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Old 23rd Jun 2020, 8:53 pm   #1
Sackville
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Default Japan Radio Company Receiver NRD-525G

Hi everyone, my name is Sackville.

I wonder if anyone could help me with a problem I have. A couple of months ago I bought a JRC NRD-525G from a friend of a friend whose father had passed away. The problem I have is that it works perfectly well on frequencies from 7.287.00kHz but as soon as you tune below that frequency ie 7.28699 and lower there is no reception whatsoever.

Any ideas would be greatly appreciated.
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Old 24th Jun 2020, 5:20 pm   #2
Jon_G4MDC
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Default Re: Japan Radio Company Receiver NRD-525G

There are 4 oscillators in the PLL and 7.287MHz is the edge frequency for switching between VCO1 and VCO2.

Your VCO1 is therefore not working. The board is CGA131 and known as Loop1.
The VCOs are inside a screening box on that board. I found this out by going here.

http://www.radiomanual.info/schemi/R...D-525_serv.pdf
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Old 24th Jun 2020, 9:43 pm   #3
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Default Re: Japan Radio Company Receiver NRD-525G

Thank you Jon G4MDC for this information, i noticed when tuning down from 7,287.00 to 7,286.99 the led marked (unlock) on the loop1 board illuminates. My expertise is in TV servicing so this is a bit new for me, I don't have an extender board so will have to work on the loop1 board cold, I do have the full circuit diagram to help me so will give it a go.
Sackville..
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Old 25th Jun 2020, 6:07 am   #4
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Default Re: Japan Radio Company Receiver NRD-525G

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
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Old 25th Jun 2020, 8:46 pm   #5
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Default Re: Japan Radio Company Receiver NRD-525G

My thanks to you Radio Wrangler and to you Jon G4MDC, The problem was indeed in the VCO 1 circuit on the Loop 1 unit, It was caused by CV1 a small trimmer capacitor at the front end, I couldn't find any evidence of the adhesive on the trimmer but it was very intermittent, I've fitted a replacement and now the receiver is back to normal.
Thanks again for your help it is much appreciated.
Sackville...
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Old 25th Jun 2020, 10:54 pm   #6
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Default Re: Japan Radio Company Receiver NRD-525G

You've been lucky. If you'd had an Icom, you'd still be picking the much out.

David
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Old 26th Jun 2020, 9:13 am   #7
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Default Re: Japan Radio Company Receiver NRD-525G

Good to hear you have fixed it + agree David - and looking for dry joints!
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