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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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13th Apr 2020, 5:08 pm | #1 |
Triode
Join Date: Jun 2018
Location: Ash, Surrey, UK.
Posts: 38
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PLL Problem With Yaesu FRG-7700
Hi All, My ageing FRG-7700 which has been fine for many years suddenly started playing up. I use it for (amongst other things), for listening to broadcast radio. I was listening to radio 4 today when it suddenly lost frequency and the frequency display went from 198KHz to around 700KHz but the frequency was not locked, i'm guessing this is something to do with the PLL but wonder if anyone has had a similar issue? It will be a shame to to lose it after all this time but my knowledge of PLL circuits are limited to say the least. Any input would be gratefully received. Many Thanks.
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13th Apr 2020, 5:22 pm | #2 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,864
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Re: PLL Problem With Yaesu FRG-7700
Japanese radios of that era had a problem with trimmer capacitors in the VCO areas getting corroded away by the brown goop they used to try to combat microphony. Try a visual inspection of the different VCOs as a first move.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
14th Apr 2020, 12:34 am | #3 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
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Re: PLL Problem With Yaesu FRG-7700
A receiver of this age will benefit from some basic maintenance, e.g. cleaning switches
and controls. The problem could be as simple as the VFO capacitor rotor contacts need a clean and lubrication. This could be be confirmed if you have the memory unit (option) fitted, and the frequency entered does not drift off. Worth checking that the MR switch contacts may need a clean if they never have been. |
14th Apr 2020, 8:11 am | #4 |
Triode
Join Date: Jun 2018
Location: Ash, Surrey, UK.
Posts: 38
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Re: PLL Problem With Yaesu FRG-7700
Thank you both for your replies, I’ll have a look at these areas mentioned and see if anything is apparent. This does not have the memory option but pressing the MR switch does switch it to around 6.85MHz which is stable. Releasing the MR switch, it then reverts to the unlocked state. Unfortunately I don’t have either a scope or frequency counter for calibration, just my trusty Fluke DMM for checking voltages.
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14th Apr 2020, 10:47 am | #5 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,864
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Re: PLL Problem With Yaesu FRG-7700
You're definitely heading into scope and counter territory. The logical path is to fix this oversight, then fix the frog7700.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
14th Apr 2020, 10:52 am | #6 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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Re: PLL Problem With Yaesu FRG-7700
There are 4 bands to deal with in an FRG7700 PLL.
0-5MHz, 6-12MHz,13-20MHz and 21-29MHz. Is it the same on all of the MHz segments or only on the bottom one 0-1MHz as you have already described? Please check the behaviour on each MHz segment across the range as what happens will give valuable clues. Last edited by Jon_G4MDC; 14th Apr 2020 at 10:59 am. |