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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So, as a bit more information (not all of it, obviously as you need to be security cleared for that!) I was thinking more of mainly increasing the thermal mass a little and perhaps trying to couple it to the case with a thermal pad or similar.

I have no real intention of using this unit for high duty cycle modes at the moment.

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I’m aware of the intention that the tinned pad on the board is the majority of the heatsinking but having done a fair bit of design and dev work on small RF units myself I’m all too aware that the mounting washer here provides the majority of the sink mass, with the pad and board structure also providing a good chunk. Given that the usual failure in the finals is through overheating, as a number of examples have shown, I intend to try to reduce that heat by sinking it a little better; replacing the washer with a better heatsinking arrangement will likely improve things.

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tra

Piggly

Very interesting, Jim ! I believe you meant Q4 and not T1, that is the base of the ‘3904.

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And so removing C1 is also advised (or lifting one leg). I believe there are 1/8” jacks that can be wired to do this when plugged in - that is disable a connection. I may have these in stock.

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I’ll be out of commission for ‘a bit’ - having lumbar spine surgery in the AM. But once I am cogent again, I’ll anxiously read what you’ve come up with. :)

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73, Jamie

WB4YDL

Hi all,?

My Dad just finished his QMX-mini build and after adjustments,(before casing) accidentally laid it on a spiral notebook and shorted something out. Now he gets the message “Use original IC”.?

The only reference to this in the groups is from 2017 where someone tripped a protection fuse in an IC and needed to update firmware I think. Any idea if this is a simple fix? Is it a hardware, software or both issue? This is the 20M version that uses IC2 AT mega328. Is the IC2 likely the culprit? Dad ordered another kit thinking it’s all fried but I suspect it can be a somewhat easy fix if we can trace down the issue.?

thanks all,

Scott

KF0OUH QMX builder (and SSB user :) )

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And that's with the QMX+. I don't hear it at all with my QMX HB.

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73, Dan - W2DLC

Don,

I've gone back to 027, but when I was experimenting with the 003 beta, I could hear a tone on 12 meters the strongest, then 11 meters, 10 meters not as strong because the noise level is higher, and on 6 meters. I could hear it weakly in digital mode, not at all in CW, very loudly in LSB and there was some time or greater noise in USB as well. This is all with a dummy load attached. It doesn't seem to be injected in the RF stages, but somewhere in the digital to audio conversion - maybe. I can still hear it in those bands with firmware 027 as well, but much weaker and only in digital mode.

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73, Dan - W2DLC