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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Today's 'what the heck is it?' item...
Hello all...
I was cleaning up some stuff in the basement when I found a cardboard box with a Newsweek address on it. Opening it revealed a small white-cased device with an on-off pushbutton and a speaker. It uses 4 double-A batteries. There are no other controls or indicators on it anywhere. I first thought that it had to be some kind of a fixed-frequency radio, probably something that was tuned to one AM station for promotional purposes or maybe even a weather radio. But it doesn't seem to receive anything--assuming it even works. With batteries in place, it would hum (much like ground loop hum) and the sound would get louder near electrical wiring. I never heard any sort of station or static. Taking it apart revealed a very simple circuit board with a coil, power switch, a few small transistors, some resistors and a few caps. It's really very simple--too simple to be any kind of radio I'd know about. The one IC on it is an STMicroelectronics TBA820M audio amplifier, with a date code of early 1988. Running it while taken apart revealed a few things--let the circuit board get near the battery compartment or wires, and the speaker would go into feedback. The coil on the board was sensitive to touch or metal tools--and produced a "tapping" sound in the speaker when touched. It was not sensitve to other random objects on my workbench. I also found that I could feed audio into one of the connections on the coil and hear it clearly through the speaker. A picture of the circuit board is he http://greyghost.mooo.com/newsweek-radio.jpg (541x255, 47KB) William |
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