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I've had finals in the QDX go many times while using an auto tuner. ?It seems like the damage was cumulative. ?I was using an LDG tuner and also the Elecraft T1. ?After swapping finals in the QDX about 3 times I quit using an auto tuner and went with the 4 State QRP tuner which also works as an SWR bridge keeping the SWR while tuning down to no higher than 3:1. ?I've never had a problem with the QDX ever since.

I will say that I had more fun with the QDX while using an auto tuner becuase I could operate remote using an end fed antenna. ?I would simply change bands in WSJT-X and press the tune button in WSJT-X and after it tuned I was ready to go.?

I lost one of the finals in the QMX due te a faulty BNC to SO239 adapter. ?I have since switchede to an MFJ manual tuner, tuning with a Rig Expert antenna analyzer connected first and then I put the QMX in line.

Curt
WU3U

Steve,

Before surgery, I would try to move Q103 a little by heating up the Tab until the solder melts and push Q103 over a little by inserting a small flat blade screwdriver between the bodies of Q103 and Q104. This is DELICATE work but you only have to move the Q103 part slightly (<0.5mm). Don't try to move Q103 until the Tab solder melts. Add a little solder on the iron tip and touch the Tab from the edge of the SMPS board ...do not get near the "short" end of the Q103 Tab. The reason for using a little solder on the iron is to better transfer heat to the Tab.?

73 Kees K5BCQ?

On second thought, I think the better solution is to go ahead and shave off the part of the Q104 pad that extends under Q103, and externally complete that net with a jumper wire. Less risk of a short that way.

Steve

Thanks Hans.

With the SMPS boards removed I have a short between Vdd and GND which wasn't there before I powered up having checked continuity on the SMPS headers.

Does this mean the MCU is dead?

Dale,

Try searching for "10mm speaker" and you will find some, one example here


73,
Yoon KM6KJI

Can you provide link to speaker??
--
Dale Hardin
KS4NS
Elberta, AL

Robert,

Yes that's the LM386 module I bought from Amazon. I didn't remove or replace the capacitor, but utilized it as the support for the control board with a plastic nut glued on the cap.

Because I pursue reversible mods, I didn't add a new hole for the speaker. I don't think it would make a big difference but you may try.

For wiring to the audio jack, initially I used only pin 5, and later I added a jumper between pin 4 and 5 because I remembered the manual saying that the left and the right audio channels are separate. Plugging in a earphone will disconnect the audio out to the amp of course, to mute the speaker.

Thanks,
Yoon KM6KJI

I've completed assembly of my first QMX kit. The instructions are extremely well thought out, and all went well.

However, during the final inspection prior to applying power, the inspection step 2.31.6 showed a very worrying thing on the buck regulator (you can actually see the same situation in the photo in the instructions):?
The power tab for Q103 extends out past the PCB pad, and actually overhangs the tinned pad for Q104. Although the actual Q104 pin is clear of the overhanging power tab, and I don't measure a short there, the tab and PCB pad are closer together than the thickness of a sheet of printer paper. The tiniest bit of conductive debris will short these points and destroy the unit.?

It's impossible to move the power-tab package, of course. I considered shaving off the edge of the Q104 pad to eliminate the overhang and improve spacing, but that would break continuity with other parts of that trace, so that's also a non-starter. I'm extremely concerned about the possibility of catastrophic failure from this almost-short. (In retrospect, I'm glad I didn't go ahead and wash the PCBs to remove the flux from my through-hole soldering, as that could easily have led to a short.)

The only other remedy I can think of is to apply a drop of thin cyanoacrylate glue to the gap as a conformal coating to isolate the tab from the pad. Does anyone know whether CyA glue is suitable or unsuitable for this application?

Going forward, I recommend adjusting the layout of the buck regulator for the next PCB run for the QMX to eliminate this issue. It has probably destroyed more than one apparently-sound QMX already...

Regards,
Steve

I don’t remember which cap failed in the past. ?There are several connected to VDD. ?Most likely is an IC. ?I can look at it for you if you wish. ?I’m in QRZ for an address.

Sorry for the third post.? Yoon, have you considered drilling a similar (maybe a little larger) hole like the Mic has in the QMX top cover (and make the hole black with a Sharpie)???? Looks like there happens to be an unencumbered area right over where the sound port of your speaker is located.? Would not even interfere with the VFO functions lasered (printed) info nearby.

Did you connect the amp input to headphone jack X401 pin 4 or 5 so plugging anything into the jack disconnects your internal amp input?? This to me would seem to be the way to do it.

I may just have to do this mod!? Again, nice work.

73,

Robert

Never mind!? Using "mini" in the search terms was the key: ? Remove the large cap.

73,

Robert, WA2T

Hi Yoon,

Nice work!? Try as I may, I do not seem to find that amp board on Amazon.? Lots of somewhat larger ones with a terminal strip and pin header, but not what looks to be a board with no I/O connectors, just pads.? Would you happen to have a link you could share?

73,

Robert, WA2T

The QCX although it uses BS170 uses a very different PA configuration, single ended Class E so may not be relevant.? The QDX and QMX use push pull Class D.
I have two QCX and one QCX mini none of which have had a problem.?
I have two QDX on of which had a failure of two BS170s, unfortunately damaging the IC 7400act drive by shorting the 12v to the IC output.? My QMX developed degraded output when one BS170 failed as a "resistor."?
I cannot be certain of the failure cause but there is high SWR when the auto tuner is trying to find a match.? This is consistent with the Elecraft warning "If your transceiver is not protected against high SWR, or if you’re not sure, use no more than half its rated power during antenna matching. This reduces stress on the final stage."??
The AT100 uses a very similar design to the Elecraft T1.??
?It is not fun to replace a BS170 and a real pain to replace a damaged driver SMD IC so I would rather be safe.??

Packages arrived this morning! Now to work out how to set it all up.

Hi. What about this?

On 11/09/2023 00:41, Bob Benedict, KD8CGH wrote:

? See the HamSCI Personal Space Weather Station project on measuring ionosphere movement by Doppler shift. HamSCI is building a net of receivers to monitor shift in WWV signals. I have a Grape 1 receiver running here.

Bob,

Thanks.
There is also a growing network using FST4W signals to measure shifts to 0.1Hz resolution and to measure the spectral spread of these signals.
This network is spreading worldwide.

The QDX with an external reference is used by a number of stations as a stable transmitter. One way it is done

The receivers are a little more specialised although a modified WSJT-X could make any stable receiver usable. Fitted with an external stable, accurate reference Kiwis and RX888s are amongst the ones used. Wsprdaemon on Linux is used for the measurements.
It started with WSPR but see the FST4W sections here .
All amateur bands may be used, the data is freely available.

73 Alan G4ZFQ

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Big big warning from something John Z? (who knows everything , though perhaps Kees? Talen or even? H Summer? deserves that title) said to me when discussing putting a Pi filter after a? direct drive? Ac08 chip as per my simulation.?

If the Pi section? is not properly terminated with a? matched resistive load the? Vout on the totem pole of the? CMOS might exceed VCC . If this happens the Cmos goes into Scr lock up.? Power has to be removed from Vcc to effect removal.? ?This is not really a problem if you are driving a? Transvtr and all conections are good and the designs are quality ccts.? It is a BIG problem during the experimental phase when you are soldering up the test cct and testing it in parts.? Be aware.

TEF

I've got thee of the original QCX'S, they have been subject to all sorts of mistreatment, forgetfulness ( no Antenne, wrong Antenne, broken AT100) whole days sending wspr and they are still going strong and in use, just wanted to say the fragility of the bs170 is not everybody's experience.

Paul DJ0CU G4ADF?

Well, I took Chris's good suggestion and ran with it. ?I removed all the switching supply components from the 5V board and bodged in an L7805CDT-TR 1A 5V linear regulator that I had on the shelf. ?It is mounted upside down on the pad previously occupied by L101.

The regulator does generate quite a bit of heat and consumes about 80ma more at idle than a "normal" 12V QMX, but I'm happy to report that the QMX works perfectly in this configuration.

The 5V board with the switching components removed:


The 5V board with the L7805CDT-TR in place. ?Power is routed from R106's previous position to what was previously the cathode side of D106, and ground is run down to the D106's anode pad.


Thermal image of the regulator. ?I obviously would have preferred to mount it with the ground side down for better thermal conductivity into the PCB but there just wasn't anywhere to put it. ?This is about as hot as it gets even after being on for quite a while.


Jonathan KN6LFB