I hope you have a multimeter with a dc clamp amp measurement. Use after you've checked all terminations.
Use your multimeter under full load or fault conditions at the controller,
Battery voltage is 12-14.4v?
Solar pv is 12-48v?
If these are correct remove
solar pv wires and short together, then use your clamp meter to measure the amps. Should be around 5-16 amps in dead short circuit, depending on configuration?
I would do this test together and separate on your
panels as you are saying one works. Maybe a solar panel is going open circuit?
Write down the measurements and if they are in range return controller to manufacturer for replacement.
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