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Old 29th Jul 2018, 3:45 pm   #1
paulsherwin
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Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Roberts R606 MB VHF distortion

I'm completely flummoxed by a fault on an R606MB. FM reception becomes distorted and sibilant when the signal is strong. Pushing in the telescopic aerial to reduce the signal strength eliminates the distortion.

I can't find anything wrong with it, and don't understand how these symptoms could be caused given the way FM works. All the RF/IF voltages seem plausible. The discriminator electrolytic tested OK but I changed it anyway, ditto the discriminator diodes. No improvement. I changed the BF194/5s, not specifically to fix this fault but because I now always do it anyway as a precaution. No improvement.

I'm sure I must be missing something obvious. Would anybody like to point me in the right direction? The radio is working well apart from this fault.
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