Hi, everybody,

Let me start from the begining:
I bought a kit with a AM and FM radio for me to study signals on the oscilloscope and Signal Generator. I assembled the radio and it was working fine. So I decided to check the waves in the oscilloscope. After I work a long time trying to get the clipping voltage or F3db or make the voltage drop from 2VP-P without success the radio AM stop working. I started to check everything from resistors to the IC LM386 and here is what I found out: Voltage drop from 9 Volts to 376 mV. I check the Ampers in the battery input. Should be less than 10 mA and was 1.39 Ampers!!!
Current without de IC 2.5 Microampers. Voltage approx 900 mV. When I change to FM everthing go back to normal.
The radio is the Model AM/FM-108K Radio Kit from elenco. Schematics and Manual in attached file.
:? Can anybody help! please.

John

Attached Files

amfm-108k.pdf (937.2 KB, 22 views)

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JRR

 

I would say U1 the LM386 is shorted. That looks like the only thing that can draw that much current unless C39 is shorted. But that will be on AM and FM. You said AM stopped. Is FM still working through the speaker? IF U1 is on a socket, pull it out and recheck the current.

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\"You can\'t make a circuit fool-proof, cause fools are so ingenious!\"

 

Without the LM386 the current is 2.5 microampers. I changed C39.

Thank you again.

John

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JRR