This thing has had a full alignment works absolutely fantastic tx/rx spot on. But it does have one issue on ssb ? At full rf gain the audio has some distortion on it, back the rf gain down to six it clears right up spot on frequency. I've read some other post about this issue checked c43 10pf and c89 15pf per schematic lowered c89 to 5pf it shifted the frequencies down. checked voltages on agc circuit transistor 19-24 there good haven't pulled and tested them yet. L8 is just up about 3/4 of a turn from the bottom. I don't have have 10.240 on pin three of IC5 and I have voltage present on pins 4,5,6 (chip possibly)? I used the galaxy 99v for the alignment everything went well. Just looking for some experience and direction with this problem before I start pulling individual parts and testing. Thanks Ira
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Eagle 2000 ept360014b
- Thread starter ira parker
- Start date
P.S. I swapped out fl3 ssb filter with a known good one just because I wanted to eliminate it as a possible cause of swamping the agc.
hold everything....
the SSB receive signal in this design takes a different
path at the end. there is extra gain and transformers to tune (L13 and L14).
and AGC is separate at the end.
there is not enough carrier injection from the transistor TR30
carrier oscillator to the SSB receiver detector.
add more RF by increasing capacitor C73 to 47 to 82 pico-F.
just take a 47 pico-F capacitor and solder it under C73.
I recently replaces C73 with a 100 pico-F cap and it works
on an old 2970 0013 board.
the SSB receive signal in this design takes a different
path at the end. there is extra gain and transformers to tune (L13 and L14).
and AGC is separate at the end.
there is not enough carrier injection from the transistor TR30
carrier oscillator to the SSB receiver detector.
add more RF by increasing capacitor C73 to 47 to 82 pico-F.
just take a 47 pico-F capacitor and solder it under C73.
I recently replaces C73 with a 100 pico-F cap and it works
on an old 2970 0013 board.
Thanks Bayou, I will give it a shot in the mourning and test tr30 while I'm at it. I did test the voltages on it tr31 and tr15 also they were all good. I was thinking agc but the oscillator makes sense . Appreciate the help I'll post up the results once again Thanks Ira
transistor TR30 should be good. don't mess with it.
TX in SSB and AM is working.
you can see that the AGC is working. the S-meter is moving
is a good indication of that, and it works in AM receive.
TX in SSB and AM is working.
you can see that the AGC is working. the S-meter is moving
is a good indication of that, and it works in AM receive.
comparing the 2 schematics complete different locations 2970 schematic is just past the ssb filter, on the 14b schematic it is just before the product detector?
Replaced c73 (14b schematic) with 100pf no change, will swap it back for the stock one which is 18pf and test good. going to pull tr15 and test it and associated parts.
just got home from a long day at work.
yes C73 on the 14B board, going to the product detector.
for TP6
I added more RF osc signal on this older 2970 with a
013 board and the cap is C90.
I could see on the scope that the carrier level was low,
so put in a 100 pico-F and strong SSB signals are good.
yes C73 on the 14B board, going to the product detector.
for TP6
I added more RF osc signal on this older 2970 with a
013 board and the cap is C90.
I could see on the scope that the carrier level was low,
so put in a 100 pico-F and strong SSB signals are good.
Do all SSB signals distort, or is it just the strong ones?
The RF gain only controls the bias of the first RX preamp (TR17). The AGC controls the attenuation of the signal that makes it to the preamp (via D15 and D16) and also controls the gain of the first SSB mixer (TR19) and the second AM mixer (TR8) by controlling their bias points.
Having the AGC control the gain of multiple stages is what gives the radio the dynamic range needed to handle the wide range of RX signal levels coming in without overloading the IF stages or having a significant impact on audio volume.
If turning the RF gain down makes the distortion go away, I am inclined to believe that weak signals would come through fine, and to me, this would move my focus from the detector to the AGC chain.
There is a voltage chart for IC1 (half of which is used in the AGC line) in the galazy saturn service manual. I am not sure how much help it will be with varying signal levels coming in, but on a dummy load, they may help narrow down the issue.
Regarding your first post, if the frequency alignment went good, IC5, the PLL, should be ok. No signal on pin 3 is likely the probe loading down the oscillator. Pin 4 is a buffered copy of pin 3, use that to look at the 10.24MHz signal. It will be a square wave, but it tells you that much is working ok. Pin 5 is pin 4 divided by 2 (5.12MHz). Pin 6 is the frequency select and controls the reference divider. if the frequency alignment went ok, don't mess around with the PLL.
*Someone* should redraw that AGC path and the detector circuit in a way that makes it easier on the eyes (and brain).
The RF gain only controls the bias of the first RX preamp (TR17). The AGC controls the attenuation of the signal that makes it to the preamp (via D15 and D16) and also controls the gain of the first SSB mixer (TR19) and the second AM mixer (TR8) by controlling their bias points.
Having the AGC control the gain of multiple stages is what gives the radio the dynamic range needed to handle the wide range of RX signal levels coming in without overloading the IF stages or having a significant impact on audio volume.
If turning the RF gain down makes the distortion go away, I am inclined to believe that weak signals would come through fine, and to me, this would move my focus from the detector to the AGC chain.
There is a voltage chart for IC1 (half of which is used in the AGC line) in the galazy saturn service manual. I am not sure how much help it will be with varying signal levels coming in, but on a dummy load, they may help narrow down the issue.
Regarding your first post, if the frequency alignment went good, IC5, the PLL, should be ok. No signal on pin 3 is likely the probe loading down the oscillator. Pin 4 is a buffered copy of pin 3, use that to look at the 10.24MHz signal. It will be a square wave, but it tells you that much is working ok. Pin 5 is pin 4 divided by 2 (5.12MHz). Pin 6 is the frequency select and controls the reference divider. if the frequency alignment went ok, don't mess around with the PLL.
*Someone* should redraw that AGC path and the detector circuit in a way that makes it easier on the eyes (and brain).
brandon7861 says - - "*Someone* should redraw that AGC path and the detector circuit in a way that makes it easier on the eyes (and brain)."
yes! much agreed. it is hard to see clearly on the schematic.
but on the old 2970 I successfully got working on strong SSB signals.
I found, I think, there is an extra gain stage for SSB receive,
and the SSB AGC has a slightly different path.
the S-meter would read higher for the same signal level in
SSB over AM. on the 014B board, that would be from L13 to L14.
I think I read posts about them newer 5555 and 6666 radios
having distortion in SSB receive with strong signals.
same problem. maybe. It is about the same circuit.
We will all figure it all out.
,,
yes! much agreed. it is hard to see clearly on the schematic.
but on the old 2970 I successfully got working on strong SSB signals.
I found, I think, there is an extra gain stage for SSB receive,
and the SSB AGC has a slightly different path.
the S-meter would read higher for the same signal level in
SSB over AM. on the 014B board, that would be from L13 to L14.
I think I read posts about them newer 5555 and 6666 radios
having distortion in SSB receive with strong signals.
same problem. maybe. It is about the same circuit.
We will all figure it all out.
,,
Is the problem you and ira are describing common to all these radios, or is this problem unique to just the radio ira has? Are we troubleshooting a circuit problem that just started, or a circuit design flaw that was always there? If it is a design flaw, we can look at what that ciruit evolved to.
99v/saturn next to the 2547 circuit:
The components in red moved below the green capacitor, and that cap in green was made much bigger. There are a few other chenges, like C73(C79 in the 2547) and C72(C74) too. Maybe duplicating these changes would help.
Edit: If one were to attempt to make these changes, don't forget the NB line that would have to go to the cathode of D26 so C36(C78) don't block its function.
Last edited:
Yes the weaker signals (s-4) and below are fine anything above that can be cleared up by reducing rf gain back to 5 or 6 depending on incoming signal strength. Have qso'ed with a local that has a icom 7300 and the radio is centered on his spectrum graph. Am receive is normal haven't checked fm. I've been in a lot of these galaxy boards this is the first time coming across this issue! I'm with you on the agc circuit because it does sound like it's swamping the front end (kinda like when someone is transmitting real close) fuzzy with a little distortion. I will get into that in the mourning. I've checked voltages on tr 12,15,17,19-22, 30 volts are fine. Pulled tr15 (ssb detector) and tested it, was a little low on hfe so I replaced it, the 2 electrolytic were a little high so I replaced them also tested all 3 polyester caps (I've had a few go bad in the audio chain before) there all good. Sure do appreciate the input on this had me scratching my head today I'll post what I find on the agc . Once again thanks for all the help guys. Ira
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