Re: QMX+ bias current + output power fluctuating
Just realised that I never posted the resolution to this. After a lot of testing and investigation, we thought it was the processor causing the problems and Hans kindly sent a replacement main board which worked perfectly.
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This sounds similar to the issue I had - documented in this thread.? I spent time working though options with Hans and in the end he sent me a new main board. I think it was the processor that caused the issues.? Hans did have a lot of things worth testing and trying, so it'd be worth raising a support ticket if you haven't already. ?
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Assembled my QMX+ and it's working.? I had a couple of issues related to enameled wire not making good connections that were resolved.? I know it's working, I've made contacts on several bands successfully, including some decent DX, all on FT8.
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What bothers me is that the output power seems to jump around wildly.? If I go to the diagnostics screen and key the transmitter, the Bias SMPS shows fluctuations in current that correspond to the fluctuations in the output power.? The Duty cycle on the Bias SMPS always shows 0%, even as the current jumps around in the red.
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I suspect I've managed to damage one (or more) of the surface mount semiconductors.? At least that's what my reading on the subject would seem to suggest.? What I need is a test that can be done with a multi-meter that would shed some light on the problem.? I can probably resurrect an oscilloscope if I need it, but I'm hoping someone can lead me to a simple voltage or resistance test that could help isolate the problem.
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My last problem was related to soldering and enameled wire which was easily resolved.? I'm hoping this issue can be resolved without major surgery as well.
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Thanks in advance for all of the good advice I'm about to receive.
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Andy
WB9YXA
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Hi Stan, thanks for the speedy reply. Appreciate your insight. I am getting continuity from C403-Pin 10 and from the "15-turn" tap of L401a to Pin 6 of IC402. Seems like that's good, right? I had noted the different layout around IC402 between Rev 1 and Rev 3/4, but wasn't sure how that would affect the build, if at all. Perhaps that is part of the issue though.
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Here is my RF sweep for 20m:
And the LPF sweeps for 20-15m:
Best,
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Alex N7ADH
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Yes you need a dummy load for calibration and yes with bit of practice you can use the built in swr meter for antenna tuning.
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Hello, i'm sorry for asking newbie-easy questions. Do i need dummy load, perform any possible calibrations if will receive already assembled and tested QMX+? Can i use built in SWR sweep and meter for tuning my antenna? I'll use it mostly for digimodes.
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Hi Alex,
This is an interesting one.? For more context, it would be helpful if you posted RF sweep for 20m, and LPF sweeps for 20m, 17m, and 15m.
The bandpass filters (RF sweeps) follow the LPFs in the receive path, so they interact.? If the LPFs have a significant attenuation, it will cascade to the BPF.? Also, 20m and 17m use the same BPF turns (all of the turns on L401a), so it is helpful to see where that full filter is centered, so it can be moved appropriately.? 15m has its own BPF, made of just the 15 turns before the tap, so we should be able to center it at the peak of the filter.
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Note that the Rev 1 board wires IC402 to the BPFs very differently than Rev 2 and above.? Look at both schematics to see.? In Rev1, the capacitors go into the Y inputs of IC402, then the corresponding W output of IC402 feeds the toroids, which are then input to the X inputs of IC402, with then the full L/C filtered signal at the Z output.? In Rev 2 and above, the L/C are combined first, and fed only to the Y inputs of IC402.
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Since you are using the mid-band kit, which on Rev 1 will use all 4 of both the X and Y inputs, make sure that the 4th input of each is really connected for C403 and the L401a tap at pins 10 and 6 of IC402 (it doesn't show on the schematic, and I don't want to take mine apart to measure :).? But I suspect the board has the connections, otherwise you wouldn't have had holes for C403.? So this is likely not a problem, but the careful inspection may be instructive.
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Stan KC7XE
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Startup issues with QCX Mini (Rev. 3)
Hi all,
I've just finished building a QCX Mini (Rev 3; software version 1.09a; 30-meter version). When I powered it up for the first time, I got the intro screen followed by a 160-meter frequency. Having read the advice to do a factory reset if I didn't get a band select screen, I attempted to do that, and that's when my problems began. First, going to option 7 (other) and then heading for option 17, I found that the menu options stopped at around 9. Then, once I tried to move past that point, the display either went blank (still fully lit but no info) or started producing gibberish. After cycling the power several times (and waiting 30 seconds or longer before powering up again) trying to "get lucky," the display now goes to gibberish after option 4 or 5 on the main menu. Any thoughts on what the issue might be and/or how to try to resolve it? Many thanks in advance.
73,
Rich, W2VU
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On Mon, Apr 7, 2025 at 08:31 PM, <andrey@...> wrote:
I used a lab PSU at 7V initially; QMX draws ~150 mA right away - not proper.
150-200mA is fine for QMX without firmware, in firmware update mode presenting USB drive.? Assuming the current draw happened after you pressed the power-on button.
But at the same it did power-up and display lights up.
If display light comes on without firmware installed, there is a problem.? It? uses 5V power supply, which is only started by firmware.? Are you sure this happened with no firmware installed?
So I tried USB connection and was able to flash the firmware successfully.
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- it self-turns on;
- MCU probably thinks it is underpowered: as soon as it boots and displays normal view, it shows "Shut down!" and cycles;
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If it 'self? turns on', and then does 'shutdown', without you pressing the power-on button, it likely means the power-on signal is stuck in the 'on' position.?? That would cause it to self-turn on, and the MCU, after booting, would see the power-on/off button asserted, and do its shutdown sequence.
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So the first thing to do is verify the power-on button from the encoder, and all of the connections of the PWR_ON signal to the main board (see the schematics, it goes through pin 1 of the 8-pin).? It is likely that the signal is shorted to ground (or to another low signal, like the adjacent PWM_5V pin) somewhere along that path.?
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This could also cause the display backlight to flash, since the MCU will start up the 5V, but then quickly shut it down again because it thinks you are pressing the power on/off button to shut it down.
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First solve that issue, and keep using the 7V supply, and then we can investigate the high current draw if it isn't resolved.
Stan KC7XE
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I'm have not seen this behavior before, so no, it is not a well-known issue.
Perhaps RFI into your QMX or computer from imbalanced antenna?
Try adding common-mode choke to your feedline, and/or ferrites on your USB cable.
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Maybe others have ideas...
Stan KC7XE
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One question: which version of kit did you have?? v1, v2, v3, v4?
There are several different possibilities for a burned Q109.
All of them come from a short on Vdd or one of its control lines (LIN_REG_EN, PWM_3V3).
These shorts could come from solder bridges, or a tiny flake of solder that migrated somewhere, or from mechanical issues: the tolerances are very close when assembling, and metal surfaces can easily touch together.? So in addition to inspecting soldering, also look very closely at the assembled unit (without bottom cover), and see if anything from the various assemblies is touching.? Typical issues are the LCD mounting tab that needed bent over, the 10 pins connecting the display to the mount board, the encoder bodies, and the back side of the power connector - maybe others.? Also the soldering of the connectors to the SMPS: the connector 'pins' are a bit longer than the pads (if not trimmed), and can touch or create solder bridges to other SMPS components on the top side.
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After inspection, first thing to do is measure resistance to ground on each of Vin, +12V, VDD, and VCC, on the main board, without the SMPS installed.? And then the resistance between each of these voltage rails.? The resistance to ground should be at least a few k-ohms.? There should also be at least a few k-ohms isolation between each of them.? Also measure the resistance on the control pins to both 3.3V and 5V SMPS (PWR_ON, PWR_HOLD, PWM_5V, LIN_REG_EN, PWM_3V3).? They should have no continuity to any other pin on the connector, and have a high resistance to ground and Vdd and +12V.
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Hopefully those inspections and measurements will show something that could have caused the over-current that burned Q109.?
Good luck, Stan
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Tony,
I have added the results for 9V:
10V???9V?
Band?PWR-W?I-mA?PWR-W?I-mA
160??6.55??1150? 5.19?1047
80???5.35?? 928??4.24? 851
60???4.99?? 925?3.92? 859
40???5.73?? 975?4.49? 898
30???5.68??1363?4.45?1256
20???4.86?? 931?3.89? 872
17???3.57??1258?2.95?1189
15???5.73??1613?4.86?1532
12???3.89??1553?3.45?1486
10???5.05??1282?3.97?1182
6????3.87??1080?3.61?1068
Regarding lack of sufficient drive, I don't think that is the case here.
DL4JAL has designed a CW only 5W transceiver, which uses the same set up as the classic
'Sierra' using band modules to change bands:
https://www.dl4jal.de/cw_qrp_trx_bm10/cw_trx_bm10.html
The power amplifier is inspired by the QMX+, but he uses Mitsubishi medium power fets with
bias power control instead of BS170's and claims 5W out on all bands.
73,
Roelof, pa0rdt
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Roelof Bakker, pa0rdt
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Hello Wilson,
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I suggest you first remove both power supply boards and verify that there are no shorts on the Vcc and Vdd lines.? The pin assignments from the bottom view of the QMX board are in a PDF.?
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I assume this is a QMX and not a QMX+.? They are different in board layout.? There are also differences in board revisions.? Supplying the volunteers with both helps us give you better suggestions.
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There is also a test process in the files section of the group for the power supply boards:
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I hope the above helps.
73
Evan
AC9TU
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The 3.3v SMPS provides power for the STM32 controller. While you are waiting for new SMPS boards, I would check resistance between VDD and ground per to rule out a controller short, per the wiki. /g/QRPLabs/wiki/37422gl de Russ, va3rr
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I received a QMX and built it.? ?I've built a number of QRP kits all successfully, but not so for this little guy.? I attempted to powered up using a regulated power supply at 7v and 250 mA but without success.? In my efforts to get things going, I resoldered every joint and inspected for bridging.? ?In the end, I clearly identified a component (Q109) on the 3v power supply that had a hole melted through the package.? ?I've just order the spare power supply boards from QRP Labs, but don't know where to look for the cause of the current failure before installing and destroying another 3v power supply.?
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Any ideas for me.
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Regards,
Wilson Little (NT5AT)  ?
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This is a little off topic but the charges to deliver my natural gas is almost twice what my actual gas bill is each month. It's happening everywhere.
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Re: Release of version 2.0 of ABS solution for QMX+ (Automatic internal antenna tuner, internal battery and internal speaker with audio amp)
#PSU
#QMXplus
#audio
#ABS
#ATU
Also, there's a rule that the envelope must be flexible to get the low rate. In the case of international USPS mail, it is very punitive. If the envelope is not flexible, it is price the same as a box!
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Cal AD8Q
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On Wed, Mar 19, 2025 at 11:26 PM, Stan Dye wrote:
On Wed, Mar 19, 2025 at 06:15 PM, Jerry Gaffke wrote:
We could ship a QMX+ main board with the auto-stuffed surface mount parts installed (2.5 oz) for $0.73
Unfortunately you can't.? There is another rule that says if the letter is over 1/4" thick, it goes into a new rate structure - and I would never send a card like that without a bit of padding to avoid destruction in the postal service machines, so it will definitely be over 1/4".? I think those 330uH inductors by themselves are over 1/4".
Stan.
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On Wed, Mar 19, 2025 at 06:15 PM, Jerry Gaffke wrote:
Shipping small items up to 3.5 ounces using first class mail within the USA costs $0.73.
Same as sending a letter to your mother.
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Re: QMX snags epic DX during greyline!
La Réunion island
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Jean-Jacques - F5IJO
FISTS#17008 LICW#5902
Le 08/04/2025 à 17:27, Dan Quigg via
groups.io a écrit?:
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Congrats!
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Where IS FR8UA?
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Dan
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Re: QMX snags epic DX during greyline!
Congrats!
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Where IS FR8UA?
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Dan
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Hi Roelof,
Interesting result with 2x3 BS170s. What is your 2x2 output?
Something I have been thinking to try is stacking a second ACT08 on top of the existing one. My simulations seem to show that gate drive is very important.
Is your build a 12 volt or 9 volt build?
Tony
AD0VC
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Hello all,
Last week I finished the build of a rev1 QMX+.
No problems were encountered and it worked fine on powering up.
During the build, I have measured the frequency response of the low pass filters.These appeared to agree very well with a simulation carried out with help of RFsim99.
One anomaly was encountered: the series resonance of L507, a RFC feeding DC to the centre of the 60M-80M low pass filter caused an additional loss of about 0.5 dB just in the 60M band.
To get rid of it the Q of the RFC was lowered by mounting a 2K2 SMD resistor in parallel of L507.
I have been reading that many builders experienced a drop in output power on the higher bands and my build was no exception.
As I like tinkering a lot, this appeared to be a nice challenge to see if this 'issue' could be improved upon. My build is for a supply voltage of 9V.
Reading up on this issue on this list, it appears that the output transformer L501 is critical. Muhsin, TA1MHS, wrote that he had replaced the BN43-202 binocular core with a BN-61-202 core, which improved
performance on the higher bands.
Apparently a lower inductance for L501 helps. I did not have stock of a BN-61-202 core, but I? had a BN-43-302 at hand and wound a WTST on it for 9V operation. The change in output power was negligible,
though.
The next thing I tried was using 2 x 3 BS170 instead of 2 x 2. Powered with 10V, gave these results:
...
This more or less solves this issue for me, though I don't think this is recommended in actual operating.
I wonder what the reason is for the much higher current consumption on e.g. 15M compared to 80M, whilst delivering about the same power? A matter of lower impedance?
Anyway, this is great fun.
To be continued.
Test gear:
Sensor Monitor Power Meter
100W dummy-load
Rigol DSA-815-TG spectrum analyzer
Lab power supply 0-32V 2A
73,
Roelof, pa0rdt
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Roelof Bakker, pa0rdt
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ZL1SGS
Richard Dyer
va3rr
James