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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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I’ve looked at those voltages and IC403 pin2 to ground shows 0.015V and pin 14 to ground shows 0V?

on IC405 all the voltages line up with what you’re saying they should be but on IC406 I’m getting 0V on all of those pins

Trying to add the image again...

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I forgot the first rule of radios - if something works, don't fix it.

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Anyway, I wanted to replace the diode that I have been using for the Rev 2 board modification with a smaller diode.? I replaced it and found that the radio would indicate high SWR every time I transmitted, so I put the original diode back in.? Now I can't hear any RF signals.? I can't even hear the "normal" birdies.? I'm attaching a picture of my "work".? Have I ruined L503?? I'm also afraid that I may have destroyed the trace at that end of L503.

Any suggestions would be helpful.? Thanks.

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73,

Mike, KL7MJ

On Sat, Apr 19, 2025 at 03:19 PM, Wiggle Pig wrote:

I have a QCX Mini on 40m which is a fine radio but the QMX feels more smooth somehow; probably psychosomatic!

That's interesting. I feel the opposite about my QCX Mini compared to the QMX. The QMX Mini receiver sounds better to my ears. Maybe once Hans gets around to eliminating all the SMPS-induced birdies, I will change my mind.?

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The heatsink question has been discussed to death here. I trust Hans' design and don't see any need to improve it. I've never blown the finals.?

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73, Mike KK7ER?

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Hi Scott. That usually happens when you install a blank IC2 without the EEPROM file loaded. I suspect something happened to IC2 when it was shorted. The easiest fix is to order a new firmware chip from Hans. Maybe your?Dad could add that to the order for the new rig. Doesn't hurt to have another one. If not too late he could change the order for the new one to be on a different band.

The other factor in all of this is the plastic package design. The heat sink practice for those other styles won't necessarily work here. The qmx design takes all this into account. Many cw qrp transmitters use 2 or 3 bs170 devices. Running digital waveforms provides a bit greater stress. Keeping the voltage at 12 volts or lower helps.?

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Curt

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