FM radio distortion problem. - UK Vintage Radio Repair and Restoration Discussion Forum

Hampus · 18th Apr 2021, 8:29 pm

My trusty old National-Panasonic alarm clock radio is sounding progressively worse. Of course it has never been a Hi-Fi radio but now there is noticeable distortion.

It sounds like when you turn up the volume too high on a transistor radio or when you hear an FM station slightly out of tune.

Since it has been detoxicating for a while, can it be because of dried-out capacitors? Do transistors go bad in this manner?

Radio Wrangler · 18th Apr 2021, 9:29 pm

One thing off the beaten track is a dried-up electrolytic that gets forgotten about, the floating one at the end of a ratio detector.

David

Silicon · 19th Apr 2021, 2:38 am

Make sure the speaker is OK first. It could be rusty or the voice coil may be rubbing.

Can you connect a good speaker to the amplifier output?

Is it distorted on the Medium Waveband?

Hampus · 24th Apr 2021, 7:52 pm

Thank you for your thoughts.

It turned out to be easy to fix, i opened it up and made some measurements and I immediately found a clue in that the DC rail voltage dropped by about 30 percent when the radio was switched on. I replaced the electrolytic smoothing capacitor and all was well again

Regarding medium wave we don't have any such transmitters in Sweden anymore and I could only find one, noisy station on that band.

18th Apr 2021, 8:29 pm	#1
Hampus Pentode Join Date: May 2010 Location: Sandviken, Sweden Posts: 233	FM radio distortion problem. My trusty old National-Panasonic alarm clock radio is sounding progressively worse. Of course it has never been a Hi-Fi radio but now there is noticeable distortion. It sounds like when you turn up the volume too high on a transistor radio or when you hear an FM station slightly out of tune. Since it has been detoxicating for a while, can it be because of dried-out capacitors? Do transistors go bad in this manner? Attached Thumbnails

18th Apr 2021, 9:29 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: FM radio distortion problem. One thing off the beaten track is a dried-up electrolytic that gets forgotten about, the floating one at the end of a ratio detector. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

19th Apr 2021, 2:38 am	#3
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,171	Re: FM radio distortion problem. Make sure the speaker is OK first. It could be rusty or the voice coil may be rubbing. Can you connect a good speaker to the amplifier output? Is it distorted on the Medium Waveband? Last edited by Silicon; 19th Apr 2021 at 2:39 am. Reason: Another question added.

24th Apr 2021, 7:52 pm	#4
Hampus Pentode Join Date: May 2010 Location: Sandviken, Sweden Posts: 233	Re: FM radio distortion problem. Thank you for your thoughts. It turned out to be easy to fix, i opened it up and made some measurements and I immediately found a clue in that the DC rail voltage dropped by about 30 percent when the radio was switched on. I replaced the electrolytic smoothing capacitor and all was well again Regarding medium wave we don't have any such transmitters in Sweden anymore and I could only find one, noisy station on that band.