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| Vintage Fisher Receiver FM Tuner Repair. |
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| Arty30:
Hello All, I'm working on an early 70s Fisher model 301 Receiver. I've had it for a while and did a re-cap on it probably a year ago. I haven't used it since and pulled it out to test for selling. The amp sounds great however the FM tuner is exhibiting an interesting fault that I have not been able to track down due to my lack of understanding of FM IF and RF circuits. I can pick up stations, however the sound is non-existent in the strongest part of the station, but if I move the dial to either edge of the signal I get sound, but extremely distorted. it almost seems like the signal is blown out in the middle and edges to the point of peaking/saturation. at the same time though I have to crank the volume to hear these noises clearly. hopefully this makes sense and someone might recognize the behavior and know what to look for. I've spent a while testing diodes and checking signals with my scope but am none the wiser, I cant find an audio signal that is obviously good/bad. Th fisher also has a signal strength and center tuning meter, the strength works, center does not. I got a schematic from HifiEngine. Thanks Arty |
| Grandchuck:
I see you posted about this in the past and have the schematics. You could post the IF and FM detector sections here and perhaps get some clues from the gang. |
| Xena E:
Post the schematic here. It sounds as if your receiver is demodulating by slope detection, if it was fine when you stored it, there's possibly a fault with the ratio detector. Regards X |
| Arty30:
Here is a schematic, not the best resolution, but the silkscreen resolution on the board is somehow worse. |
| Xena E:
Check all components in the area shown in the attached. Start with C466 it is a common failure point in FM demodulators. |
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