DIAGNOSIS Internal leak. The water condensing on the cold coils is supposed to drip into a drain pan and then flow to the bucket or pump. If that drain pan is cracked, or the internal drain tubes are disconnected or clogged, water will drip inside the cabinet and out the bottom.
FIX Unplug the unit and move it to a place where you can work. Tip it on its side (gently) and remove the bottom panel. You'll likely see mineral deposits or mold tracing the leak path. Look for the white plastic drain pan underneath the coils. Check for cracks. Also, trace the short tube that leads from the pan to the pump or bucket inlet—make sure it's securely attached at both ends.
IF THAT DIDN'T WORK The leak could be from the condensate pump itself if the housing is cracked. Or, in rare cases, if the unit was overcharged with refrigerant, the evaporator coil can frost so heavily that ice blocks the drain pan and meltwater overflows. Thaw it completely and check the drain path again.
HEADS UP Before reassembling, do a water test. Pour a cup of water into the drain pan (where the coils drip) and watch where it goes. It should flow cleanly to the bucket port or pump. If it leaks inside the cabinet, you've found your problem spot.