In-ground lawn sprinkler: one zone out of five doesn't work

All of zone 2's 5 heads rise about 1/8", instead of 4", and water dribbles out. The flow through the water meter is about 1/3 lower than when the other zones are on, so at first I suspected a pinched/clogged line.
The odd thing is, that if any of the other four zones are on, zone 2's heads still rise the same amount, and the throw on the active zone is reduced because of pressure losses caused by zone 2 not being fully off. So zone 2 is never fully on or fully off. This sort of rules out the pinched/clogged line theory.
From the controller, I measured the DC resistance of all 5 solenoids; all the same. I replaced the diaphram in the zone 2 control valve (globe style); no change. The water passageway that the solenoid opens or closes is not clogged. There is no leakage around any of the valves.
In the house, there is a master valve on the supply line that opens if any of the zones are activated. I supplied 24 volts to it to keep it open. Then I opened each zone's bleed valve, one at a time. Zone 2's heads again rose just about 1/8". The other zone's heads rose the full amount.
One odd thing: in most of the zones, once I shut the bleed valve, the heads retracted after about 15 seconds, even if I didn't close the master valve. (That maintains the full water pressure to the supply manifold.) In one zone, however, the heads remained fully up even when I shut its bleed valve. The only way to shut the flow was the close the master valve by removing its voltage. (Maybe I didn't wait long enough.)
Question: Should closing the bleed valve while maintaining the supply pressure cause the valve to eventually close?
After writing the above paragraph, I decided to measure the shutoff times. I started with zone 4; it didn't shut off within 2 minutes, so I assumed it never would until I shut the master valve. Then I tried each of the other bleed valves. Now zone 4 always came on, along with the other zone (which, naturally, had reduced throw). I tried waiting over 15 minutes between testing each zone, master valve shut, and I opened the bleed valves to relieve pressure while waiting.
With two zones on, there isn't enough pressure to raise zone 2 heads at all.
So now the problem has expanded from zone 2 not rising enough, to zone 4 always on.
So confusing.
Thanks for your insights.
Ray
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Orbit brand parts (especially valves)?
Does zone 2's valve affect the flow rate at all? Or is it always the same dribble, regardless of bleeder valve/control setting?
These valves can sometimes exhibit odd behaviour. Unscrew the solenoids and make sure that the orifices aren't scarred up. In certain vintages of valve, the orifice can "slip" out of optimum alignment with the solenoid, and exhibit a variety of behaviours:
    - won't turn off     - bleeder does nothing     - bleeder arm jammed and cannot be moved     - won't turn on at all.
Try activating the solenoids after they're unscrewed and see if it actually moves.
I've also had a defective bleeder arm on a new valve that broke at a touch.
Orbit's saving grace is that they're _very_ generous with free repair parts.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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Chris Lewis wrote:

Don't know the brand. I don't see it stamped anywhere. It's a discontinued model, but replacement diaphrams are still available.

Always a dribble, whether opened by bleeder or solenoid.
I somehow got zone 4 to behave, so the only problem is again just with zone 2's head not fully popping. Now, zone 2 only dribbles when it's selected; it no longer dribbles when the other zones are selected.

It does turn off.

Bleeder works; causes dribble, just like when solenoid activates.

Don't have this problem.

Don't have this problem.

Before my first post, I had swapped solenoids; same symptoms. The problem is either in the #2 valve or the pipe from its output to the first head.
Since the flow, as timed at the water meter, is lower for zone 2, I suspect a pinched pipe, although there are no nearby trees. Perhaps there can be a break such that the loss of water through the break is great enough to keep the heads from popping (and releasing a lot of water), but low enough so the flow through the meter is low. I have to think about that. The soil isn't clay, but is slow draining.
Thanks for the input.
Ray
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