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Great, thanks!

No issues with this, Bruce.? I can see that the wire is still intact.? The broken top doesn't affect the performance.?

Hi everyone,?

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I have fixed this issue! It ended up being an incomplete solder connection at t501. I added some solder to the top of the board at this transformer and I have my on-screen s-meter, swr, and proper rf output shown in the diagnostics terminal screen! Hopefully this will help someone else in the future!?

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Cheers,?

Nick W4NPH

Hello QRPers,

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I'm having an issue with a new midband QMX (which is likely my fault!). I have no output power showing in my diagnostic screen after doing some testing with a a 20W QRPlabs dummy load. The coax is several years old now (Amazon special) and that's probably the cause.?

The QMX screen no longer shows the S-Meter upon transmit and the dummy load doesn't heat up anymore. The diagnostic screens show 0 Watts as well. It DOES have some RF going out though, as I did test this with an FT891 on 20/40m with the dummy load.?

I need some help finding the issue.

Thank you!

Hi Bruce,

This is a fairly common issue. I've had a few kits arrive with exactly the same damage. If the wires are intact and connected to the board, it should be OK.

- Bill? W3WJ

Curt,

Thanks. No, there’s no continuity.

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Mike

Bruce,

It's a fix described on the QMX page right below the Documentation header.? Here's a link directly to it

It's been a while since I posted this, so the fix may not apply to most folks by now.? My understanding is that just pre-2024 rev 2 boards need it.?

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Sorry about the photos, yeah they don't last for long on groups.io.? I've revamped my qmx kit since this post, and doing it again now to fit in a WB2CBA Pocket Tuner I'm trying to build into an Altoids tin, a kind fellow member on this board (thanks Eric) hooked me up with a PCB.? Condenses the kit size considerably.

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I just received my QMX+.? The shipping box and materials all arrived in good condition.? This appears the part was damaged either before installed or before the boards were sent to QRPLABS.

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Will this be ok or does it need to be replaced?

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Thanks!

Gentlemen, please add me to the list for a future group buy.? ? E-mail: kb9hv@...

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As a positive conclusion I have found that VarAC with its 500Hz bandwidth paired with the QMX and QCX 50W amp running at 13.8V (amp) gives a good 10W out on this digital mode.? Was able to successfully ping from Australia over Africa to the USA long path. The SSB is doing the job!

Another D109 failure here. I think. :-(

I have a QMX+ Rev2 that has been working for over a month. (SMPSs integrated into main circuit board)

Today I turned on CW practice mode for the first time...

As soon as I plugged in my iambic key (It works fine in a different QMX+) it shut down.

I tried powering up again and for a few iterations it would come on and then power off right away.

Then no response at all. Dead.

I suspect that this is just a coincidence and not the actual cause.

IC 101 and D103 were hot and D109 was scorching when I held PWR_ON. So I stopped active troubleshooting for fear of further damage.

I lifted D109 and the drain on Q111 and sure enough it comes to life with the 3v from the 3.3v linear supply.?

With Q111 still lifted, but D109 re-connected, it again, will not power up.

Re-lifted D109..

Actual measured voltages in 3.3v SMPS "bypass" mode:

VDD = 2.97v (from linear reg.)

VCC = 4.98v

ADC = 3.3v

+12V = 11.9

Seems reasonable considering, but the Diagnostic screen shows 12v+ = 13v, VDD = 6.6, and VCC = 5.6.

Can someone explain how those values are measured and/or calculated?

Source on Q111 = 10.6vdc. With a scope I see a PWM'd square-ish wave from +11.9 to +10. Not returning to 0. My suspicion is that this is due the Q111 drain floating.?

Thanks for your insights.

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Randy, N4OPI

Oh man!? Once again I am SO DUMB!!!? You are right!!!! My PS was set to 250ma max.? I punched it up to 2 Amps and the issue is GONE!!!!!!!

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Thank you !!!!!!!!!!!!!!

On Sun, Apr 20, 2025 at 10:29 PM, Kai Bouwman wrote:

IC403 pin2 to ground shows 0.015V and pin 14 to ground shows 0V?

I think this is not so typical. It would mean

For a broken IC403 I had expected the voltage at pin 7 and / or pin 9 are different from 2.5V. But you told early all pads from T401 are at 2.5V. Should IC204 be the culprit?

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Did you ever test the TX? If IC204 would be broken no signal would be produced for transmitting. But take care, one side of the PA is switched on all the time if you try to transmit in this status. Lower the supply voltage to 7.5V, connect a dummy load and try to transmit only for a short time, not more than some seconds and wait 30 seconds until the next test. Check the output and the supply current. The current should be not higher than 0.5 ... 0,8A. If you see an output of at least some mW IC204 should work at least "half" (CLK2). And check the voltage at the G of the BS170 when transmitting. For this please read QMX QMX_plus PA problems, broken BS170 section Diagnostics No. 5 to see which voltage should be found. If no signal is generated by IC204 you will find 0V at two gates and 5V at the other two.

This looks like a result from voltages at IC403 pin2 and pin14.

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73 Ludwig

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My QMX transmit is broken with or without the amp

Settings are (and were) as per your notes (transmit & 5V PTT enabled for each band).

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I have no idea why or how the amp killed the QMX since it works with other QCX radio.

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The QMX was fine in every way until I tested it with the amp.? Now it only receives.

It keys when I key it up but has zero power.

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Thanks for your reply.

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Ken AA7JC

Jamie, we are both correct!? There are at least 2 versions of the schematic, one uses Q4 and one uses T1.

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I hope all goes well with your surgery.? Check this thread when you are back among the cogent.?

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73,
Jim - AE5JE

I think I'm ready to give up. :(

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In trying to diagnose the above questions, I powered it on and the magic smoke come out of the BS170s.? I ordered more, carefully replaced them, and again the magic smoke came out of them the moment power was applied.? I have no idea what I did, and I'm about ready to throw the whole thing out the window.

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The only thing I can think of right now to help diagnose it is to put Zenner diodes across the BS170s to protect them from burning up, and then start probing for what's happening.

I suggest only troubleshooting this with no DC applied. Use ohmmeter.?

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See if L503 has continuity. If yes, it is likely okay. See then if you shorted something else.?

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Curt

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