Post originale di: Minho ,
As C9679 points out, backlight issues are sometimes best resolved by clearing out the whole circuit. One thing I have found is bad coils do occasionally pop up. Sometimes they are cracked but still "measure" correctly but don't really behave as inductors. The only way to know for certain is to measure them with an LCR meter. I also had one situation where the chinese supplier I had ordered replacement coils from sent me the wrong ones. With no markings on most of the coils, you never really know what you are getting. In this instance, they were 1uH instead of 15uH and that messed up the circuit. As for the I2C lines, they are data lines so you need a scope to wee what they are doing. However, measuring them in diode mode can at least give you an indication of their overall state, such as shorted or no.