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Help with no SSB TX #ssb


Brutus Laurentius
 

Howdy y'all!

I got my ubitx v4 a while ago.  Finally wired it up, fired it up, put on the Nextion display and firmware and it all worked out of the box! What a slick gizmo.  (And kudos to the folks who built it!)

I made a number of the mods from the ubitx.net website -- e.g. replaced the relays with axicoms and L5/L7 with SMT.  (http://ubitx.net/spectral-purity/)

I also changed the driver transistors and some of the resistors and one cap as specified there to help with evening-up the output levels:

  1. Replace the 2N3904 transistors in driver stages (Q911, Q912, Q92, Q93, Q96, Q97) with 2n2222 transistors (in a TO18 metal can)
  2. Parallel up R941, R911, R96, and R942 to get 11 ohms each by placing a 22 ohm resistor across each existing resistor.    These resistors can easily be stacked if you use 1206 surface mount parts.
  3. Replace Q90 with a BFR106 transistor.
  4. Increase R81 to between 2K and 2.7K
  5. Change C81 to 470 pF  (turns out that didn't need changed)

    Okay ... having done all that, (and before doing the mod where I use 4 different pots for per-band level adjustment) I have CW out on all bands ... but no SSB.

    I am guessing that, theoretically, if I have CW out, none of the mods went awry, and that I managed to break something else while maybe handling the board.

    TP 20 gives me a good audio waveform on a scope when I key the mic and speak into it, so the mic and amp for it are okay.   I worked through some of the test points in the troubleshooting document (e.g. q20, q22 etc.) I also have a 4 Mhz signal showing on TP 17.

    Any advice on where to look next?

    Thank you!


Evan Hand
 

There are more knowledgeable people on this board than me, so you might want to wait for their advise.  Until then, here goes with what I see at this point:

First off, there is one mod that you listed that does not impact CW transmit.  That is the L5/L7 replacement.  I would start at that point.  If you are still receiving (you did not mention how it is working on receive), then that would indicate the mod worked. If you still have the wound toroids, then you might want to try putting them back in.

Second point is that the signal at TP17 should be around 12 Mhz.  Verify that your BFO is around 11.996 Mhz. That can be measured at TP18.  Again, if the receiver is working as before the mods, then I would say the 4 Mhz at TP17 is a measurement error.  I do not see how that could show up there.

You can also check for the approximately 33 or 57 Mhz LO from Clock#1, depending on dial and USB/LSB setting at TP15.  This is used to generate the 45 Mhz IF signal. 

We do know that Clock#2 works, as that is the only local oscillator that is used in CW transmit.

Hope this helps.

73
Evan
AC9TU
 


Brutus Laurentius
 

Hi Evan ... thank you!

More info ...

Okay -- it receives just fine.  So that means L5/L7 are okay.   I see audio at TP20,  the signal at TP17 decreases in amplitude when I speak into the mic (using the stock mic) and the signal at TP16 increases in amplitude when I speak into the mic.  Instead of using my bitscope, I broke out my frequency counter and the frequency at TP18 is 11.997 (that's as accurate as that meter gets) and the scope shows it to be steady no matter what.

So I have receive, full power transmit on CW, no power out on SSB.

I'll continue tracing through the circuit, but wonder if this gives people who are more familiar with the circuit than I am a flash of insight ...  (*grin*)


Evan Hand
 

Since the receiver is working, I would now look to see if you damaged something around C20 when you did the L5/L7 mod.  Not sure what test equipment you have, but a signal injected at TP14 should show up at the base of Q20.  I would do this with the rig power removed. I would also closely inspect the sections that you scraped off the coating to solder the inductors to.  You may have damaged the trace and now have an open circuit to C20 and the transmitter IF amp.

I do not understand what you mean when you say the signal decreases at TP17 and then increases at TP16.  I am travling for work this week, so cannot get to my rig to see what the signals should look like at TP16 and TP17.  Maybe someone else can help, otherwise I will check on Friday.

73
Evan
AC9TU


Brutus Laurentius
 

I injected a ~13mhz signal at TP14 with the power off, and it showed up at the base of Q20 just fine, and looked like the original.  (13Mhz happened to be what my signal generator was set at, no special reason for that freq.)

What  mean about TP16 is that, when I I push PTT and don't speak, it is a steady waveform but when I speak, it shows changes in amplitude along the waveform, as if a carrier has been modulated.  TP17 shows a steady carrier until I speak, and then it has a similar type of response, only the amplitude decreases in response to speech.   I hope that makes sense!


Brutus Laurentius
 

Not sure how to edit -- I re-checked and TP17 doesn't show what I described.  I am, however, able to trace a modulated signal to TP 14 and to the base of Q20 ... but there isn't one at TP13 or TP1.

So I think I'm getting somewhere ... the modulated signal is present on the base of Q20 ... but NOT at the base of Q21.   Until I hit PTT, there is a signal there, but when I hit PTT, it disappears ...

 


Brutus Laurentius
 

So I did DC measurements on Q20, Q21 and Q22 and they are as expected, indicate things are connected as the should be and none of the resistors are bad:

Q20 B 2.35
Q20 E 1.6
Q20 C 7.54

Q21 B 7.54
Q21 E 6.85
Q21 C 11.55

Q22 B 6.86
Q22 E 6.1
Q22 C 11.54

With PTT pressed, I have a sinusoidal signal present at the base of Q20, but not at the collector of Q20 or the bases of Q21/Q22.  

It sure doesn't seem terribly likely ... I mean, when is the last time a transistor of that sort actually failed?  And if a transistor fails, would it still give you the expected ~.6V difference between B & E?

But that's what it seems like to me.   I DO have some SMT 3904s and hot air so it wouldn't be terribly onerous to change those three transistors.  

Any thoughts?

 

 


Brutus Laurentius
 

Changed out the three transistors ... nothing changed.  Signal on base of Q20 ... but not on the collector.

(scratches head)


 

I would check C21 and R23, if either are open then no gain! DC voltages will be correct.

Raj


At 07-02-19, you wrote:

So I did DC measurements on Q20, Q21 and Q22 and they are as expected, indicate things are connected as the should be and none of the resistors are bad:

Q20 B 2.35
Q20 E 1.6
Q20 C 7.54

Q21 B 7.54
Q21 E 6.85
Q21 C 11.55

Q22 B 6.86
Q22 E 6.1
Q22 C 11.54

With PTT pressed, I have a sinusoidal signal present at the base of Q20, but not at the collector of Q20 or the bases of Q21/Q22. 

It sure doesn't seem terribly likely ... I mean, when is the last time a transistor of that sort actually failed?  And if a transistor fails, would it still give you the expected ~.6V difference between B & E?

But that's what it seems like to me.   I DO have some SMT 3904s and hot air so it wouldn't be terribly onerous to change those three transistors. 

Any thoughts?

 

 


Brutus Laurentius
 

Thank you, Raj ... tested C21 and R23 and both are good ...


Brutus Laurentius
 

Something I hadn't thought to do -- I looked at TP14 with CW and with SSB, and the signal with CW is dramatically larger -- so there's a problem before that.  (I had no idea how big the signals should be.)


 

Burtus,

CW originates from CLK#2 and is not connected to TP14. So whatever you see is not a problem.
We have to look elsewhere.

Raj

At 07-02-19, you wrote:
Something I hadn't thought to do -- I looked at TP14 with CW and with SSB, and the signal with CW is dramatically larger -- so there's a problem before that. (I had no idea how big the signals should be.)


Brutus Laurentius
 

Thank you! With persistence it will yield!


Evan Hand
 

Just on a thought, you may want to check the clock#1 signal and verify that when you press the PTT it is either approx. 33 or 57 MHz depending on side band.  Also verify the signal you are seeing at the base of Q20 with PTT pressed is around 45 Mhz.  At a loss to explain why no signal at collector of Q20. 

You are using high impeadance probes?

73
Evan
AC9TU


 

Brutus,

Your RX is fine so the mixers are ok, the xtal filter and the 45Mhz filter is fine.
The only issue is in the TX side of the BiDi amps. If the dc voltages are fine then
you have a bad coupling cap or 47 Ohm resistor.

Raj

At 07-02-19, you wrote:

I injected a ~13mhz signal at TP14 with the power off, and it showed up at the base of Q20 just fine, and looked like the original. (13Mhz happened to be what my signal generator was set at, no special reason for that freq.)

What mean about TP16 is that, when I I push PTT and don't speak, it is a steady waveform but when I speak, it shows changes in amplitude along the waveform, as if a carrier has been modulated. TP17 shows a steady carrier until I speak, and then it has a similar type of response, only the amplitude decreases in response to speech. I hope that makes sense!


Evan Hand
 

Clock#1 and clock#0 are turned off for CW transmit. Clock#2 is adjusted to the transmit frequency (with the cw tone offset) when the CW is keyed. 

73
Evan
AC9TU


 

Take a pic and share of your L5/7 area.

Raj

At 07-02-19, you wrote:
Thank you! With persistence it will yield!


Brutus Laurentius
 

Here's a pic of that area! :)


Brutus Laurentius
 

Hi Evan,

clock 1 seems to be about 33 Mhz and clock 2 about 50.49 ?   I'm using high impedance probes


Evan Hand
 

what is the frequency that is set on the display and what mode - USB/LSB?  Measure Clock#2 when in receive and then in transmit.  Should stay the same for SSB.

73
Evan
AC9TU