Valves can be located with a Progressive 521 wire and valve locator or other similar device. The fact that your getting some water through the valve indicates either a leak in the zone whether in the heads or the piping, or the valve is malfunctioning which is probably the issue. It could be a weak electrical current getting to the valves due to a bad timer like you said, but from everything that you have mentioned, I don't think it is the timer. In my opinion the timer is probably not your issue.
If you do need to get a pro involved check them out with a Local BBB and ask them if they have a valve locator and if they use a multimeter to diagnose electrical issues.
Good Luck
P.S. These types of issues are usually over the heads of the average home owner, and the average sprinkler repair guy!!!!
You need an expert.
If you are in the great state of Texas you need a Licensed Irrigator that Specializes in Repairs not Installs!!