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Hi pitch tone on old AM car radio

I have an old, original AM car radio c 1972 installed in a MGB. The radio is marked Bendix 2BAMBL. Since it's the radio that came with the car I'm trying to fix it.

The unit powers up OK. When turned on it ''squeals''...probably 3Khz to 5 KHz tone. The audio amp works. I can find and hear one or two AM stations very weakly (they are local stations so should be OK).
The radio schematics are available online thru Sams but before I lay out $30 I'm just wondering if a knowledgable AM radio receiver person could suggest possible problems. Could it be something with the IF section?

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  • Anonymous Mar 25, 2009

    I have a high pitch tone that comes on my fm stations in my 1991 stealth



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Having a high pitch whistle shows that the unit is somewhat unstable somewhere in the circuitry causing it to oscillate where it shouldn't, due to one or more components going faulty. What I would suggest is open up the unit, clean the circuit board thoroughly and replace all the electro capacitors with ones of same value, sometimes problems occur in radios this old because the capacitors dry up, like oscillation may happen if the capacitor that is used to smooth the voltage that feeds the automatic RF gain loses value or goes open circuit. Sometimes IF transformers can go open circuit at random (which can cause oscillation and weak signal too), and so do transistors, which can be hard to track down unless you have an oscilloscope?!? Are there any cracked soldering joints? to check for dry joints; use a plastic tool to tap, press, and rub on the solder side of the board. Having all the gear??? You go through each stage to see if it is working properly. Dont fret too much if you cant fix it yourself due to not having the gear, sometimes multimeter measurements may help, and also blindly poking your finger around... maybe, but it is very challenging and does not find all faults, if you have any friends who are Amateur radio operators, they would have the gear to help you as they always tinker with radios and actually make some of their gear, otherwise I am sure that TV repair persons are fully qualified to fix it for you, with a price! have fun ;)

Posted on Apr 01, 2009


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