FYI, in case anyone else runs into this same problem. My tablet got dropped while the charger was plugged in. At first it didn't appear to have been damaged, but the next day the battery was dead and the red charge light wouldn't come on. I disassembled it and found that the charging jack is soldered to the circuit board at 4 places. Three had broken off, one of which had actually peeled the circuit trace off the board. I could solder 2 back on, but the 4th was no way. I checked the polarity of the jack by removing it from the board and plugging into the charger and using a multimeter. Two terminals were positive, two were negative (but no continuity between the two). The one that had pulled off the trace was a ground, so I ended up soldering a wire to the jack and then soldering the other three points back to the board. I then ran the wire to the battery connection and soldered it into the ground circuit there. It charges fine now and has worked for weeks.