Where I used to work, there was a photo typesetter. This machine would regularly blow a 20-amp fuse, resulting in a service call, lost time, and lost money. The service technician would come by, fiddle around, replace the fuse, and leave a sizable invoice for repairing the machine.
I studied the typesetter and discovered what the actual problem was. While the fuse was rated for 20 amps, the fuse holder was not. I called a friend who had a similar machine and had been having the same problem.
The next time the repairman came to fix the machine, I asked him if other machines had a similar problem. He said ours was the only machine he serviced that had the problem. When I mentioned the machine my friend had, which he also repaired, the repairman became very upset. I told him that the problem was the rating of the fuse holder, not a failure of the machine.
I suggested that a larger fuse holder and a physically bigger fuse would solve the problem. He became even more upset and told me that was the way the machine was built, and that neither he nor I could change it.
I replaced the fuse holder and the fuse in the machine where I worked. I did the same thing on my friend's machine. We never saw the problem, or the repairman, again.
This entry was submitted by Howard Gorin and edited by Rob Spiegel.
Howard Gorin repairs ophthalmic instruments. He is also a second source for repair parts for the equipment he services. He is connected with the Charles River Museum of Industry and Innovation.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.