Monday, June 29, 2009

Recycled AM/FM Alarm Clock Radio

This is a vintage ( circa 1980s, based on the date marked on the IC chips, in fact 1983 ) 7 segment LED alarm clock radio that I decided to give a new lease of life. The clock portion is bad as the time setting switches are stuck and the clock cannot be set. Other than that the AM/FM radio portion seems ok.

I hooked it up to a larger 2-way speaker and this gives a much clearer and richer sound. The piano sound just perfect. The sound stage is excellent for a desktop radio.

The reconfigured AM/FM radio show signs of trouble after a few hours of use with the new speaker. Some testing reveals a dried out capacitor and a bad transistor. The transistor is used to turn on the radio via the clock or a switch. The fault prevents the power supply from reaching the radio circuits.

The capacitor is replaced and the transistor removed and the radio connected directly to the DC power supply. The radio is now working perfectly.

Note the rather small AC step down transformer. The radio may not have been design for prolonged use ( maybe as bedtime listening only ), after a few hours of use the ac transformer is hot to the touch. Also load regulation of the output voltage is bad. Note also the rather black look of the varnish on the transformer which is the result of prolong use.

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