My vacuum cleaner was faulty. I thought the reason might be blown fuse and I tried to fix it. Unfortunately, I could not find any fuse either in machine or connector. I then thought that the reason might be the faulty power control circuit. Therefore, I tried to bypass the control circuit by directly connecting power and motor. But it did not work. Finally, I successfully solved the problem by throwing the old one and buying a new vacuum cleaner :P I kept the power control circuit and tried to trace it when I was free. It uses a simple RC circuit and a DIAC to make a phase lag in firing the TRIAC. The circuit is quite simple and it is shown below.