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C604 is the easiest to remove and test. ?If that is ok, then it’s most likely one of the three transistors. ?If you have a scope you can look at various points to see what is amiss. ?Without that you are left with blindly replacing parts. ?No shame in that!

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73
Jeff Moore
W1NC

On Wed, Mar 26, 2025 at 08:12 PM, Steve N2IC wrote:

With all the BS170's removed, the Diagnostics screen shows the transmitter voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but maybe that is with good BS170's.

Hello Steve,

Diagnostics should show PA voltage near 0 when in RX mode or PTT ON only (no key pressed or key "P" pressed). The PA voltage should be high in TX mode (key "T" pressed). It's clear for good BS170 installed and the driver signals to the BS170 are ok.

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It should be the same when no BS170 is installed. A totaly open Drain of Q507 may go to a different value like Stan wrote. But the Drain is connected via R508 and R509 to GND and via R525 and R526 to GND. The situation should be close to good BS170 are installed and not switched on for transmitting.

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If you see 10.9 V in RX mode something is wrong, Q507 is broken or the voltage to the gate of Q507 is wrong or there is a solder accident around Q507. Please leave Terminal - Diagnostics. This will turn on PA voltage (for some reason) or try to turn it on. Check voltage at S, G and D of Q507. If all values are nearly the same, differences are only a fraction of a volt you have a high probability of a broken Q507.

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73 Ludwig

Hey (other) Don!

About the Group 5 handset:

No problem on readability. In fact they are probably a bit more "punchy" :-|

Yes, the mic is not operating at full output but I had to reduce mic gain to below 50 nonetheless. No pre-amps, environmentally stable, and all that. And I already had it in hand. Part of an old "what's that under the table" swap meet purchase. New in the box meant as a replacement I should imagine.

Aside from reducing the mic gain there was no other modification to the radio.

Even better would be an old military PRC-152 handset but that would take some modifying. Undoubtedly a bit lighter but truthfully I like the heft of this beast.

Although this does NOT fit in my pocket!

I prefer CW anyway. But it was fun.

72, Don

Thanks for your help, Stan.

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I think I'm ready to order some parts and some ChipQuik to deal with IC503.

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73,

Steve, N2IC

I was kinda counting on seeing that 10x signal! I will take you test sequence and report back. Thanks!

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73
Karl
KI4ZUQ

Yes, IC503 then is probably damaged - it often gets damaged with 'severe' blowing of finals.

And without the finals installed, there is no ground reference path for the bottom side of Q507, so you won't be able to properly measure the TX voltage.? It should be about what you measure without them.

Stan KC7XE

Hi Luis,

You should use the number of turns indicated, and ignore the nanoVNA results. The inductance value is from a theoretical model, the number of turns is what was found to work best in practice.

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Quoting Hans from the assembly guide:

"Note that the Inductance column shows the theoretical inductance modeled. This is only then a guide for experimentation during the
development phase, the practical result differs from the model inevitably. Therefore it is recommended to not get too fancy, don’t try to measure using an LC-meter etc., just count turns, evenly space them around the core, and let’s see how it goes."

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Stan KC7XE

Hi, all -

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Is there by any chance a button push to exit from the menu system back to

the operational frequency display, i.e., without having to do multiple EXITs to

navigate up and out?

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[I think the answer is "no", but thought I'd ask anyway.? If so, I'd like to suggest

something like "long press of the MENU button while in the menu system will

exit the menu system" ... very low priority, of course!]

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Thanks -

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Bruce K1FFX

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Sure thing.? TeraTerm Setup (this looks long, since I tried to be thorough, but it is simple):

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Step 0) In order to setup any terminal program, you first need to make the QMX COM port active on your computer.? To do this, first connect a USB data cable between your QMX and your computer.? Then, after it is connected, turn on your QMX (or power-cycle it if it was already on).? This should cause your pc to recognize the new COM port device.? It will have a number, like COM8: or COM10: (which you will hopefully be able to see in step 3 below). ?

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Step 1) actually a 'not' step: Don't connect any other program connected to your QMX, like WSJT-X, fldigi, or an SDR program or whatever - only one program can use the serial port at a time.

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Step 2) Open TeraTerm.? By default it has a very small screen, so I set it up with a larger font size so I can see it easier.? So (optionally) first select "Font" from the "Setup" menu,? and choose "Consolas" font at size 18 (or to your preference).??

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Step 3) Select "Serial Port" from the "Setup" menu.? In the dialog that pops up, there is a 'Port:' item with a drop-down selection box.? This has all of the numbered COM ports that are currently available on your computer.? Click on each numbered COM port in the drop-down box, and the information about that COM port will be displayed below.? The correct COM port for QMX will be the one that says "USB Serial Device" as the "Device Friendly Name".?? Select that port and note the number.? On mine it is COM10.? In that same screen, make sure 'Flow control' is set to 'none'.? The other parameters don't matter.? Then click 'New Open' to close the dialog and open that port.

Note 1: If you have more than one port with that same label, let me know and we'll add some steps on resolving which one to use.?

Note 2: If you don't see a COM port with that label, close the serial port setup box, power-cycle your QMX, and open the serial port setup box again to see if it appears.? Also see the note below about USB cables.

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Step 4) The screen will be empty.? Hit Enter.? The QMX 'Main menu' should appear, like magic :)? Learn all about how to use the various menu items in the QMX operations manual.? Most of them are quite obvious.? [A note about the Band Configuration menu you are looking for is just below].

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Step 5) Select the 'Keyboard' item from the TeraTerm 'Setup' menu.? Click the checkbox by 'Backspace key', and select OK.? This makes editing the numerical and text fields in the QMX menus work as expected using the backspace key.

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Step 6) In order to make this configuration come up each time you start up TeraTerm, choose "Save setup" from the TeraTerm "Setup" menu, and click 'Save'.? Leave the filename as-is so it will be the default.? Next time you want to connect, just open TeraTerm, and it will try to open the the same COM port with the same settings.? Then you just hit 'enter' in the empty window to bring up the QMX menu.

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Note: Use the same physical USB port on your computer each time you connect.? This is because Win10 will assign a different COM port number to different USB ports.? If you need to change USB ports, you need to update the COM port setting again.

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Band Configuration note:? The 'Band configuration' you are looking for appears as the first entry under 'Hardware tests'.? You need to enable your TX PTT and RX PTT settings for each band.? Change 'Disabled' to 'Enabled' by pressing 'E' on the keyboard (or 'D' to change it back to disabled).

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A note about USB cables: you must use a USB 'data' cable.? Some USB cables sold for charging don't have all the wires, and can only used for charging.? If you have a cable that hooks to your phone or another device and allows you to see data or files or play music or the like - that is a data cable.??? Less common cable connection issues:? A USB-A to USB-C cable is best, since some people have had difficulty in setting up with a USB-C to USB-C cable.? And on some computers there are problems with the newer high-speed (SS) USB ports; if you have problems, try a lower-speed port, or connect through a USB hub.

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I hope that helps - let me know if you have further questions or troubles connecting.

Stan KC7XE

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Hell forum,

please your help,

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I am building my QMX+ V3.

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On page 30 of the assembly instructions, there is a table were L518 is 268nH with 23 turns on the pink T37-0 core.?

This one turn less than L516 (435nH) with the same core.?

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Measuring with the nanoVNA, L518 with 23 inductance is about 100nH higher. To reach the 268nH, I have to reduce multiple turns.

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So here goes my question:

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Should I keep undoing turns until I reach the 268nH or should I ignore the nano VNA and keep the 23 turns?

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The same applies to L517, were the number of turns seams high for the target 316nH.

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The previous coils were very close to the target inductance.

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Thank you for your help,

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Luis

CU2IJ

I am headed to the post office this afternoon. If you ordered a kit from me (through today) it is getting mailed today. If you ordered a fully assembled mic, I am mailing about half of them today. Still working on making the other half.

Thanks for your patience with me while I had to wait for these cute mailers to get here from Amazon.

Ludwig,

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I don't mean to hijack this thread, but I am having a similar issue that I have described in another message. Here is the part relevant to Q507:

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"Now I'm looking at Q507. I ?have read Ludwig's postings on this. With all the BS170's removed, the Diagnostics screen shows the transmitter voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but maybe that is with good BS170's. The two SMPS look fine. "

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Does Q507 need to be tested with BS170's installed ?

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Thanks and 73,

Steve, N2IC

I've attached QMX to the PC and I see that it is on Port#003 Hub#004

Western Electric did a lot of work on audibility when they designed those carbon mic elements, their work is where the 300-3000Hz "voice" bandwidth came from.?

What kind of readability reports have you been getting???

I think those carbon mics were designed for 6V power; it might be a bit starved with 3.3V behind 2.2KΩ since the elements are about 200Ω IIRC.??

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73, (other) Don N2VGU?

Thanks, Stan,

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My scope is an old HP 1740A, 100 MHz. I changed probes, and now the input side of IC502 looks like a good square wave. However, the inputs and outputs of IC503C/D are not clean.? IC503A/B look okay.? I'm betting that IC503 was damaged.

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Now I'm looking at Q507. I? have read Ludwig's postings on this. With all the BS170's removed, the Diagnostics screen shows the transmitter voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but maybe that is with good BS170's. The two SMPS look fine.?

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73,

Steve, N2IC

I don't have this problem on any of my 4 QMX, so I'm pretty sure it's not just firmware.

Some ideas/possible fixes:

1) I would touch up the soldering on that encoder and its connectors to the main board, in case there is a cold solder joint that causes some intermittent when you put pressure on it.

2) It is also worthwhile noting that, unlike the other QMX switches, the signal line from this switch has a more complicated connection to the processor input.? Its pullup resistor is on the 5V SMPS card, which is connected to the switch via two sets of soldered-on connectors - so any flakiness in that path could cause a problem.? Also, its connection to the processor is not direct like the others, it goes through a FET switch (Q202), which has two associated resistors (R202, R209).? One person I helped several months ago had an assembly fault in R202 (it was dislodged), which caused the problem.

3) It is also possible you just have a poor encoder part, whose switch is more bouncy.?

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I would check those things to see if you can resolve your issue.

Stan KC7XE

Hello Stan! Thank you for your help. I've installed TeraTrm on my PC (Win 10). What should I do to let it find QMX? I never worked with Terminal programs before (

The signal at IC405/406 should be about 10x larger, so easily visible.

If your scope really lets you see that smaller 17mV signal (my cheap scope gives up well higher that level), you should be able to trace the smaller signal through the receiver section.? Look at IC 408 pin 5, the signal after the t/r switch, and then IC402 pin9, the output of the band selector mux.? Those two points will help see where the signal disappears.

One thing to check: make sure your radio settings in the Vara HF session has the "USB" mode selected, not "USB Digital".? If the latter is selected, the modem will switch your QMX back to Digi mode on transmit, which won't work on the higher speeds.