Yes, 4.56kohm is about right. Here is my suggestion:
1) plug in a USB cable to the USB port, measure VIN-GND voltage and VCC-GND voltage, they should be about 5V and 3.3V respectively. The 5V may have some variations since USB power is often around 4.6 to 4.9V. So anything in that range should be fine.
2) if step 1) passes, then unplug USB, go ahead and plug in your sprinkler transformer to the orange terminal and test voltage again.
The reason I would suggest step 1 in your case is to make sure everything from the 5V to 3.3V conversion is working fine. Because USB power is internally protected, you don’t have to worry about burning anything. Once that voltage test passes, if something goes wrong in step 2, then it must be a problem with the 24V AC to 5V conversion. So this can help isolate the problem.