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I recently had a failure on my OpenSprinkler v3.2 AC model after many months of reliable operation. I traced it to a shorted D2 Schottky diode on the output of the 1509 regulator on the power board. That’s the freewheeling/flyback diode for the buck convertor. Has anyone else experienced this problem? Any ideas as to cause? Mains power is usually pretty clean in my area, so I have no particular reason to suspect external spikes. Also the 1509 regulator and other PS components are fine.
I woke up to the same problem today. I don’t know of any specific cause, other than the temperature in our garage being extremely hot the last few days. I could feel D2 getting extremely hot. Did replacing D2 solve the problem for you?
To verify if it’s indeed the issue with diode D2, you would have to desolder it from the board and test its forward voltage drop. The diode is very robust so it’s quite rare for it to fail. I suspect the issue might be somewhere else, like a shorting somewhere else that’s causing an over-current situation with D2 and hence it becomes hot. I recommend you to measure VIN (i.e. +5v) to GND resistance. It should be a minimum of 4 to 5K ohm. Otherwise something on the +5V line is shorted.
I desoldered D2 and it measures roughly 1 ohm in both directions. My DMM doesn’t have a diode test mode, so just testing with resistance mode. The main controller board boots up if I remove the power board and connect 5V/GND. Since the diode is effectively a short circuit, it seems to definitely be damaged. I don’t know the cause of the problem though. I’ll do some more testing.
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