Thanks everyone who has helped on this! I'm really excited about the QMX. Add another 80-20 rig here to the list of affected units, sadly. Adding some info, just in case it helps with the "why" investigation.

Configuration: 80-20m Rev 2 board wound for 9v

I completed my build just before going camping NYE with a radio buddy. I had flashed the (latest) firmware and done very minimal checks before heading out the door to meet up with him.
That evening, I got the radio hooked up and got it receiving on JS8Call, but no transmit. Got that worked out (fiddling with CAT settings, I think it was), and was ready to start some QSOs.
Although the antenna was resonant, I had my Elecraft T1 tuner in-line just to help check transmit output. I got tripped up by the new SWR? bridge protection disabling transmit when sending a tone to activate the tuner, then realized what was going on and worked out from the manual how to reset that (on the QDX), and put the tuner into bypass mode. At some point not long afterward, though, I found that I was no longer receiving anything. Antenna or not, regardless of band, nothing but static (like what you'd see/hear when no antenna is plugged in) on either JS8Call or the headphone jack. Sad! (Transmit still worked fine.)

I tested my sweeps when I got home and was able to put a dummy load on, and they (namely the image sweeps) look like what they're not supposed to according to the build manual.
Tested transmit again, and it was fine: 5v bang-on when supply voltage raised to 9v. Looked through all the bits of the diagnostic screen (in the serial terminal), and all looked fine there. (I can share screenshots of some sweeps and the diagnostics screen if desired.)

At this point, some comments in this thread (or/and maybe even tips in the manual) mentioned checking and re-soldering certain joints like those of T507. So I did some inspection - I could not see any problems, but resoldered some joints. No joy - still no RX.

When I was finally able to come back to this the other day, the issue had been tracked down to IC403, and I excitedly got set up to do some tests with the multimeter to check whether my board exhibited the same behaviour. Sadly, my board no longer powers up! :'(? When I push and hold the left knob, the board draws nearly 500mA for as long as I hold the knob down, then immediately back to zero current draw as soon as I let go. So I've got that to troubleshoot now as well. I tried looking for similar issues and resolutions across the QMX, QCX and QDX, but haven't solved it yet.

I've ordered a new IC403 and diode (two of each, actually), and am awaiting their arrival. Really hoping I can git this thing working again because I can't wait to use it portable and start making contacts with it! :)

Are you in practice mode? If you turned on practice mode, there will be no signal generated, the RF sweep won't work properly.
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73, de BD8BTE
op: Lun Yang

Re last:?

Hi Axel,
I am also using the ATU-100 and modified for a QRP use.
For the antenna tuning purpose I use a QMX?at reduced output power?with the 50W QCX PA connected. All supplied at +12V. This way both the QMX and the PA are operating at a safe margin whereas the ATU has enough input power to do the job. Works fine. However, it is not a very user friendly method to do.?
As I am using just a fixed antenna I then remember the ATU settings per band and then use a demo mode to manually set the ATU when in QRP mode. Again, not very user friendly and not applicable for outdoor use.
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73 Bojan S53DZ

Hello.?

You can reprogram the atu-100 so that it will tune from 1w input.? There are lots of instructions on the Web for how to do it.?
In the protection menu you can then adjust the tune % to output so that you transmit about 1w. On 40m mine I have to set for 55%. Then run the swr tune function in the hardware test menu that will trigger the atu.?
You will still have the safety of the swr protection but can also use the tuner.

Alternatively you could make an swr bridge that would sit between the qmx and the tuner.? you switch it in before transmitting. This would show a continuous low swr to the tx while allowing the full 5w to pass through to trigger the tuner.? The same as you would fine on the input of a manual tuner with an led.? I have not tried this method but I'm sure that would work also.?

Sam?
2E1OCT?

On Wed, Jan 17, 2024 at 07:12 AM, Colin Kaminski wrote:

You could defeat the SWR measurement in the QMX.?

You could defeat the SWR measurement in the QMX.?
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Colin - K6JTH?

Here are various FLIR images of a working QMX radio - Total output was about 2.5 watts (on 11 volts) into an antenna on 20M and a dummy load on 30,40,60 and 80M. The "shack" was pretty chilly this morning, but mostly these are pretty unremarkable. Nothing on the board got much over 100F.? The finals of course got warm, but nothing remotely concerning. It did inspire me to put a tiny bit of thermal CPU paste under each of them, which helped, but probably not worth the work, especially considering the amount of hours and good performance of this unit.?

The only completely expected thing I noticed was that different diodes would warm up between switching different bands. That's it. I haven't bothered to label any of these because they're frankly boring. Enjoy.?

Bonus is the standard dummy load after getting a few watts for a minute or two. Also boring.?

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On the QRP-Labs webpage for the QMX. Scroll down.

I have finished building of a QMX v,2 radio.? I can't find the address fpr downloading the firmware.? Where is it?? N7WM.

Pic showing CAT wiring to an Arduino acting as a USB to TTL converter
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73, Bernie, VE3FWF

Here you go

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73, Bernie, VE3FWF

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Is it true that the diode mod is only needed on the Rev 2 boards?

Paul -- AI7JR

And now it works, rf filter sweeps keep changing.

-- 
Paul -- AI7JR

And now it works, rf filter sweeps keep changing.

Now my swr sweeps show flat lines at 10. No power out when tuning in diagnostics. Swr protection trips. Dummy load attached.

Yikes. I really broke something.

I did a recheck of L401. Everything seems good. QMX was A+ 100% beofrw i attempted the diode mod.

The issues on 20m and 30m are new, after diode mod attempt.

73 K9PZ