to corrosion is a good sanity check.

Bad component pulling high current could cause a voltage drop, but with new solenoids seems unlikely.