FT-102 low volume on SSB and CW but ok on Am

[KD8HLV]

With the AGC on I have to run the volume all the way up to listen to SSB and CW  but in AM mode it has plenty of volume with the AGC on.   if I turn the AGC off it has tons of volume and is distorted  on the strong signals.     Looks like there is quite a few FT-102 owners on here, has anyone out there ran into this before? 

Thanks


Doug KD8HLV

[KU8L]

Hi Doug:

This may be a carrier set-point issue.  ie..signal not positioned in frequency relative to the filter passband.  Becomes non-critical for AM.  With the AGC wide open, it is loud enough but the offset still causes the distortion. 

Do you have a counter?  That can typically get you very close.

Curt

[KD8HLV]

Hi Curt,

I do have a counter and can check the carrier point ,  The radio works and sounds very good with the agc on, it just isnt loud enough even at full volume.   with the agc off at full volume its distorted because its cranked up way too far. backing the volume control and the rf gain down makes it nice and clear but then the audio out of the speaker is about equal in loudness to when the agc is on.     wouldnt the carrier offset make it distorted with and without the agc on ?

Have you done anything more with the Apache lately?

Doug

[KU8L]

Hi Doug:

It might do as you suggest, but the carrier offset might just cause a low level problem.  Then, when the AGC tries to make it up, causes the distortion.  One way to tell, perhaps, is to try it on LSB USP to see if there is any difference.  Also, I guess, it would show up in Tx as well but kind of depends on the architecture. 

I think we talked about what is different about the way the AGC works in SSB/CW Vs AM.  The big difference right away is that the AGC input signal in AM comes from the AM detector and the SSB/CW AGC comes from the product detector--this might give another clue as to where the issue is. 

I'll see if I can find a 102 block diagram/schematic and give you a little better idea.

Apache is running well.  I am still running outboard audio but will eventually put it back internally.  I think the way to go now is to open up the bandpass filter somewhat, improve the response thru the audio sections, and then make a controllable clipping set-up with workable level controls instead of the inside the box adjustments.

Will soon be starting the work on the BTA but Apache will remain on the vintage desk.

Curt

[KU8L]

Hi Doug:

Just looking at the IF freq relationship diagram in the supplement and the main block diagram in the inst manual shows that the AM detector is picked off just prior to the last Mixer that feeds the product detector.  I would be looking at the things going on at that mixer--especially the oscillator freq there.

Its easy to double check the carrier point but if it sounds ok when monitoring on both USB and LSB, then the carrier point is close enough to not cause your issue.

Curt

[W1RKW]

Google and contact Mal Eiselman, NC4L.

[Steve - K4HX]

Or look at the schematic.

[KD8HLV]

Curt  the carrier point was right on, ran out of time, will dig back in after work tomorrow

RKW  I have talked to Mal,  I may have to ship it down to him   but I want to give it a shot first

HK  Ive been doing that   

[Steve - K4HX]

And what AGC voltages did you measure for AM and SSB?

[W1RKW]

Doug,
I think a couple of the guys here are onto something.  If you don't have the block diagram and circuit description from the manual you can download load it from here: 

http://www.radiomanual.info/schemi/FT102_user_VA3VFO.pdf

On pages 28 and 30 of the document itself (not the PDF reader) shows the block diagram and the AGC description, respectively.  If you target the components in the upper left corner of the block diagram you may find your answer to the symptom.

[KD8HLV]

RKW,  thank you   I have the service manual and owners manual    and have been talking to Malcolm in Florida,    he thinks its in the audio board . after talking to him Im sending the board down to him to test.    a second working 102 would really help in the trouble shooting department.    Film at 11    Ill let you know what I find

73