Both sides are common to ground because the trimmer is in parallel with T1 primary, which is a short circuit to DC.

You kids, I'll learn y'all yet ;-)

--
Julian, N4JO.

Bryan,

Here are the power curves for each band:



Based on your measurements, I believe it is working as designed, though maybe a little low at 20volts (36watts vs 30watts).? I would not do anything else at this time other than having fun using it.

73
Evan
AC9TU

Oh dear me no, absolutely not; that little guy is the 74ACT00 - a 5V low power logic device - and it had better not be hot. If it is, then it has failed, and that usually happens because the regulator has failed and the 5V line has gone over-voltage and destroyed it, and if that's the case, other things are dead too, like the Si5351A...

However, thinking...

An SWR of 1.4 isn't seriously wrong at all... is there any way it might have been higher at some point? A high SWR could take out one or more of the BS170 output FETs, and depending on the failure mode they may take out that 74ACT00, which drives them.

Let's hope that it is ONLY the 74ACT that has failed (and possibly one or more of the B170's)...
Can you check the resistance of IC3 pin 3 (that hot guy on the back) to ground? If it's low resistance, then it has likely failed. At that point we would want to check the resistance of the bottom end of L4 to ground... If it's low resistance then one or more of the BS170's has gone down.

Are you up for doing this work yourself?
--
Julian, N4JO.

To address a couple of those items...
1: The decoder is rather sensitive to the pitch of the resolved tone, in my experience. Aim for 700Hz, if I remember correctly. but experiment. ALso, make sure the programmed WPM is close to the incoming signal. The decoder will adjust over time, but it's helpful to give it a clue it by starting with something that is close. Also see "thinking" below...
2. S-meter not working, "Procedure as for the decoder helps": not sure what you mean by that... going into and out of the menu, maybe? Also see "thinking" below...
3. "When I change N1MM to another band the QCX will follow" : really? I hope not, QCX is a single bander... is there something special about the 160m QCX I don't know about??
4. "QRG is too low. For 1820? on the QCX RBN would indicate 1820.2.": Do you mean 1820 is reported when your VFO is set to 1820.2 ? You adjust the Ref frequency by the ratio of the errant frequency to the intended frequency. That ratio is -0.011%...Telling the system the oscillator frequency is lower causes it to compensate by increasing the VFO command.

Thinking... I believe the S-meter and the decoder are both driven by the signal at "AUDIO1" - I'm sure that Hans or someone will correct me if I'm wrong - so if there's an incorrect DC offset at the junction of R51, 52 and 54, then the A2D converter won't work properly. The voltage at that point should be close to 2.5V. If it isn't - especially if it's higher than that - it may be caused by a leaky C40.
--
Julian, N4JO.

Oh yes, that's definitely wrong: as you indicate with your arrow, voltages on IC7 are definitely low.
IC 10 is bad too, but let's address one at a time.

Assuming there are no solder bridges or bad solder joints...
If IC7 pin 7 is low, it implies that either its output is being pulled down (unlikely) or that it inverting input - pin 5 - is being pulled down (very likely). As both voltages at IC5 (which feeds IC6 an IC7) are good, it implicates IC7. The likely culprit is a leaky C9, pulling down IC7 pin 5.
Please do this:
First measure the voltage at IC7 pin 5, and see if it's the same as the voltage at pin 7: I'd wager it is.
Then, just for giggles... um, I mean "to enhance your understanding of the circuit operation", adjust IQ-bal while measuring the voltage at IC8 pin 7 (no need to put the unit in any alignment mode - we're talking DC offset here). I'll wager, again, that that voltage goes to match the voltage at IC7 pin 1 at one end, and the voltage at IC6 pin 1 at the other end. You'll figure out why that is by looking at the circuit diagram, but as a clue, R27 is a mixer...

Then I'd yeet (a Millenial term my son taught me) that C9 outa there and, if you haven't destroyed it in the process, measure it for leakage, then ceremoniously put it out of its misery with a hammer, and replace it with one you've tested for leakage.

Now to IC10.
Remember that it's supposed to be one half of supply voltage? That is achieved by R39, R40, and C24. 4.88V is OK if your supply voltage was between about 9.5V and 10V at the time you measured. You could check by measuring the voltage at IC10 pin 8 for supply voltage at the supply point to IC10. ALso measure the junction between R39 and R40. If IC10 pins 1 and 7 match that voltage, then IC 10 is essentially OK. The fact that pins 1 and 7 are the same is a very good sign.
--
Julian, N4JO.

I have a left over. Send me a mailing address and I’ll get it into the mail tomorrow.?

Colin
K6JTH

Hello Roger, ?I don't have the GPS unit so that's not it. ?Thanks for the suggestion, though. ?

Ron, to clarify, I just checked the center pole of the C1 to ground, confirmed. ?And to the ground ends of all the T1 windings, confirmed. ?And, as a special bonus ( and this one stumps me again), both the side legs of the C1 are common to Ground, too, and to the center pole. ?I have a hard time visualizing how the internal plates of C1 should actually be common to Ground. ?In my crystal sets the plates of the big vari-caps are quite well separated from each other. ?I've searched through my stuff and where I have a variety of little adjustable pots, like on the back side of the front PCB, I don't have anything even similar to the variable capacitor, C1, to play with and maybe figure it out a bit. Thanks for all your help and ideas. ?

Evan,
Per our private conversation I verified that the QCX was putting 5.3Watts to the qrplabs dummy load connected to the other end of the patch coax, so its verified passing RF correctly.?
Practice mode ON:
Diodes4, 9, 10, 2, 8, and 6 in with all stripes pointing toward T3.
Near V+ voltage at junction of D4 and D8. 11.8v.
Q3 gate RX=6.92v ; TX .046v.
Q2 Drain rx= .049 ;TX=-9.37V

Practice mode OFF:
Point F with RF. RX=.067; TX 31.7V

20 Meter amp.
I was actually hoping that I had a bad patch cable but thats not the case. The amp is producing about 30watts at 20V and about 15W at 12.7v supply voltage.

Thank you,
Bryan, n0luf

Hi Julian;
I measured the voltages on pins 1 and 7 on ic’s 5 thru 10 and they are all as you indicated. ?In order to take those measurements I had to remove the AGC board add on, doing so changes things somewhat. The oscillation is a squeal. It some times is present when power is first applied, if the volume is turned down most of the way the squeal goes away but signals can still be heard. When you turn the volume control past about 15 or 20 % the squeal starts, raising the volume doesn’t affect the frequency of the squeal only the volume. Without the AGC circuit the squeal is very intense. ?What I thought was motor boating was not present with the AGC removed, I assume it was the AGC trying to control the volume of the intense squeal. ? When keying the transmitter the squeal stops and the side tone is normal. The squeal returns immediately when receiving. ?This problem has been present from the start. I have been able to conduct some QSO’s by using semi QSK, but once the squeal starts there’s no stopping it. ?I have been able to complete some QSO’s when the received station is strong enough that I can turn the volume below the threshold of the squeal. ?The volume and sensitivity of this receiver seems to be very high. ?I find that I can have the receiver on with no problem the squeal only starts when the transmitter is keyed. I find that the impedance of my head phones is 24 ohms. I tried several other pairs with no effect.
thanks for your interest and time
Bill

开云体育

Hi Keith.

When you are doing the alignment, are you by any chance doing it with the GPS plugged in? That produces all kinds of strange results (Don't ask me how I know!).

Once I pulled out the GPS signal, my QCX+ aligned perfectly.

73

Roger

8P6RX

I've inventoried my QCX+ parts 3 times and am missing one 180pf (labeled 181) capacitor.?
Anyone know where I can get one without bothering Hans?
Tom AB5TN? (Texas)

Using magnification I can't find any shorts or crossovers. ?As for suspicious joints, if the solder has flowed on the back, and is visible from the front it's a mystery how the joint cannot be solid. ?But, I'll take the time to check component legs where possible vs the back side solder pad and see what I find. ?thanks. ?

So, today I plugged in and thought I'd run through it again. ?The magic number on the C1 adjustment was 7...then 6...then 8....then 7......with no hands on. ?I did adjust it a little and it finally sat on 8. ?So, I tried the three pots.....no change in the bar-graphs. ?Zero, zilch, nada..... ?so, back to the C1 screen. ?Oops now it's 6 again. ?And, after shutting down, adding headphones and powering back up, the injected test signal never goes off.....and although the multi-use knob does work on the Menu it DOES NOT work to change frequency of the radio. ?If I was stumped before, I'm really stumped now. ?Based on some questions posed by Julian I took a series of voltage readings on the ICs. ?Here's what I found. ?

For the time being I think a (tr)SDX is as close to a qsx as I am going to get and the chip shortages is making that harder to put together.
Jerry aa1of

I have a feeling this happened on one of my QCX's. It was a while ago and I can't remember which one.? Altering C1 wasn't doing much so I carried on and did the alignment of the three trimmers. Coming back again to C1 and there was now a noticeable difference when it was rotated.
Give it a try as it will sure be easier than pulling C1, if it works then that's all you need. Whichever QCX it was I never had that problem with the others and I have 5 of them.

Reg???????????????????? G4NFR

Thanks Bob.?? I like your simpler approach.?? Now to get my 3D printer working .... It is being temperamental lately.

take care and have fun.
73/74 Dave WA5DJJ
SUPER GRABBER

I had that same grey (or beige) desk at RCA.

I have designes a supercap power management circuit into one of my work projects, using the MAX38888:??
There are other models in the family.? Using it to keep a Linux system up long enough to do an orderly shutdown, or at least close files safely.??
Using their design tool you can use the system to wring the most energy out of the cap while still keeping it working within in a selected voltage range.? Charging it higher extracts more energy but lessens the life/temperature of the caps, the data sheet has a good discussion of this.
You design the circuit to be optimum at a given maximum current; the better you know this the more efficient the system will be as oversizing it will leave energy behind.?
I am using a 2-series constructed cell which is run at between 5.0/5.4V; there is a temperature/life/voltage tradeoff to make.

Note, I have no connection with Maxim except as a satisfied user.

73, Don N2VGU