I'm not familiar with your brand or model but the frost free mechanism usually works the same way on all models, at least here in the U.S. When you had the panel removed, you should have noticed one or two small (maybe 1/2 inch diameter, 5 inch long) light bulb lookin gadgets. These are actually heat lamps. The frost free device has a timer or perhaps an ice detector that tells the freezer to shut off and enter a defrost cycle wherein these bulbs light up, melts any frost or ice, the melt-water of which goes down the afore-mentioned drain. One or both bulbs have burned out. It's possible there may be another type of heat producing element, which has probably gone south on you. These are easily changed, once you locate the appropriate part number, especially since you already have acquired experience in removing the panel you discussed... Best of luck!