Design Con 2015

Soldering at sea

-September 27, 2013

Tales from the CubeIn my early days as an electronic technician in the US Navy (circa 1977), I was once working in the test equipment repair shop on my ship late during a duty night. Some engineers or scientists were on the ship that evening measuring the heat and humidity in the ship’s boiler room when their main piece of monitoring equipment failed. Naturally they brought it to the repair shop. We took pride in being able to repair anything and everything electronic on the ship, but I had never seen anything like this rig; neither had my supervisor.
 
All I remember was the main electronics unit was fairly small for test equipment at the time, about the size of a bench-top, portable VTVM. Then there was some sort of spherical transducer that, I think, picked up the temperature, humidity, and radiated heat. The engineer that brought the unit into our shop had the tech manual so we went about the calibration procedure it contained. We had access to voltage standards, current sources, resistance standards, and every possible type of precision electronics measuring equipment in the calibration lab next door. At the time we were assuming the spherical transducer was okay, or at least we hoped so.
 
Tales from the Cube submissionsSure enough, the electronic portion of the equipment did not pass the calibration procedure so we opened up the unit and checked the signals using the schematic diagram also provided with the manual. In short order we found the probable faulty component, which turned out to be a Darlington pair transistor in a single, 3-pin package. I had never heard of a Darlington pair transistor, but my supervisor had. Of course, we didn’t have that transistor in supply on our ship and we were both disappointed that we couldn’t help these guys out. We didn’t want the visiting engineers to presume we were a couple of no-load sailors that couldn’t get the job done.
 
So the visiting engineer comes up to our shop and listens to our story. He was actually pleased we had gotten as far as we had. Then he says, “Isn’t a Darlington pair just two transistors connected in a single package to multiply the two beta values for higher current gain?” Yes, we responded. “Why don’t you just get two transistors similar to the two in the Darlington pair package and connect them together?” My supervisor and I looked at each other and agreed that it was a good idea, and wondered why we didn’t think of that.
 
Read more Tales from the CubeOff I went to the supply department to requisition a couple of transistors that we identified from the Transistor D.A.T.A. book. The engineer showed me how to solder them together to achieve the Darlington pair configuration. I kludged the conglomeration in place of the failed part as neatly as I could. When we powered it up, it worked great and passed the provided calibration procedure. The visiting engineers finished their work on schedule. The next morning our Division Officer was pleased, but not half as pleased as we were when that piece of test equipment worked properly.

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Steve Goss received his electronics training in the US Navy and at the University of Maryland. His 35-year career in electronics has primarily been with stabilization controls. You can read more about Steve here.

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