Most dot-matrix printers move the head back and forth at power-on, and check that the home sensor is working correctly. The fault light that you're getting could be a result of the carriage not moving at all. First check the carriage can move -- with the printer off, try sliding it along the rails. But I suspect the problem is electrical. The fact that the fault light comes on and blinks suggests to me that the processor circuitry is working correctly. Maybe it;s a motor driver problem. Maybe it's a loss of the motor supply voltage (which will be separate from, and higher, than the 5V logic supply. I think I'd start there. Trace out enough of the circuitry to understand how the motor driver works. THen see if it is getting power, and if it is, check the logic signals going into it.