My church’s data projector stopped working, and since I was known to be an electronics engineer, I was asked to take a look at it to see if it could be fixed. The symptoms were very simple. You applied power and nothing happened -- no power, no LED, nothing.
I searched the manual and troubleshooting guide which told me nothing more than to turn the power on. The remainder of the troubleshooting section assumed the power was on and the unit was responding to its remote or buttons.
I decided to dismantle the unit. The assembly appeared to be designed neither for ease of assembly or disassembly. It seemed to be assembled by very cheap labor, where the cost of assembly was not a significant portion of the overall cost to manufacture the projector. After I removed the covers, the main board, the rear interface panel, and the cooling fan assembly, I was able to remove and check the input filter -- It was OK.
The next suspect was the power supply. With great difficulty, I managed to remove it and partially dismantle it to the point where I could unplug the input power cable and check to see if there was power. There was none. Obviously, there was a break between the filter and the power supply. Then I noticed, mounted to the bottom of the case, a suspicious-looking device with the power leads running through it. I removed it and discovered that it was an undocumented, resettable overload switch that was accessible through a small hole in the base of the case. When I pressed it, it gave a reassuring click and power became available at the power supply connector.
I decided to take a chance that this was the only problem and reassembled the unit. It worked perfectly again. I have to wonder how many units have been thrown out needlessly and how many customers have been charged exorbitant fees for repairs when the fix required the serviceman to simply poke a pin through a hole in the base to reset the switch.
This entry was submitted by Bill Washington and edited by Rob Spiegel.
Bill Washington has worked as an electronics design engineer in telecommunications and general electronics for more than 20 years. Prior to that, he spent more than 10 years in electronic equipment installation, repair, and refurbishment.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
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