With regard to no screen at all I have first hand witnessed doing the following for a quick remedy that works usually as weird as it sounds:
place the SCT Tuner in a freezer for 30 minutes or so. Take it out and fire it up. The change in temp on the LCD display will often times allow for temporary function of the screen long enough to get what is needed done. Saw a speed shop do this once on a customer SCT tuner module that powered but no screen when trying to load a tune onto the device. They completed the transfer from the PC to the unit, then stuck it in a freezer for half hour or so and the screen lasted long enough to complete the tune upload to the car with time to spare. That gave the customer a completed product and an option what to do about his tuner device....repair or replace.
As for inverted distorted characters that sounds more like a microprocessor that is responsible for screen control. If the replacement screen has the microprocessor piggybacked on the back of it the part may fix the problem, if it is merely the screen I am skeptical, but electrons have tricked me before on occasion.
