Alot of the times when a Cap like these go bad, the top gets domed or pushed out. This is a visual clue. I also look for heat marks on the board or corrosion. To check a cap using a Ohm meter on a multimeter, it should jump up to a number, and then slowly go down if it is bad. If it goes up and continues then it is good. Always reverse the leads after every test to make sure you got them right.
Diodes I believe will just crack open if they go bad. Atleast the one in the 32 in LCD did.