You probably know the first part of this story:

A production line was giving problems that the regular operators were unable to solve.
So an expert was called in. It was a gentle guy, grey hair and he his services had been called upon for as long as anyone remembered.

He spent all day talking to people in the factory and at about a quarter to five, he went to his car, got out a tiny case and walked to a part of the production line.

He opened the case and out came a small hammer made from polished stainless steel. A hatch was opened and the old guy crawled underneath the machine. A clunk was heard as the hammer struck the machine's guts, and the production line got back to its normal operation.

The next day an invoice arrived that specified:

- Repairing production line by tapping with a hammer Eu 5,--
- Knowing where to hit Eu 1500,--

After a while the old problem returns. Unfortunately the old guy has retired and moved to another country. Sven is called in.

The people in the factory know where to look but not where to hit. They point Sven in the general area and he crawls inside the machine with his small hammer and a torch.

About 15 minutes later a clunk is heard and everything turns back to normal.

Would it surprise you if I told you this is actually a true story?
The setting is a bit different though.

The production line is actually an energy to motion conversion unit known as a car, the old guy was a worker from the auto club and I did not have to pay because I was a member.

But he did give a tap with a hammer somewhere under the hood of the car, everything did return to normal and I did not see where he hit.

And sure enough the problem returned as he had predicted. I knew I had to hit something under the hood of the car but I did not know where. But since I am blessed with remarkable perception (no, this is no exaggeration) I found the spot. I tapped once and everything returned to normal.

Later on I learned that the cause of the problem were worn out brushes in the alternator (or something similar). It prevented the battery from being charged which made the lights go out and the wipers slow... Hitting the alternator gave the brushes a jolt that got them back to work for a limited time.