PLL Problem With Yaesu FRG-7700 - UK Vintage Radio Repair and Restoration Discussion Forum

ChasHeater · 13th Apr 2020, 5:08 pm

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.

Radio Wrangler · 13th Apr 2020, 5:22 pm

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

Restoration73 · 14th Apr 2020, 12:34 am

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.

ChasHeater · 14th Apr 2020, 8:11 am

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.

Radio Wrangler · 14th Apr 2020, 10:47 am

You're definitely heading into scope and counter territory. The logical path is to fix this oversight, then fix the frog7700.

David

Jon_G4MDC · 14th Apr 2020, 10:52 am

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.

13th Apr 2020, 5:08 pm	#1
ChasHeater Triode Join Date: Jun 2018 Location: Ash, Surrey, UK. Posts: 38	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.

13th Apr 2020, 5:22 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	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 __________________ 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
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	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
ChasHeater Triode Join Date: Jun 2018 Location: Ash, Surrey, UK. Posts: 38	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.

14th Apr 2020, 10:47 am	#5
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	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 __________________ 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
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	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.