- Make sure to verify that there is no short circuit in one of the head coil in the particular printer head(in case you don't know, printer head on all dot matrix printer consists of small coils inside),otherwise it will damage the driver transistor(s) of the logic board in the good printer. Tests all pins of the printer head by using a multi tester(analog), try to find out if there is no two pin that is short circuit(zero resistance), or if you have another good printer head, try to compare the reading with the suspected one.
- Test all head driver transistors of the logic board, before installing a good printer head, otherwise it will damage the good printer head and you will now have two defective printer head.You can check the head driver transistor by comparing all reading by way of a multi-tester(Analog) each one of them should have the same reading. If you suspect that one of them is defective, remove the transistor from the pcb and perform a standard transistor test to confirm if its bad.
If no short circuit exists on both head and logic board, it is now safe to proceed in swapping printer head to and from a good printer unit.
Note: Head driver transistors are the one supplies electricity to each one of the coil in your printer head, these transistors are normally located in one place within your printer logic board, the number of transistors corresponds to the number of your printer head pins.