Hey All,
Hopefully your QMX build goes as expected and fires up just like it should…but if not, I can highly recommend the troubleshooting and repair services of Jeff Moore, W1NC.
Jeff quickly found multiple faults and repaired them, and sent a working QMX back to me. He has extensive experience with QRP-Labs radios and the expertise and equipment to find and fix problem components, bad solder joints, etc.
For me it was a great decision to send my QMX to Jeff for repair. If it’s over your head, Jeff can probably figure it out.
Jeffreym@...
73,
Jeff H, W4JSH
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Re: QMX rev 2 build dead and does not boot
Also, first check to see if the 12V input to the 3.3V regulator board comes up when QMX is told to turn on.
JZ
Frans,? I would begin by looking carefully around IC101, the 78M33 3.3V linear regulator. What voltage do you see at each of its three terminals?
JZ KJ4A?
Hello,
I have build a QMX rev2 but when I connect 12 volt nothing happens no current also not when I press the left rotory
It is completly dead also no usb device is detected at the computer, I see also no voltage at l202 to the micro contraller.
This my ever first kit wiich did not work i have build several such as QDC XCQ en WSPR tx GPs etc
I am a bit lost how to go forward where should I start? At the buck converter i see only 12 volt
Who can help me to get it working, or some testplan to proceed
73 Frans PE0F
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Re: QDX finals modification, imbalanced heating
Thanks Bruce! Once I have the finals imbalance sorted out I will try adding the hats and report back if I have anything useful to add.
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Re: QMX rev 2 build dead and does not boot
Frans,? I would begin by looking carefully around IC101, the 78M33 3.3V linear regulator. What voltage do you see at each of its three terminals?
JZ KJ4A?
Hello,
I have build a QMX rev2 but when I connect 12 volt nothing happens no current also not when I press the left rotory
It is completly dead also no usb device is detected at the computer, I see also no voltage at l202 to the micro contraller.
This my ever first kit wiich did not work i have build several such as QDC XCQ en WSPR tx GPs etc
I am a bit lost how to go forward where should I start? At the buck converter i see only 12 volt
Who can help me to get it working, or some testplan to proceed
73 Frans PE0F
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Re: QDX finals modification, imbalanced heating
Hi? Bojan? ?
Black anodised is helpful in terms of radiation.? Black paint on an already radiating metal surface rather less so (although it may look better)?
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Re: QDX finals modification, imbalanced heating
I believe that less than half the 'likely' cooling goes through the wires and that would be in the unlikeliest of cold board + cool air scenarios? (the Difference between BS170 and standard TO92 cooling model has never been fully explained by the maker)
?
Keeping the plastic package cool (say 40? - 45C)? rather than floating around 70C when under load ) will reduce the junction temperature by? around 20 C at 0.5W Pdiss? as it helps both the traditional Tjc path and the wires that first contact and then exit through the epoxy package and so can get cooled more/sooner at that stage too?
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QMX rev 2 build dead and does not boot
Hello,
I have build a QMX rev2 but when I connect 12 volt nothing happens no current also not when I press the left rotory
It is completly dead also no usb device is detected at the computer, I see also no voltage at l202 to the micro contraller.
This my ever first kit wiich did not work i have build several such as QDC XCQ en WSPR tx GPs etc
I am a bit lost how to go forward where should I start? At the buck converter i see only 12 volt
Who can help me to get it working, or some testplan to proceed
73 Frans PE0F
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Hi folks,
just completed my first QMX and apparently I haven't fried
anything. Good!
The build went fine and smoothly and after having already build
two QDXes, I had no trouble completing the build. Now I went
through the diags menus and the sweeps and it appears, that the
20/30m bands are weirdish off, whereas 80 - 40m looks all fine ...
For the 20/30 m bands I have (with dummy load attached):
- an Audio Filter Sweep with the yellow USB at -45/-51 db and
the red LSB at ~-70db
- an RF Filter Sweep with -43/-52 db at the center band
- an SWR sweep jumping wildly around between? 2 and 10 (whereas
the other bands are at 1 - 1.2)
Sounds to me like some LPF Problem on 20/30m regarding L510 &
L513, or is this rather an issue with the wired back jumper of
L401 23t to 23t holes (I did not do this with a cut-off but with
the overlength of the AWG28 wire.)? Or does this hint to something
else?
Thanks? a lot in advance folks!
Vy 73
Stefan.
--
Stefan U. Hegner <db4st@...>
* * *
DB4ST --- German Ham Radio Station
D-32584 L?hne ----- Locator JO42IE
* * *
GPG-Key | C3CC 23A4 FBA8 622B 48AE
F-Print | 4F19 D0EE E39E ABDC 2BCE
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Re: QMX Power Supply - USB Power bank with boost module?
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Re: QDX finals modification, imbalanced heating
Thanks Bojan! Dean, interested to hear your experience. Please check the other threads on TN0110, in particular it was mentioned that the higher switching speed could mean bigger kickback if used in QDX. I took this to mean you should plan to use Zeners also.
Some thoughts on the heatsink... If most of the cooling of the finals is through the leads, especially the drain, then keeping leads short is good. I then thought putting a heatsink on the board near the leads was reasonable (plus honestly, I had a heatsink in my hand and a big flat space open on the board and just said why not). On the other hand, most of the area I put the heatsink on was already designed to be a heatsink for the BS170s (but in the other direction!) so that makes it look pretty dumb. What I observed in this setup is that the heatsink does warm when the finals warm (but more slowly). Given the above, this seems interesting to me, but since my QDX has other heating issues I won't get more into it until the other issues are fixed. I also observed that?my finals stay below 100F while chasing QSOs at 5W FT8 (so say 25-40% duty cycle).
If you have the hat heatsinks also, you could consider tying them to the middle heatsink mechanically. If the fins form a solid interface this might start to make some sense, although still quite a hack to fit the not-designed-for mechanical situation. There are probably simpler and better options. Apologies for sharing half-baked parts of my setup; I tend to err on giving more information but I should have included more disclaimers.
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Re: QMX no Rx after a few days of operation
Thanks John
The key feature of this diode is that it's clamping function is only active during TX.?
During transmit the "RX" signal is 0V. So the diode clamps any signal at Q508's source to Ground + the 0.6V diode drop. The DC level at the Q508 source is already 0V via the 47uH inductor but this diode now also clamps the RF. Now it is impossible for any parasitic oscillation to build up, averaging DC 0V, with a negative excursion which pulls the source far enough negative that it's grounded gate causes a positive Vgs and causes Q508 go conduct got part of the RF cycle, causing potential large RF currents to flow in from the PA and potentially damage the MUX switch.
During receive we don't want a diode clamping to ground because we may worry that it could introduce intermodulation distortion. And with this diode, during receive, the RX signal is at +3.3V therefore the diode is reverse biased to 3.3V. It's far out of conduction and it's capacitance at 3.3V reverse bias is under 1pF which is way less than any stray parasitic circuit elements already present.?
I have tested it removing all envelope shaping entirely which is the harshest (and normally unmet) conditions because the body diode conducts harshly and deeply to charge up C509 when TX starts, potentially providing a large energy input to start the parasitic oscillation; this is easy to observe. When the diode is present the oscillation is completely suppressed.?
I also tested noise floor performance using -60dBm and -10dBm inputs at the BNC connector. This -10dBm signal is 83dB over S9... And reciprocal mixing dynamic range again with the same two signal injections. The measurements with and without the diodes were, within measurement variance, identical. So the diode truly has no impact on receive performance and appears to be an effective guard against parasitic damaging oscillation starting up.?
It's unclear what could cause MUX damage even after the C509, R510 and firmware trick. I did have a QMX here with a failed PA modulation transistor which basically means no envelope shaping, and that harsh RF onset could blow MUX chips. Or there may be some people who don't have the 80/20m swap enabled, who had upgraded from earlier firmware versions and not checked the parameter in the settings. Or there may be other as yet unidentified circumstances.?
Anyway this diode addition does appear extremely effective and without any impact on receive performance.?
73 Hans G0UPL
Important, not to be forgotten: Ishould add that Hans has already tested the diode change, as well, and is reporting good results.?
JZ
Klaus, Hans-Wilhelm,
You are probably aware that the QMX Rev 2 board initially had an issue with failing mux switches, the consequence of an engineering change that introduced a problem.? There is a post from Hans on the forum discussing this adventure.
The problem was that in TX undesired RF energy was making it through the T/R switch into the BPF.? Unwanted body-diode conduction at Q508 and inadequate clamping/dissipation of that energy was the cause.?
This energy set up a ringing in the BPF that could further self-sustain and grow to dangerous levels by driving the source of Q508 negative, turning on that transistor and allowing even more RF energy to enter. When positive excursions at the mux inputs exceeded 7 volts, the mux chips were exposed to failure.
Hans addressed this by reducing the size of the coupling capacitor C509 from 100nF to 1nF? and increasing the size of the associated pull up resistor R510 from 10K to 470K.
This dramatically reduced the injected energy and through the testing of dozens of LB and HB boards, proved to be a good solution. A firmware trick for LB operation was also invoked for more protection yet. Approximately 1000 new boards were modified to include this change.
It is possible that the change was inadequate to reduce the failure rate to zero. There are many, many variables in this equation.
Hans is considering a further modification to increase the safety of the mux chip. The idea is to actively clamp the source of Q508 to a diode drop off ground during TX,? but release that clamp during RX. He proposes placing a 1N4148 diode as shown in his sketch below. The diode would be reverse biased in RX, and out of the picture.? In TX unwanted energy and oscillation is suppressed by this diode clamp.
I have simulated this change for Hans and it appears effective with no down side. Logically, it appears very sound. I will expand my simulations in the next few days to try to cover more of those pesky variables.
If you implement this, your feedback is solicited as it will be valuable.
JZ KJ4A?
Klaus,
Yes, it appears something undesirable is going on with the T/R switch.
I would not advise attempts at operation until it is resolved.?
JZ
Dear friends,
just came back from my lab table and I guess the IC402 on my QMX is also damaged.
I do read 4.85 V at C406 as well.
R510 has 473.7 kOhm on my multimeter.
Don't know if the 74CBT3253C is extra sensitive to e.g. ESD or so, but may be some static is reaching the device from the antenna. IC402 is rated for 7 V supply voltage (absolute max.) and there is a 5.6 V zener diode (D108) on the plug-in board #1 which should give some sort of protection here.
Q508 is used as "RX on/off" switch. Something strange happening here which damages the IC402?
I can replace the 3253C here as well but finding the root cause of this failure would be worth spending some extra time for the investigation. Let me know, if there is anything else to test here.
vy 73 de Klaus, DG8RCN
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Re: QMX no Rx after a few days of operation
Klaus, This image is of the part placement of Q508, L503, and C508. Components L503 and C508 both have one end grounded. The diode could span between the two ungrounded ends, or depending on its size and construction, directly across the relevant Q508 terminals.?
Best wishes. OM...JZ
Dear John,
Thank you very much for the qualified and detailed explanation.
I will unsolder and replace the broken IC402 tomorrow and I will have a closer look onto the PCB how to implement the modification by adding the 1N4148 (MELF or SOD-123) the easiest.
vy 73 de Klaus, DG8RCN
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Re: QMX no Rx after a few days of operation
Dear John,
Thank you very much for the qualified and detailed explanation.
I will unsolder and replace the broken IC402 tomorrow and I will have a closer look onto the PCB how to implement the modification by adding the 1N4148 (MELF or SOD-123) the easiest.
vy 73 de Klaus, DG8RCN
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Re: QMX Clicking CW Sound
Durk,?
Not a wiring issue- older versions of Pico use the same output circuit & transistors. Only difference is the PIC chip and its programming. If I pull the PIC chip or the Pico battery, it doesn't hold the rig key down.?
I only use my UPK for MCW on 2m, so not really a big deal for me as I like the QCX's keyer and the QMX is tolerable as is. I'm sure it will get much better soon.?
--
73, Dan? NM3A
There are moments when everything turns out right .... Don't let them alarm you; they pass.?
-Jules Renard
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Re: QMX 60-10m mod last remaining issue: RX deep notch at 25MHz
I would also be very interested, and also have an unbuilt Rex 1 QMX to do it with.
73, Randy, KS4L?
On Sat, Dec 30, 2023, 8:58?AM Mitch NK3H < mitch@...> wrote: Hi Ryan,
I'm wondering if you ever finalized your hi-mid band QMX and posted the bpf/filter designs? I have a couple of unbuilt rev 1 kits and would love to have a unit that covers 40-10 for SOTA. Thanks and 73, Mitch NK3H
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Re: QDX finals modification, imbalanced heating
Peter, Thank you. I just placed my order for both heat sinks too. I like the idea you show in your pictures.
Dean - KC9REN
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Hello,
First, I would like to apologize for my bad English. I'm still learning.
I am not an experienced radio amateur, I am a beginner.
Initial commissioning my QDX:
My problem, when I test the transmitting with the command "Transmitter test" with Putty is the current by 80m 300mA by 12V.
The other frequencies has 600mA and more. I think, its not normely.
The same problem occurs when testing with WSJT and “Tune”.
Can anyone give me a hint?
QDX-Board: Rev 3a
FW: v1_10
version 12V
dummyload 50Ohm
73
Lutz
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Re: QMX in the K1USN Slow Speed CW contest
Hi Tom.? I did try the CAT interface in the past on the QMX in CW using TS-480 as the rig type in the N1MM+ software configurator.? It works fine and is a real pleasure to use the bandmap in N1MM+ to set the QMX frequency instantly? with spotting/call history and the ctrl-up or down arrows.? -Steve K1RF
------ Original Message ------
Date 12/30/2023 10:11:28 AM
Subject Re: [QRPLabs] QMX in the K1USN Slow Speed CW contest
Great job, Steve. I have found the QMX works great using the CAT connection to N1MM and have also played in the SST with it. I am sure it would play nice with N3FJP software if you want to connect it.
Tom K3AJ
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Re: QMX in the K1USN Slow Speed CW contest
Great job, Steve. I have found the QMX works great using the CAT connection to N1MM and have also played in the SST with it. I am sure it would play nice with N3FJP software if you want to connect it.
Tom K3AJ
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QMX HW Diagnostics: No TX?
I have newly built QMX rev. 2, 12V, low bands. Things seem generally good, though I'm still figuring it out.
I was reviewing the diagnostics, referring to the operation manual. I have two questions:
1. There is a little dip (one or two terminal rows) in the AF filter sweep graph. Around 2350 in 20/30m and maybe 2550 in 80m. Anything to worry about or to fix?
2. In hardware diagnostics, the transmitter doesn't seem so happy (screenshot below):
Transmitter voltage is at 10.2V even in receive. Red in receive, green in transmit.
Power shows as 0.0 W on transmit.
I have the unit connected to a QRP-Labs dummy load for testing.
What should I be checking?
Thanks,
Todd W2TEF
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Bruce Akhurst
Randy
Todd W2TEF