Hi Hector,

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alle the values are much to low, around -40 dB for the (real) peaks. It looks like a bad connection in the RX path. Please check solder joint of L401 towards IC402 pin9 for QMX Rev. 1 or towards "RX_IN" for later revisions.

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73 Ludwig

I like to participate in the ARRL FMT runs.?So . . .?

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I have investigated frequency response accuracy of my High and Low band QDX's, my HB QMX and my QMX+.

Don't have a QCX so can't speak direct to that model.?

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All have been within a hertz or two or better, right out off the assembly bench when checked with 2 different Leo Bodnar Precision GPS Disciplined Clocks units.? I have found that I can tweak the TCXO system setting by a few hertz , from as little as +2 to a high of +10 on one band for best frequency response.? Be advised that the best delta will vary a bit ( maybe 0.5 Hz worst case) from band to band in a given radio.?

I use FLdigi on the Frequency Measurement Test OpMode. Found it to be quite useful and instructive in showing things like warm-up drift, probable doppler shifts of received over the air signals and subtle changes ( hundredths (0.0x Hz) or less of shifts) just sitting on the bench in response to my heat or AC cutting on and off.? And there will be a bit of offset needed to completely correct for the FMT modem response on the particular computer on which you are running the FLDigi program.?

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Now having said that, I have spent hours measuring and analyzing over the air received WWV and CHU signals and its a rare band on a rare day & time, on a rare day of overall radio 'quiet' when the signals are rock solid as seen in FLDigi.? You have to be located inside the first skip zone of the transmitters for consistency in that.?

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And I'll bet for actual Ham Radio Operations, all the Q's will be just fine as assembled.?

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There is LOTS of interesting information, articles and How-To's for Frequency Measurement Testing with relatively simple and inexpensive methods these days.? ?Just give it a Google and wade in.? There's even a FMT-NUTS group.io.?

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GREG? KI4NVX

Hi! I recently posted about having some bad reception on my qmx after updating the firmware... Well it seems that it is something related to the hardware of my unit.

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I checked the RF filter sweep and it seems that my unit became a bit deaf.

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How should I proceed from here? What tests should I do?

This unit was working before, so my guess its that I messed up something?

This tests results are after a fresh firmware install and a factory reset.

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Thanks in advance!

73 de EA4IIF.

On Thu, Apr 3, 2025 at 04:35 PM, Greg McCain wrote:

WARNING: the jumper wire must sit flush

down on the board. Otherwise it will short

with the metal body of the SMA

connector!

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The JP218 jumper wires are well clear of the SMA connector, in front of it, not underneath at least on the Rev 3 boards. Maybe this was moved on the later PCBs.

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Chris, G5CTH

Stan, thank you for such a detailed dissection of this problem! I'll have to try the fix you described, today, at least the fix that doesn't involve a terminal, as I don't have the extra time (or desire) to become part of some worldwide de-bugging team.

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In the meantime I have been dealing with this by using Message 2, which doesn't seem to have the problem.?

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Do you happen to know if there's a list of recognized bugs to be fixed, so we can make sure this one's on it? (I'm assuming if it isn't on the list, it should be).?

Thanks again!

On Fri, Apr 4, 2025 at 11:11 AM, Matti OH6BEX wrote:

The QMX+ rev 3 does not start. With power button pressed, it takes 0.8 A current which slowly decreases to 0.5A.

0.8 A is to much.

Vcc and Vdd are around 0.1 V.

To start the controller you need Vdd at around 3 V. This voltage could be produced by IC101 but I guess there is a fault in the chain before. Pleas read QMX QMX_plus Startup to find this chain.

Testing diodes with a DMM: D108 shows 0.17V and 0.2V, D109 shows 0.11V and 0.12V.

meaning that both diodes are damaged. But as the diodes are in-circuit, these values are probably meaningless.

A broken D109 is affecting Vdd.

Resistances:

...

These values are not so bad and affected by the broken diodes.

I also received some spare SMPS'es and installed those to the older QMX+ rev 1 which I broke by accidentally inserting faulty SPSM'es from another faulty QMX.

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Receiver works ok.

Diagnostics page is all OK except TX Voltage which is RED showing 10.4 volts (DC input is 12.2V).

I guess you destroyed the PA and because of high current Q507 was following the PA in dead. Please don't transmit with a broken Q507 and read QMX QMX_plus PA problems, broken BS170 .

Apparently something in the TX chain is destroyed.

I have no oscilloscope. Is there something that I could check with an ordinary DMM?

Go to Terminal - Diagnostics (the controller will set a signal to switch off the PA voltage) and check voltage at D, G and S of Q507. If all values are nearly the same and high the Q507 should be broken. For more debugging check the Wiki page above.

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73 Ludwig

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Wait.? Not yet a member.

Will USA tariff laws affect the import pricing of Hans’ great radios/kits into the USA?

Hi

Tonight ZL4MDX and I made our first QMX+ to QMX SSB contact.? Myles, ZL4MDX is about 200km away.? Started on 80m and moved to 40m where signals were a bit stronger.? We both agreed that the QRP Labs equipment is exceptional in its performance.? Very well done Hans!

Greg ZL4GW

Thanks Stan.

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That power supply was labeled as 12 VDC output (just a wall wart). I was a bit surprised to measure 13.4. The reminder and caution on using it is appreciated. It isn’t the one that was being used for operation, that one was flaking out so I had to swap a different one in. May be time for a real power supply.?

I’ll get inside and do the additional diagnostics.

One thing I've noticed is that the Transmit EQ has a default Global Gain of -20.? Setting this to 0 seems to help with the gain.

Hello Stan, Ludwig and Kevin,

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I did'nt give up!?I ordered a mid-band QMX kit and it works good (but produces little bit too much power (6+ W) on 60 and 15 meters).

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The QMX+ rev 3 does not start. With power button pressed, it takes 0.8 A current which slowly decreases to 0.5A.

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Vcc and Vdd are around 0.1 V.

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Testing diodes with a DMM: D108 shows 0.17V and 0.2V, D109 shows 0.11V and 0.12V.

meaning that both diodes are damaged. But as the diodes are in-circuit, these values are probably meaningless.

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Resistances:

Vdd - GND 184 ohm

Vcc - GND 2.4 kohm

Vdd - Vcc 9 kohm.

These were measured with the DMM black probe at GND or Vcc.?

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But when I swap the probes, the readings are

Vdd - GND 1.2 kohm

Vcc - GND 313 ohm

Vdd - Vcc 1 kohm.

Why?

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I also received some spare SMPS'es and installed those to the older QMX+ rev 1 which I broke by accidentally inserting faulty SPSM'es from another faulty QMX.

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Receiver works ok.

Diagnostics page is all OK except TX Voltage which is RED showing 10.4 volts (DC input is 12.2V)

Pressing "T" changes TX voltage to GREEN 9.8 volts, power 0.0W and random SWR values.

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Apparently something in the TX chain is destroyed.

I have no oscilloscope. Is there something that I could check with an ordinary DMM?

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--

73 Matti OH6BEX

Hans,

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I appropriate the reply but wasn't expecting you to post back as I know you're away on your holiday.

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Thank you though. :-)

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Cheers,

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Mel. M0KMD.

On Thu, Apr 3, 2025 at 02:00 PM, mux_folder2001 wrote:

It is clearly not actually sweeping for some reason.

How can you tell?? You need to be monitoring the frequency to see if it is sweeping.

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Chris, G5CTH