I'm partners in a sailboat (a T-bird 26). It's been having mold/moisture issues, and I've been tasked with creating a fan to circulate the air in the cabin. I have a couple old 12V computer fans, but they draw about 200 mA, which would ultimately drain the boat's battery ahead of the solar charger's ability to keep it charged. So I designed a 555 circuit to let the fan run for five minutes and rest for 20 minutes. It worked great on a solderless breadboard. But when I soldered up the circuit on a perfboard, it refused to start the fan.
It turns out that the problem was leakage current, due to residual flux between pins. I'm using a 3300 uF cap, along with more than 500K total charge resistance. Without adequately cleaning the board, the charge on the cap would never exceed 5.41V, and it takes 8V to turn the fan on. After meticulously cleaning the board with isopropyl alcohol and a toothbrush, plus an X-Acto knife between pads, the circuit works fine now.
I probably should've just used a BS2, but I had an NE555 in the scrap drawer and wanted to do things on the cheap. Oh, well. Lesson learned.