I love how the solution to so many of the Sherlock Ohms stories is something completely unexpected: an elevator in a building across the street, a cable buried in damp soil, someone using the microwave for lunch. What's even more interesting is how the individual Sherlocks suss out the solution.
One of my odd finds was a test floor with semiconductor ATE, that intermittently had a rash of failed devices on one test system, that turned out to be a very sensitive microvolt kind of test. A 600 LPM chain printer (the machine-gun hammer kind from the 70's) had a bad ground, and missing rubber isolators on its feet. Hammer noise from its chassis while printing in bursts was entering the raised floor grounding grid, passing underneath my test system, and radiating like a banshee before draining to earth via the nearest ground rod. When a printing burst coincided with testing the device on that sensitve test, the part was binned out as bad.
Calling a good device bad is the second worst thing a tester can do. Calling a bad one good is far worse.
I was in Air Force electronics training in 1963. One of the instructors told this story.
He was stationed on some South Pacific island. There were redundant radar transmitters and it was common for one to be down for maintenance. They had hired a local native guy to clean the floors and do general building maintenance. One day they were running the off line transmitter full power into a dummy load when they heard the door open, a loud scream, and the sound of smashing glass. When they went down there was a pile of broken flourescent light bulbs on the floor. They never saw the native guy again.
I was posted to this station a couple of years after this. The PDS's for several of the ATE stations had been moved back into the room facing the runway and the surveilance radar site. The new solution had been to cover the windows with aluminum foil to block the high power radar signals.Crude but effective.
My first computer was a RS color computer or COCO as they were called. The programs were stored an regular audio cassette tape drive. When I set up my computer and tried to load programs from tape, I would get random I/O errors. If it was a long program I would not be able to load it. I thought all my program tapes had been damaged in shipping. After a couple frustrating days, I was listening to the stereo, while working on the computer. The stereo emmiited a periodic buzzing approximately every 12 seconds. I was trying to load a program. Almost simultaneously the stereo went bzzt and the computer halted loading for an I/O error. Eureka! My apartment was on the 3rd floor of the building on the side facing the radar site only a couple of miles away. The period of the dish rotation was approximately 12 seconds. Every time the main beam swung past, the electronics in the apartment went crazy. Touch lamps would turn on or off by themselves. The TV cable box would change channels or turn itself on.
To fix my tape drive, I shielded it with aluminum foil. The noise was reduced, but I still had occasional errors. Within a couple of months, my final soultion was to move well away from the radar site. I hate to think of what that RF energy was doing to people who stayed in that building.
As to the flourescent tube story, we used to test emmisions by using a neon bulb. The bulb would lite up in the presnce of strong RF signals. You could even set off photo flash bulbs with the radar pulse.
This tale is not a problem that was solved, but rather a problem that was created, deliberately. I once worked for a developer of military electronics. Many of the engineers and techs would use the lab facilities to build home projects from scratch or kits during lunch hour. On fellow had just finished building an FM receiver and was starting to test it. Another engineer took a sweep generator, set it to sweep the FM band and hooked to a makeshift antenna. It was positions several benches away so as not to be noticeable. He turned it on while the FM receiver was being tested. The builder, hearing a 60 cycle (Hertz) hum, thought there was a problem in the power supply. He persisted a whole week in vain trying to find the problem. We finally turned off the sweep generator and he finished his projected. I don't thinkg anyone told him what was really going on.
Sure is a small world! Unsuprising that the PDS's were moved back into place, it is so much nicer to sit at a machine with a view. Sounds like you and I lived in the same apartment block in Grand Centre. Had the same problem with my Commodore 64 disc drives until I bought a pair of the Indus GT's.
I submitted a similar story about troubleshooting an HMI box on an off-shore drill rig. Could NOT find the cause of the system resets until the bay access door was opened one nice-weather day and we saw the radar dish swing past us every time the system reset. We added a conductive mesh to the NEMA waterproof door gasket and all was well. Darn RF!
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Good engineering designs are those that work in the real world; bad designs are those that don’t. If we agree to set our egos aside and let the real world be our guide, we can resolve nearly any disagreement.
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