555 timers can be really really cheap. Like 2 years ago, I ordered 50 of them for around 3€ on amazon. Today, I built a circuit, but it didnt work. So I checked the connections and tested every component with my transistor tester, but everything was fine. Finally, I got to the conclusion, that the 555 timer didnt work, which was the case. I replaced it and it worked.
To prevent this from wasting my time again, I soldered together this circuit (with sockel instead of 555), to test my 555 timers.
When both LEDs light up, the timer does work. If not, then not.
2 more of my timer didnt work and I am glad that I built this thing.
