Originally Posted by
aberry
Diode drivers don't regulate voltage, they regulate current. There will not be an output voltage adjustment at all unless there's a step-down converter before the constant current stage, which there isn't on your module. Since you only have one pot per channel, that's going to be a TTL driver (on/off only, no intensity control) and the pots will be your on current adjustment.
Most likely your diode is just dead; low output even at nominal current is a reasonably common failure mode. It's possible that it's a problem with the driver, like perhaps poor connection between the wiper in the pot, in which case MAYBE tweaking it will get you somewhere, but more than likely trying to turn the current up will just make it more dead, especially if you try to do so without any idea how much current you're already giving it.
You can monitor the diode current by measuring the voltage across the current sense resistor (circled below). Since that's a 2R resistor, divide the voltage by two and that's your current. (The blue also uses a 2R resistor, so same goes for it, the green has a 1R, so the voltage reading is the current reading.) If it's more than, mmm, 150mA? then the diode is dead. If you choose to replace the diode, then be sure to set this current well below the maximum indicated for the new diode before hooking the new one up.