As mentioned before, having voltage and no supply of current
is often caused by connections with a medium to high resistance.
Maybe another way checking the panels without the controller is:
get a load, ie globe 24 Volt or even a 12 Volt one (but that may blow), and check if it lights up (when connecting to one panel output). If the globe lights up (or blows) then you have Voltage and Amps.
If you did the above with new wires directly from the panel, and you have Volts and Amps on each panel, then your existing wiring
If you are still having problems than the fault is inside the control (junction) box or the panel itself. Is there a diode fitted in the control box
? Check that diode or bypass that for such test.
Edit: I see that while I was writing this, previous posters referred to diodes as well.....