Electronics > Repair
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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