Hi all,

I have a Rain Bird ESP-Me irrigation system with five zones. That's one more zone than the base module has so I have a three zone expansion module. I noticed last year that the last zone sometimes did not run. After doing some basic troubleshooting I sort of figured out that when the weather was hot (control box in unconditioned garage that gets quite hot) that last zone would not run. The error code on the ESP-Me controller simply said "No Module". If I removed the module for a bit, let it cool, then put it back in it would run. I then started leaving the module unplugged when the system was not actively running, and it works fine. Obviously that is less than ideal.

I had left it plugged for a couple "extra" hours yesterday and could feel that the plastic expansion module case was somewhat warm when I finally remembered it even though it was a cool day. Quickly opened it up and found that the L7905CV voltage regulator was pretty darn hot.

So, this leads me to think something somehow the VR is overheating and then not supplying the rest of the circuit, causing the controller to think it's not there. Maybe the VR is bad? I can't see anything in the circuit that looks amiss at all, and I would welcome your eyes on it. I verified the incoming 24VAC from the wall wart. It's a bit of a tear-up to get to the four module interface connections.

Edited to add: I do have some VR heat sinks, and one might just clear the case, but that seems like a patch.

Thanks

 

I would Lift one of the regulator pins and check the current on the output pin.

 

You can also test in isolation in diode mode using your DMM.
Desolder the output pin (Which is the 3rd pin furthest from the shiny gold contacts at the top of the module)
Do two readings, one with the black lead on the output pin and
red lead on the ground pin and then for your next reading switch the leads.

If you get a reading of 0V or close to, in both directions then its shorted.
It sounds like your VR output pin is exceeding the current threshold and the
internal transistor goes into a thermal shutdown. Once cooled down the VR
then resumes its function until it becomes too hot.
Also installing a heat sink on a new VR sounds like a win and def wouldn't hurt.

 

I ordered a replacement VR and am waiting until I have it on hand before digging into the existing one. Will report back.

First time running into a negative VR, happy to add another component to my list…

 

Note that the pinout of the negative regulator is different from the positive regulator. Even positive regulators can be different. Always check the datasheet.