I will add 2 points to the above info:

1) Wave soldering is not inherently bad. There are other variables involved. The main problem is using a single sided (copper only on one side) circuit board vs. 2 sided. The 2 sided boards have "plated through" holes. These "suck up" solder and make a better joint. Single sided boards just have solder on the one surface of the board. This especially a problem for any parts that get hot. Cracks develop for the same reason that cracks develop in asphalt. The solder heats up and expands, but when it cools it is not flexible. After many cycles a circular crack will develop around the pin. This is one reason why surface-mount is so much more reliable than through-hole technology.

2) I strongly disagree with the advice to not add more solder. Ideally you would remove the old solder and add new with flux (flux core solder). As a second best option I would add some flux core solder. Old solder does not solder well. It becomes oxidized.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra