One day i went to my refrigerator and my compressor was working like it was being turned on-off really fast then internal klixon cuts the power to compressor so i tought compressor died, i searched the web to see how i can wire it directly to mains and so i did and it was working fine. then i checked the electronics first thing that came to my mind is that power supply of the electronics has gone bad and it was one of those capacitor power supplies so i said great ill measure the capacitor and it will probably be half its value but it was 1uF spot on. and this board is as simple as it gets 5v supply for the micro controller, triac for compressor, voltage divider for NTC probe with potentiometer to set temp. i have used those cheap light dimmer circuits to check triac it was ok, 5v supply with mutimeter ok, so i said oh great micro controller has gone bad but then in desperation i hooked the 5v rail to oscilloscope and it had some weird shape 50hz i don't even know how to call it wave so i went to measure electrolytic it checked ok on capacitance and since i don't have esr meter i just checked it with multimeter set to ohms and it checked ok. i checked 5v1 zener out of circuit it was ok. now it was really getting weird i put everything back on the board and supplied 5v from my bench PSU and board was drawing steady 11mA and as soon as i hook up 220v to it the power supply is not working properly so i bought 1uf 275VAC changed it, not working, changed electrolytic and what do u know board started working.
now my question is what went wrong with electrolytic cap so that when i applied 5v directly across it, it was working and when its in circuit it was failing and what instrument is capable of measuring this fault esr meter ? capacitor was looking brand new no bulges or anything
here is the board in question
http://www.supremeplumb.com/imgs/fridge_freezer_spares/BSH265109.jpg