Sometimes electrical nuances are tricky. When you test the resistance to the valves from the clock as Wet Boots suggested, be sure it's 20 Ohms or more on each valve solenoid. Different solenoids (brands) have different resistances. Most are 24-25, 45 more or less, and Toro is generally 55 Ohms per.... Wire lengths can add an Ohm or two depending on distance from the clock.
Check continuity across from 1 to 2, 1 to 3, 1 to 4 and so on. Each should read twice what the common to valve resistance is. This would tell you the HOT connectons to the valves are OK or not. If they are all in the same ballpark, I would seriously consider re-doing ALL OF THE COMMON CONNECTIONS in the circuitry.
One last thing... when testing the solenoids and valves, defeat the rain sensor by jumping the terminals.. it might be shot.
The Irrigation Specialist Mfg' Az.
Please check my website and you'll find what I do and the unique tools I make and market.
Real timesavers, especially the Suck-Tube and Krik-It.
http://www.tismaz.com