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I recently found this radio which I dont know when it was made. (date code is 5241), and the FM band does not work. AM works fine but once I turn it to FM all that happens is a low speaker hum. I tried different stereo modes and the oscillation switch but it stays the same. Is there any way to fix this?
Questa è una buona domanda?
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Hi @rubix_cube ,
According to this webpage your radio is a boombox from the 1980’s, so most probably it will be an all transistor radio, i.e no valves, which makes it easier to get replacement parts if it turns out to be a faulty transistor.
Use an Ohmmeter to check that there is continuity between the extendable antenna and where it is connected to the circuit board. Usually with these types of radios, the AM antenna is a ferrite rod type inside the case, whereas the FM antenna is an external one. Either an extendable one such as yours has (see video of your model) or a wire hanging out of the case,
Also a quick check of all the capacitors in old radios is nearly mandatory as they are prone to leakage over time, although since the AM works in the radio, you may just have to check around the FM antenna coupling/ tuner/oscillator section.
Have you opened the radio up at all? Sometimes with older radios the circuit diagram is to be found on the inside of the case which would be a great help
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I did open it up and looked, no leaking capacitors from the top view just some dust. I did not disassemble it any further. It did not have a diagram inside and the fm antenna is an extendable one. I was thinking of replacing the antenna as it was bent but the screws are old and as soon as I tried they corroded and I could not remove them.
Also, based on some images I believe the fm tuner section was on top which is the view I saw. https://goo.gl/images/pZSPFW
It was an area that looked like this.
Hi @rubix_cube ,
When I said capacitors had leakage. I didn't mean leaking, I used the term which is used to describe when capacitors become more like very high resistance resistors and there is a DC current "leakage" path through the capacitor, which normally isn't there and alters the value of the capacitor. You need an ESR meter to check if the capacitor is OK or not.
You could also try looking at the FM selector switch, which may be a multi contact switch.
A quick and dirty fix may be to spray the switch with this -example only and check if it fixes the FM problem
Reading through this link also seems to suggest that the switch may be the problem for no FM. (see the section entitled "And After... " (you have to join to see the images ;-(
You can replace the antenna with a length of wire as a test to see if it will pick up FM (after you've cleaned the switch ;-)
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You may have to take to radio to a technician who can align the tuner. It takes a special person who knows how to do this with specialized electronic testing equipment. If it is a vintage tube radio could be a bad tube that is keeping it from bringing in stations. Make sure sure you also have an FM antenna connected to it.
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At my cheap old international HPSS radio the problem was the broken cable connecting the antenna to the main printed circuit board (PCB) !!!
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I looked and it was fine, this is old so I already got rid of the radio. It ended up not working at all after a while and didn't even turn on with batteries or plugged in.
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