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First off, I would like to thank all those that offered help.? Especially Hans.? He recommended I replace the finals.? I did so tonight.? Start up went without any issues, then the LED dimmed and went out.? I was able to restart it, but same thing happened.? Now it will not stay on.?

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I am in no way bashing the QDX, or QRP Labs.? I believe it is builder error.? I do not know what the issue could be.? I see the trash can for this little device unless I can find someone local to help me.? I would buy a prebuild unit over a kit if the opportunity presents itself in the future.

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Thanks

73 KQ4SID

Craig

I’ve tried to power the mic externally, I didn’t know the QMX already provides bias voltage fir that. I will probably try to replace the stm32, if I can source one.?

Appy 3.3V to the mic input?? Why?????

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The KEY? lines (dit/dah) they would not like DC applied to them

hooked to the A/D which is ac coupled but a sharp transient

of 3.3V might just hit the input too hard.

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ITs 2.2K to 2.2V rail so that not? it but the A/D input are nominally

biased to half the Vdd (3.3V).? The mic input is though a .1uf cap.

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Likely killed the micro.

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Allison
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Post online only,?
direct email will go to a bit bucket.

Is Hans going to Dayton Hamvention this year?

How about a troubleshooting class for the QMX and QMX+ product line? Some discussion to common problems and resolutions to the problems. It would be great to hear from other technical specialists on this product as well. Perhaps some discussion on upcoming products and or FW revs.

Of course bring plenty of kits and parts to sell to repair the kits that have failed for whatever reason.

I would entertain coming to Hamvention for that alone.

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Don.

Hi Stan, thank you so much for your help, after the QMX died , first I thought I damaged the SMPS boards. I replaced them with the good working boards , but didn’t work. I started to thinking that damaged the processor unfortunately .

...and of course I got the wrong video link. (though that one is interesting, it's an earlier iteration)

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Here's the one I'd meant to post:

I came across this video elsewhere - hadn't seen it posted here and thought you might enjoy it.

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https://www.youtube.com/watch?v=P5jCYnwQscQ

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Looks like a custom bracket to hold the components together - rather slick and could apply to the QMX as well.

Allison,

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How about if I keep the amplifier on but remove the PTT cable.? The amp is on now, but not transmitting, and it's drawing 0.00 Amps.??

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Jim

K8DDV

First, a reminder to all:? Please DON'T CONNECT ANY EXTERNAL VOLTAGE TO THE QMX/QMX+ MIC/PADDLE INPUT.

For electret mics, QMX/QMX+ already has an internal 3.3V bias voltage hooked up to the mic input (ring terminal) of the connector.

And indeed, only electret mics, or other high-impedance mics should be used.? There is also an internal DC-blocking capacitor on the microphone signal.? The 'tip' and 'ring' terminals of this connector also hook directly to processor input pins (for the paddle dit/dah) in addition to the processor microphone input - so external voltages improperly applied may cause damage.

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Now, on to your problem (QMX won't turn on, per the message title):

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Looking at the schematic, I don't see how connecting 3.3V to any of the terminals of the mic input jack could cause damage such that the QMX would fail to turn on.? Unless there was some other factor, like perhaps an ESD event.? Or if the voltage applied for some reason was 6V or 9V or 12V, it indeed could have caused damage to either the processor or to the 3.3V power supply - this could happen, for example, if you were using a external supply for the 3.3V bias, and turned it from off to on while connected - some supplies can spike significantly above their set voltages when turned on, or spike well below ground potential when turned off.

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Since your QMX won't turn on, somehow either the power supply or processor was damaged - hopefully only the power supply, since it is much easier to fix/replace.? The protection diode in the 3.3V supply could have failed if there was over-voltage.? Or over-voltage could have fried some input pins on the processor, preventing it from starting up.

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A good measurement to make is the current draw while you have the PWR_ON button pressed (but don't press it too long unless you have a current-limited power supply set to about 250mA).? This can help tell what kind of fault is present.

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Then I would remove the bottom cover, and (with no power attached), and measure the resistance between GND and the three voltage busses (12V, Vcc, and Vdd).? You can find the contacts for those busses on the soldered SMPS connector pins.? (Someone just today or yesterday posted a message with a nice pdf identifying all of the voltage pins on the bottom of the QMX card).? I? suspect the resistance between Vdd and Gnd will be a low number of ohms (rather than a few K-ohms).? Such a low reading would indicate a failed component or short.? Next step would be to disassemble the top cover to get to the SMPS cards and remove them.? Then re-measure the Vdd/Gnd resistance on the main board - if it is still low, the processor is likely damaged.? If it is now high (hopefully), then the failure is on the SMPS card, likely D109.? You can use the nice procedure written in the wiki of this list to independently test the SMPS cards, or just order new ones from Hans and replace them.

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Good luck in quickly finding this, and ask if you have any addition questions.

Stan KC7XE

Without DC power you have no bias? for the diode switching so its high

loss for RX and tx.

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Allison
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Post online only,?
direct email will go to a bit bucket.

I've purchased the 50-watt amplifier kit, to be built for 80m, and bought assembled the 40m and 20m amps from Ray, VA7SK (very nice solder job, btw); on 40m it certainly makes a noticeable difference of 6dB -10dB on reports and it's much easier to reach Europe.

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Question: Can I leave the amplifier inline between the QDX and the antenna if the amplifier is off?? I'm not seeing that addressed in the assembly manual nor could I find an answer by searching the messages here.? I think so based on the schematic, but I don't trust my circuit reading skills enough to risk the QDX or the amplifier.??

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Thanks,

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Jim

K8DDV

With those settings turned on, you will be getting about 20dB lower of a signal from your mic to the audio path (compared to when the setting is turned off) - so it may be reacting with other downstream settings that require a minimum amplitude.

Crank up that 'global gain' parameter so the output of the EQ when 'on' will be similar to when 'off', and the choppiness should go away.

Yes, checked 80m also and it looks the same.

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I’ll have to look at phase predistortion, it is currently whatever default is, on I assume?

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73,

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Robert, WA2T

Hi Jim,

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L501 or C504 failure can cause these symptoms. ?Make sure to have about 2 ohms continuity on l501 at the pcb pads. ?It’s a little difficult to test C504 in circuit. ?These big tantalum’s fail though. ?You can remove it and test it on the bench.

It’s hard to diagnose the exact problems in the bias circuitry. ?There is interaction everywhere. ?But if you look around with a scope, you can often get a clue to what’s failing. ?Most often it’s one of the transistors, the coil being broken or the big cap failing.

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if you can’t find the culprit in that bias circuit, certainly send it along to me. ?

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73
Jeff Moore
W1NC

Too bad - I was hoping that L504 or L514 was broken, since they are so easy to replace.

To test L501, the 330uH choke, I would first test it for proper continuity through the circuit card by probing the devices it connects to.? That would be the top end of D502 and C504.? Those are the large-ish diode and capacitor along the sides of L501.? The top end of the diode is toward the edge of the circuit card, and it is the stripe on the capacitor.? This should show continuity (a few tenths of an ohm or so), and I would touch the coil while measuring, and apply a little pressure to move it around a bit to see if there is an intermittent connection.? Likewise with power on and in transmit mode, the voltage to ground from either of those points should be about the same.? If you look at the voltage on those points with an oscilloscope, you will see some saw-tooth-like variations at the frequency of the switching, around the DC value, with the capacitor side being somewhat more filtered.

I hope that shows something.? You can also check for continuity across L504 and L514 in case something is hidden there.

Stan

I noticed when I have EQ turned on, that I get choppy audio.? This happens when "Use EQ" is set to yes.? It persists while I am using the terminal or when I am out of the terminal or even when usb is disconnected completely, and after a reboot of the transceiver.? I am not sure if it is setting related or just an issue with the EQ functionality.

Jerry,

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When I look at the uBitx LPF, its structure is the same as that of a "shunt first" input Chebyshev LPF.? Does that mean it shunts the high frequencies to ground instead of a "series first" filter?? That would make sense to me as the capacitor in parallel with the input would tend to short high frequencies.? Or do I have that backward?

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There are some differences between the model and the HFSignals schematic.? ?C261 and C262 in the HFSignals schematic are "zero" values and not installed.? I also note significant distortion on the output waveform (across R1).? There is no LPF, so this may be the actual waveform.

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I attached the model with C261 and C262 feedback removed.? I also added the LPF arrangement for the v6, where all bands go through the 10m filter.? I did not change any of the other values upstream of the IRF510.? (the v6 has different feedback values in the emitter of Q90).

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Thank you for your knowledge sharing.

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73

Evan

AC9TU

Hans,

Adam,

I would not do that as the low-pass filter is designed to attenuate the harmonics of 20-meters so the second and third harmonics of 40-meters will exceed regulatory requirements.

Gary

W9TD

Hello,

I uploaded the charts of the simulation to

The simulation now creates all charts at once and is easily customizable.

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Now I can start with my experiments to modify the QMX20-10 to QMX17-6

I am aware of the fact that this simulation is not reality. But they give me the direction.

My first impressions:

- The BPFs are very broad?

- The 10m BPF could also work on 6m

- Very experimental: using the 15/17m LPF for 20m

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Vy 73 Peter?