SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I'm baffled by a problem with my 9 year old Rainbird 100-dv valves. I got in this mess because my pump was cycling on for no apparent reason. I isolated the problem to be in the irrigation system when I shut the gate valve leading to the irrigation from the pump. The cycling of the pump stopped and the pressure held steady for 6 hours. So I'm figuring that one of my 7 valves is leaking or partially stuck open. There was no significant leaking from any sprinkler head so I figured that I'd disassemble each valve and do the elementary maintenance, hoping that one of them will show itself to be the cause of the pump kicking on.
I did the first 2, basic stuff. Shut off water. Remove the solenoid and pull the blue screen out from the bottom and clean. Then remove the bonnet and diaphragm and inspect and clean them. No visible sign of any problem so I reassemble and hand tighten the solenoid.
Here's the problem, when I turn the water back on both valves are now stuck on and those 2 zones are trying to run at once.
I tried tighten the solenoid, thinking that was not screwed down far enough but that didn't help. The bleeder screw is shut off. I tried shutting power to the control box but that didn't help (I didn't remove the backup 9v battery).
Thinking that this couldn't be a fluke I tried another valve and sure enough same thing. Now I have 3 zones trying to operate at the same time.
I'm sure there's an explanation for this but it escapes me. Can anybody help?
Thanks in advance of your reply.

After replacing 4 of the solenoids I have the system working again. Still not sure of the cause but I have a theory.
Those solenoids were damaged somehow by lightning or a short and had kept the valves closed until I opened up the bonnet to inspect and clean. Once I opened them up they could not close because the solenoids were shot. So they remained open until I had the solenoid replaced.
Is that feasible?