Observe the Filter Capacitor Cap
Whenever there is a problem in electronic equipment i would first look at the electronic board for dry joints, decayed glue, loose connection in connectors, bulged capacitors, burnt resistors (some resistors just change colour), rusted lead in components, oil leaked from filter capacitors and etc. Sometimes we as electronic repairer could “missed” the bad components especially the components that had been covered by shrink tube sleeve, plastic cap (look at the picture) and etc.
One must be sensitive to the surrounding otherwise if you have missed just one component, the rest of the troubleshooting time would be lost! If possible, you can tear open the shrink tube sleeve to see if the components is in bad condition or not. This happen many times in the metal oxide varistor (MOV) in power supply circuit. If you don’t want to peel off the plastic cap you can straight away replace and retest the equipment again. Sometimes a slight swell in the top of the capacitor will cause the power supply to malfunction. Surprisingly this type of problem capacitor was tested good with ESR, digital capacitance and analogue meter. Train yourself to look at problematic board and i’m sure one day you will be an expert and you will miss “no more” bad components.