[Radio Wrangler]

Around the time it was built, a lot of Japanese manufacturers used to glob a sort of slow setting adhesive stuff over components in their VCOs to reduce microphony. Since then, we've learned that the stuff turns corrosive and attacks components, especially a type of trimmer capacitor they also used around that time.

Symptoms would be sets going out of lock over part of the tuning range of one of their VCOs.

Most better performance radios split the tuning range across a few VCOs so each one had to tune a less wide range than a single VCO covering the full range would have to do. This translated into an improvement of the phase noise.

I don't know for sure that JRC used the brown glop in their receivers, but it's a good place to start looking. It's common in Japanese amateur radio stuff of this period to have to go into the VCO compartments, tediously pick out the hardened glop and replace the trimmers to get them working again over their full frequency range. This also means that the new trimmers have to be adjusted correctly so that the varactor tuning voltage stays within bounds over the tuning range of that VCO.

Note also that the tuning voltage going excessively low can sometimes stop oscillators oscillating that have no other problem. Not always, not guaranteed, but when you first run into this one, you can go round in circles trying to fix a VCO that was OK after all.

David