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  1. Yaesu-FT-980
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Untunable SSB, CW. but AM is OK

 

By fiddling with the I.F. width control I can "almost" resolve speeech on SSB but clearly something is wrong, with my money on a drifted oscillator.

I did check the Master Oscillator (30 MHz) and this was slightly low so I corrected this. I then checked the tripler output for 90MHz and it wasn't there - but 30 MHz was!

I thought maybe the 30MHz was bleeding through a weak 90 MHz but cant check this at the mo. as my 100MHz scope has packed up.

I read Mat's description of his similar fault and cure but was not sure of the location/part number of the trimmer cap he mentioned and ultimately replaced. I did locate the transformer he replaced but I havn't check mine yet.

So my question is (mainly for Mat?) "Can you state where I can find that variable cap you replaced? You mention "two tin cans" and I wondered if this was in the VCO enclosure (how do you get the lid off?!!) or is it on the VFO board. Can't quite place you photo.

Kind regards

Peter G0LQU
 

Hi Peter
I had similar problems with my ft980 and replacing the trimmer capacitor you mention and worked for me its located on the VCO/PLL board part number TC4001 its a? 1-3pf its inside a metal enclosure you will have to carefully remove the lid by unsoldering the tags ether side,? a replacement trimmer is not easy to find, but I do have one here if you have trouble? getting hold of one just e-mail me my info is good on QRZ.co

Cheers Mal G0MIX?
 

Sounds like the small variable cap in the VCV.? Use a non metal adjustment tool and see if you can get the audio working.? First test LSB and compare to USB.

If there is a big differece then the VCV cap needs to be adjusted.? This was a major problem in early FT-980's.? My first was bought new in 1983 and later models have a better ceramic variable cap.? Everything else looks OK.? Good luck.

73 Dave K4JRB?

-----Original Message-----
From: <[email protected]>
Sent: Oct 7, 2022 1:35 PM
To: <[email protected]>
Subject: [Yaesu-FT-980] Untunable SSB, CW. but AM is OK

?

By fiddling with the I.F. width control I can "almost" resolve speeech on SSB but clearly something is wrong, with my money on a drifted oscillator.

I did check the Master Oscillator (30 MHz) and this was slightly low so I corrected this. I then checked the tripler output for 90MHz and it wasn't there - but 30 MHz was!

I thought maybe the 30MHz was bleeding through a weak 90 MHz but cant check this at the mo. as my 100MHz scope has packed up.

I read Mat's description of his similar fault and cure but was not sure of the location/part number of the trimmer cap he mentioned and ultimately replaced. I did locate the transformer he replaced but I havn't check mine yet.

So my question is (mainly for Mat?) "Can you state where I can find that variable cap you replaced? You mention "two tin cans" and I wondered if this was in the VCO enclosure (how do you get the lid off?!!) or is it on the VFO board. Can't quite place you photo.

Kind regards

Peter G0LQU

?
 

Hi Dave and many thanks for your (ground breaking for me!) information. Yes my FT 290 IS a very early model. G0MIX has also confirmed this with me and sent useful pics of the location of that cap.

Kind regards

Peter G0LQU

Dave Thompson wrote:


Sounds like the small variable cap in the VCV. Use a non metal adjustment tool and see if you can get the audio working. First test LSB and compare to USB.

If there is a big differece then the VCV cap needs to be adjusted. This was a major problem in early FT-980's. My first was bought new in 1983 and later models have a better ceramic variable cap. Everything else looks OK. Good luck.

73 Dave K4JRB
-----Original Message-----
From: <[email protected]>
Sent: Oct 7, 2022 1:35 PM
To: <[email protected]>
Subject: [Yaesu-FT-980] Untunable SSB, CW. but AM is OK


By fiddling with the I.F. width control I can "almost" resolve speeech on SSB but clearly something is wrong, with my money on a drifted oscillator.

I did check the Master Oscillator (30 MHz) and this was slightly low so I corrected this. I then checked the tripler output for 90MHz and it wasn't there - but 30 MHz was!

I thought maybe the 30MHz was bleeding through a weak 90 MHz but cant check this at the mo. as my 100MHz scope has packed up.

I read Mat's description of his similar fault and cure but was not sure of the location/part number of the trimmer cap he mentioned and ultimately replaced. I did locate the transformer he replaced but I havn't check mine yet.

So my question is (mainly for Mat?) "Can you state where I can find that variable cap you replaced? You mention "two tin cans" and I wondered if this was in the VCO enclosure (how do you get the lid off?!!) or is it on the VFO board. Can't quite place you photo.

Kind regards

Peter G0LQU
 

Thank you so much Mal for that information and the pictures.and the offer of a variable Cap if I need one. I've just managed to get off the main metal lid of the VCO/PLL unit and am now confronted by that little metal box you mentioned. I may try to adjust the cap through the holes in the box, although the alignment is not great for accessing the adjusting screw head! One hole givese access to a test point so I will look that up.and see if I can measure anything at that point.

My "solder sucker" iron is not strong enough to tackle the metal lid solder so not sure how to proceed yet with that.

Kind regards

Peter G0LQU
 

Can you hear CW? If CW/SSB both do not work, but both AM/FM do then it lends itself to a BFO path problem (oscillators, amp, or mixer). You can check FM station by switching to GEN mode and listening into a maritime mobile or broadcast segment.

There is a good oscillator block diagram on page 49 of the FT-980 Technical Supplement ... but I usually use the big block diagram as the oscillator one over-simplifies things.

--
-Mat Breton, N8TW
 
Edited

You can check if the BFO oscillator (the one in the tin can) is working by checking the DC voltage on test point TP4004, which is actually located outside of the tin can (not the one inside). The test and adjustment procedure is located on page 23 of the Technical Supplement. It takes a very steady hand and good tools to adjust the stock trimmer (peak the voltage on TP4004).

Note that the exact voltage levels can vary rig-to-rig, but you should see 2-7 volts at all times, and there should be a 3v or so movement as you sweep the width knob.

--
-Mat Breton, N8TW
 

Thanks for your posts Mat - very useful. I can "hear" SSB and CW but very muffled and indistinct. I did check the master oscillator (30MHz) and this was a few KHz low so that was corrected. But I couldn't find the 90MHz signal after the tripler! Maybe I should check these oscillators then proceed to the BFO.

Very grateful foir your help Mat

Peter G0LQU

Mat Breton N8TW wrote:


[Edited Message Follows]

You can check if the BFO oscillator (the one in the tin can) is working by checking the DC voltage on test point TP4004, which is actually located outside of the tin can (not the one inside). The test and adjustment procedure is located on page 23 of the Technical Supplement. It takes a very steady hand and good tools to adjust the stock trimmer (peak the voltage on TP4004).

Note that the exact voltage levels can vary rig-to-rig, but you should see 2-7 volts at all times, and there should be a 3v or so movement as you sweep the width knob.

--
-Mat Breton, N8TW
 

I seem to recall the voltage should be 6.3v on both Upper and lower SSB.? This may have come from a 1983 FOX Tango newsletter but it may also be in the FT980 tech supplement.? If you don't have the tech supplement I suggest you get one.? Has alignment procedures and a whole set of schematics.? They sell on RBAY often.

Dave K4JRB

-----Original Message-----
From: <[email protected]>
Sent: Oct 9, 2022 8:25 PM
To: <[email protected]>
Subject: Re: [Yaesu-FT-980] Untunable SSB, CW. but AM is OK

?

[Edited Message Follows]

You can check if the BFO oscillator (the one in the tin can) is working by checking the DC voltage on test point TP4004, which is actually located outside of the tin can (not the one inside). The test and adjustment procedure is located on page 23 of the Technical Supplement. It takes a very steady hand and good tools to adjust the stock trimmer (peak the voltage on TP4004).

Note that the exact voltage levels can vary rig-to-rig, but you should see 2-7 volts at all times, and there should be a 3v or so movement as you sweep the width knob.

--
-Mat Breton, N8TW

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