Galaxy Saturn weak SSB receive...

[Hawkeye351]

What's up guys....

Got another Saturn on the desk.

Issues:
Low transmit in all modes.
Fixed, was the last final in the stage. Replaced, touched up bias and retuned output stage. Transmit now works great in all modes.

Weak SSB receive in both LSB and USB. The AM receive is great. Realigned receive (AM and SSB), AM turned out awesome, SSB still weak. Have to turn volume up over halfway, and the signals on SSB are down also. Again, AM is great, volume at about 9 o'clock is plenty loud.

Replaced C31, C32, C190, C193, C19, C20.

Checked C43 and C89.
C43 is marked as a 18pf and tests close to that.
C89 is marked as a 15pf and tests close to that.

Checked voltages on all ICs:
All ICs check out close to what they should be.

Checked all SSB tranny's in the chain for receive:
TR12
TR14
TR15
TR17
TR19
TR20
TR21
TR22
TR31
TR36
TR37
TR38
TR40
TR41
TR42

Cleaned the mode control.
Tested RF Gain control, no issues, AM receive is great and RF gain functions as it should.

The only problem I can think of is TR22, The 4th SSB IF amp.
It shows very high voltage on all pins, and nowhere near close to specs.

Are there any other electrolytic caps in the chain that supplies TR22 with it's voltage that could cause it to show very high voltages on all the pins? I noticed TR21 feeds it, but TR21 voltage is correct.

Thank you guys for all your previous help.

 

[nomadradio]

Hmm. TR21 emitter connects to TR22 base.

Don't see how voltages on TR21 could be right if they're wrong on TR22, since they connect directly together?

If TR20 has the correct approx 6/10 of a Volt on the base lead, this makes it sound as if TR20 is lazy, not pulling current away from the base of TR21.

This 3-transistor circuit uses negative feedback to keep the DC voltages stable. If TR22 voltages are high, either the feedback to the base of TR20 is wrong, or it's not handling the feedback correctly.

73

 

[Hawkeye351]

I see D84 in the same chain. I wonder if this diode could cause SSB receive volume to be weak but AM receive is great, and xmit in all modes to be fine.

Not sure if this means anything, but AM xmit is around 30w peak and SSB xmit is around 22w to 25w (in that area).

Nomad, I've been scouring around through this sites forum on similar issues on other radios with this same board number and noticed you mentioned in those posts about the SSB crystal filter and how to check it with this type of issue. Could this be my problem? And if so, which one is it (fl3, fl2)? Also, could you provide a simple method on testing the proper functionality of this filter?

I did notice TR52 and C190 get extremely hot within seconds of switching to SSB, not transmitting, just receiving. Although I replaced C190 and checked voltages on TR52, they still get extremely hot within seconds of just switching to SSB in receive.

It acts as though the SSB sensitivity is almost non existent, only strong SSB signals come through. Still have to turn volume up quite a bit though. But AM/FM is great, sensitivity is great, volume is plenty at 9 o'clock.

All oscillators lined up perfectly with no problems.

This SSB chain seems to be a simple circuit, but confused at what's the problem.

By the way, the SSB strong signals that do make it through the circuit, sound watery on receive. And if a strong local operator keys up on the same SSB mode and frequency, then it takes around 1.5 seconds for the receiver to recover.

 

[Hawkeye351]

Ok, done some proding around L13 and L14 with a small metal shaft screw driver with my finger touching the shaft of the screwdriver.

The only spot that the receive on sideband improves to normal, is the unused pin (on the 3 pin side) and the outer pin (on the 2 pin side) of L13.

Replaced C89 with a new cap of same type and value, no change in SSB receive. Tried different values (up and down in value), with no improvement.

Did the same to C43, no change in receive on SSB.

The only thing that brought the SSB receive up to normal, sounded normal and S-Meter movement improved on SSB was touching those 2 places on L13. Receive sounded awesome by touching either of those 2 legs on L13 with a metal screwdriver with my finger touching the shaft of the screwdriver.

 

[Hawkeye351]

Did voltage checks again on the following transistors:
TR12, TR14, TR19, TR20, TR21, TR22, TR30, TR31, TR52. All checked in LSB mode.

The results are as follows:

TR12
B - 0.65
C - 0
E - 0

TR14
B - 0.69
C - 0
E - 0

TR19
B - 1.67
C - 6.65
E - 0.03
Hmmm, emitter should be 0.80v, not 0.03v.

TR20
B - 0.68
C - 3.23
E - 0

TR21
B - 2.52
C - 6.17
E - 3.13
Hmmm...seems backwards from what it should be. Voltage chart shows the base of TR21 and the base of TR22 tied together

TR22
B - 2.52
C - 7.46
E - 1.83
Wow, it's high... And yes I did double check the BCE orientation. Chart shows the base of TR21 and TR22 tied together.

TR30
B - 3.07
C - 6.31
E - 2.48

TR31
B - 0
C - 2.95
E - 0
Hmmm, base should be 0.70v, not 0v.

TR52
B - 6.84
C - 13.00
E - 7.36

Weird voltages on a few. How is it possible that the collector of TR22 is over 7v when it's being directly fed by the emitter of TR21 which is slightly over 3v? This makes no sense... Still, the collector of TR22 is way too high at 7.46v when it should be 2.90v. The emitter of TR22 suppose to be 7.40v, not 1.83v. The base of TR22 suppose to be 0v, not 2.52.

 

[Hawkeye351]

This is the voltage chart I used. For a 99v, but basically the same board and layout.

 

[Hawkeye351]

Hmmm, that's not right, but I'm not sure if this would affect SSB receive. What I found is that C133 is in backwards. I verified with a parts layout pic, a 99V I have sitting aside waiting for me to install new lights, an 11B which is one of my personal radios, another Galaxy Saturn which is also my personal radio and another Saturn that's waiting for me to install new adders.

I'll swap it around tomorrow. I hope it didn't cause any damage in other places. This is a Chinese cap, not the nichicons that I always use.

 

[Hawkeye351]

After looking over schematic more on the routes of C133, yes it will affect SSB receive. From the looks of the schematic, it seems as though C133 is the AMC timing capacitor or some type of smoothing cap. Just curious as to how the radio modulated on transmit with this one in backwards, but it did.

Oh well, I'll swap it out in the morning, my eyes are tired.

 

[nomadradio]

touching those 2 places on L13.

Should have asked about the position of the tuning slug in L13 and L14. When you touched one end of the primary winding you added capacitance. If that brings up the signal, it tells us that L13 is tuned to some frequency above where it should be.

Makes it sound as if the tuning slug on L13 is dead flush with the rim of the hole.

This happens when the coil's built-in capacitor fails. That "dead flush" position is where the coil's inductance is maxed. Makes it look like a peak, but it's not. It's the coil getting close to resonant, and then farther away as the slug rises above the rim of the hole.

Adding back the missing capacitance is easier than replacing the whole IF transformer. The schematic shows the internal capacitor across the primary winding, but doesn't reveal its capacitance value. We keep a bag of 30pf trimmer caps handy on the bench for this purpose, like the one in the pic. Goes across the two outer pins of the 3-pin side.

Might take more than 30pf for L13, don't have a bench note on that. If you try this, and the trimmer goes to full capacitance without getting a peak, then it needs more capacitance.

I normally back the slug two turns down below the rim before trying to peak the trimmer cap.

Kinda like "Tune and Load", might be some back-and-forth between the tuning slug and the trimmer cap to get a proper resonant peak.

73

 

[Hawkeye351]

None of these slugs are flush for a peak. All IF can slugs in this radio are all about 2 to 3 turns down from the top, thats where they peak.

I think I found the issue though. C133 is in backwards. And according to the schematic, C133 will have an affect on L14, which in turn will affect TR22 also. That's probably why the receive came up when I touched those 2 pins of L13 with a metal screwdriver earlier. Although C133 may be in the AMC circuit, it still has a route straight to L14, L12, L52 and other SSB receive spots. Weird how it's laid out, but I think this may be the problem.

I confirmed the orientation of C133 was wrong by the silkscreen on the board and looking over a few other radios I have around here that have the same board, and by looking over the parts layout diagram.

Sorry to bother you earlier....
Thank you nomad.

 

[Hawkeye351]

Outcome after switching C133 around the right way:
Slightly better SSB receive.

Realigned entire radio again after switching C133 around the right way:
Slightly better than above.

Swapped out TR22, still same high voltages, no difference in receive as from the above improvements.

I did notice that if I flip the NB on
while in either sideband that the SSB receive comes up even more, turn NB off and ssb receive drops a little. NB works as it should in AM. It's as though the NB is working backwards in SSB as compared to AM.

Also, I noticed if I switch between LSB and USB while someone is talking, the tone stays the same and you can tune them in just fine. It's as though LSB and USB are about the same. Whoever I hear on either sideband, I can hear them also on the other sideband by just using the clarifier slightly.

Also, TR52 still gets scorching hot within seconds of being on either sideband just listening.

All cores in all the IF cans peak at 2 to 3 turns down from the top, none are flushing with top of can or bottoming out.

SSB output swing improved from previous 25w, now it's 30w (same as AM swing now), after switching C133 around the right way.

Already tested it on air on SSB barefoot, talked to many places, didn't even have to touch fine or course tune at all, both stayed straight up 12 o'clock the entire time.

Comparison:
AM receive while hooked to antron:
5 to 7 s-units of skip.
SSB receive while hooked to antron:
1 to 4 s-units of skip at times, not noisy at all.

Volume on AM for comfortable listening is around 9 o'clock.
Volume on SSB for comfortable listening is around 10 o'clock.

 

[Hawkeye351]

Replaced FL3, replaced TR12 and TR14, checked D70, D28, D25 and a few other diodes in the L13/L14 area. Still AM receive is better than SSB.

I removed a 25pf NPO cap I had soldered on the outer 2 pins of L13 and now the sidebands don't run into each other as before.

I also got the NB working properly now.

Comparing SSB receive to my FT-950 which is connected to an HF wire (G5RV Jr), the 950 is showing around 5 s-units on SSB, whereas the Saturn shows around 4 s-units. Guess that's as good as this one is gonna get.

 

[Hawkeye351]

This Saturn has truly gotten the best of me.

Replaced D11, D15, D16, D24, D25, FL3, C31, C32, C43, C67, C89, C90, C95, C190, C193, C35, C40, C19, C20, C333, C133, TR12, TR14, TR22, TR20, TR21, TR17, TR18, TR52, TR49, L13, L14...

Checked every component in the sideband chain (by following the 99V block diagram).

Checked ALL transistors again (TR22 still high), checked ALL IC's again, checked all other diodes...


Realigned radio and receive again...

Still SSB isn't as good as AM or FM. Slightly better but not quite right.

Has to be the mode knob, but don't know how to test it.

Giving up on this one. Sidebands are slightly better than when I started. AM and FM is awesome on receive.