ThinWhiteDuke, voltage at Your Teensy in OK. Please check voltages at RX and TX pins of Teensy and on VCC, GND, RX and TX at the digitizer (bring some needles and probe to digitizer connector).
If You have 3.3v between VCC and GND at the digitizer board and 3.3v between RX/TX and any GND, that soldering should be OK. If any voltage missing, you may have problem there.
Checked this, 3.3v at everything compared to ground. I would like to do Bernard's suggestion, but I'm having trouble finding tutorials on using the .hex file. If advised I will do it.