Irritrol 205TF Control Valve Question

We have a problem with our sprinkler system that weve tried to resolve through our local Irritrol dealer with no success. Weve reviewed past postings, but have not found anything that addresses our problem.
First, to describe our system: All 4 valves are controlled via an Orbit timer that is short of 2 years since being replaced and was working fine before this problem began. It seems to work OK on the timed system, except for zones 3 & 4, which is why we think this is a valve control problem, rather than a problem with the timer system.
We have 4 of the 205TF valves, with 3 in one box, and the other in a single box. The latter valve, which controls Zone 1, operates with no problems. In the other box, the drip system valve (Zone 2) operates OK. The other 2 valves, that control the rest of our lawn sprinklers (Zones 3 and 4), are where the problem lies. These valves work fine if the bleed screw is opened, but do not work when activated through the automatic or manual option on the Orbit timer. This would seem to imply that the problem lies with the timer, but as noted above, it works OK for Zones 1 and 2, and the Orbit manual does not have any Troubleshooting tips for separate zone failures.
We replaced the diaphragms on all 3 of the valves in the control box in question and tested all of the solenoids (which were all OK). When that failed to solve the problem, we purchased a Cover Diaphragm Assembly Kit (R205TFKIT) to see if there was some kind of a blockage on the inlet side of the valve. Weve also replaced the wiring from the timer box to each of the control valves. That too failed to solve the problem which is why we are asking for your advice.
So, our question is: What else can we do to figure-out a fix for this problem?
Thanks for your advice. Lee Phoenix, AZ
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Lee wrote:

Hi, First thing I'd try is reset the timer(programmer) and reprogram. If it does not make a difference, start switching valves between good and bad circuit, it'll narrow down the problem quickly. Trouble-shooting anything like this is based on simple logic.
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In additon to the above good suggestions, I'd point out that new sprinkler valves are available from a variety of manufacturers and are not very expensive. If I had a valve that would not open with voltage measured on it or was behaving intermittently I wouldn't waste time and money buying parts for it. I'd buy a new valve. You can even buy 4 of them already on a manifold. An entire new valve can be had for $15.
See if you have voltage at the valve with a VOM. If yes, get a new valve.
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