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Re: QMX - Looking for troubleshooting advice
I noticed that L509 is a 47uH inductor. Depending on the particular inductor model, the winding capacitance is usually on the order of a few picofarads, and the self resonance frequency can be as low as single digit MHz range. Above the self resonance frequency, the "inductor" appears as if it were a capacitor to the circuit. That may cause the LPF cutoff frequency to move lower. I think 47uH on 20m is probably ok in the majority of cases but I can imagine individual variability may bring it to an iffy zone in some cases. A smaller inductance may avoid this altogether. (Good to keep 47uH for the lower bands though.) |
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Re: QMX - waiting for Qcx part..
FWIW, my QMX volume encoder was faulty and had to be replaced.? The best way to confirm the functioning of the encoders is thru the terminal program and go to the hardware tab.? There you can confirm the proper functioning of all the buttons/encoders/keys.? My volume encoder on the left had a working push button but faulty rotator dial and had to be replaced.
AB4BA |
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Re: QMX - waiting for Qcx part..
Hi Matthias,
Mike stated that the left encoder should work, although the volume operation could be improved (Hans - maybe implement a log taper in software like most audio resistors use).? I had your issue with my first QMX that ultimately failed (be careful when testing when out of the enclosure - Pressing the encodes in can flex the boards and cause problems).? There have been updates to the assembly manual and posts on this server that point out possible shorts to the power connector (I have since taped that off for my 2nd kit). Verify that all 5 pins of the encoder are connected.? It is easy to think you have them connected when they are open or shorted.? In my case, it was the center pin of the side with 3 pins.? It was not soldered in correctly.? For my second build, I installed the encoder with the washer and nut before I soldered the leads.? I ensured the leads were as far in the holes as possible (Hans - maybe a suggestion for the assembly manual?). Do you get any sound out of connected headphones? 73 Evan AC9TU |
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Re: QMX - What's up?
Thanks, Cliff, your pictures are perfect.
I still suspect poor heat removal from the BS170s.? Can't prove it from here in Michigan though. If you decide to eliminate the sockets in the future, I suggest using low-temperature desoldering alloy to remove them.? Less chance of damaging your board. /g/QRPLabs/topic/92402784 /g/QRPLabs/topic/97094943 /g/QRPLabs/topic/98831808 Before you install new BS170s, clean all of the weird alloy off with desoldering braid and flux. |
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Re: QDX no RF out
#qdx
On Tue, Sep 26, 2023 at 11:10 PM, Evan Hand wrote:
Wow, I need NOT to use my iPhone to respond to this list server.? Sorry for all of the typos. The message should have been: 175 ma seems high. ?I would remove the 4 BS170s and see if the current drops. ?An alternative would be to disconnect one of the two leads of L14. ?Also, check if IC2 is hot. ?This is a potential IC5 failure again.? Good luck, and have fun hunting the issue. 73 Evan AC9TU PS: Hopefully, this does not come across as bossy.? If anyone, Hans Summers is the Boss.? I am just a volunteer responder not directly affiliated with QRP-Labs other than I have built many of their kits. |
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Re: QMX - waiting for Qcx part..
Push button should work fine. If you're having problems with double
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clicks then change the double click number to 500 in the menu (the default is 300). If you're having other problems with the push button you may have an issue with the control board. Make sure you are using the latest firmware. Volume control sorta works - what doesn't work yet if AGC. -mike/w1mt On Wed, Sep 27, 2023 at 9:07?AM Matthias Rauhut <matthias@...> wrote:
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Re: Deaf / mute QDX
Hi Nick,
The T button in the terminal transmitter test is a push button.? You need to hold it in to keep the transmitter on. When doing the transmitter test, what output do you get?? This would help determine whether it is in the common RF path for both receiver and transmitter or only a receiver problem. If power levels on transmit are OK, then as Cliff points out, T2 could be the issue.?? The sweeps point to the signal getting lost between C2 and IC10.?? I would verify that you do not have a connection issue with the dummy load and the QDX BNC. By chance, do you have a signal generator or a TinySA or NanoVNA that could act as one?? From what I have read, you do have an oscilloscope.? Verify that you can see the signal at a low level on your Oscope, then attach it to the BNC and trace it through the receiver parts of the radio.? You want to verify it is getting to the opamps IC7 and IC9 input.? They are 90 degrees out of phase between IC7 and IC9 at the output of the opamps.? An alternative to the signal generator is to add a temporary resistor parallel to R19 to boost the Sweeps generator so that the oscilloscope can measure the signal.? Here is the section of the QCX troubleshooting guide that explains the resistor bypassing: Signal generator injection into the front end The size of this resistor (120K) has been chosen so that when in the "8.7 Peak BPF" menu, the ADC is not overloaded, and a meaningful adjustment can be made. However, 120K series resistor into a 50-ohm load, which is approximately what the impedance of the transceiver's RF in/out is, means the 5V signal is reduced by a factor of 2,400 approx. This is a 2mV signal and it gets further attenuated by losses in the BPF and the mixer... and so it is way WAY too small to be able to view the signals on an oscilloscope.? In order to be able to trace an actual signal through the first few stages of the receiver, I first bypass R43 by temporarily soldering a 330-ohm resistor in parallel. This is easy to do on the bottom side of the PCB. Be careful to find R43, at the correct place on the PCB, using the layout diagram - it is right next to the BNC connector. Now the attenuation factor is only about 1/6th. It doesn't have to be 330-ohms. I wouldn't go below 220-ohms which will load IC3 too much and probably make the signal a bit too big; but 220-ohms, 270-ohms, 330-ohms, 470-ohms, 560-ohms... anything like this should be good enough. The later stages of the receiver will be massively overloaded. But we don't care - for now we just want to be able to see the signal as we trace it through the front end of the receiver.? The signal strength will be a bit more or less depending on whether or not you have a dummy load connected. It doesn't matter. We are only interested at this stage in seeing a strong signal that we can trace it through the first few stages. Here's the 0.8V peak-peak signal I see with the scope probe at the BNC connector. Which rev of the QDX has the problem?? If it is Rev 3 or later, another check is to verify that the 2.5volt bias is feeding back through IC3 and forward through IC4.? Since you have already replaced them, I doubt that one of them is the issue. The sweeps must be performed with a 50-ohm dummy load attached to the BNC. 73 Evan AC9TU |
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Re: QMX - What's up?
¿ªÔÆÌåÓýGyula,Thank you for your kind words. I used the same sockets on both of my QDX rigs, but built a bigger heat sink because there was more space. See my AE5ZA/QRP QRZ page for a picture. Haven't lost any BS170s since I did those. Now to get the same reliability with my QMX. 73, Cliff, AE5ZA
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QMX - waiting for Qcx part..
Just built a QMX successfully. The Qdx part of the tcvr works, ie. FT8. But for CW its still useless. The Volume Control is unusable.
As well as the push button function. Its not working reliable. Hope the future FW will solve it, whenever it will be ready. So for now the nice Trcvr rests in the drawer... ? |
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#u3s FST4W on the U3S?
#u3s
Hi Everyone,?
Is there any possibility that a future fw for the u3s could support FST4W beacons? Perhaps with the GSPDO it would have the clock stability to be a pretty nice little FST4W beacon, perhaps even up into some of the HF bands, no? |
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Re: QDX no RF out
#qdx
Evan,
Sure appreciate the help boss. I won't get to it tonight but I'll update you as soon as I can do exactly that. Thank you for guiding my troubleshooting!? Alex? |
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Re: Deaf / mute QDX
¿ªÔÆÌåÓýMy QMX went deaf yesterday after working for about 4 months. Found some questionable solder joints on T2 (QDX number). Fixed them and it came back to life so check them over.73, Cliff, AE5ZA
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Re: Deaf / mute QDX
On 27/09/2023 10:27, Nick Norman wrote:
Good morning all,Images attached - lets see what GIO do to them -- Worlds of belief, she [Susan] thought. Just like oysters. A little piece of shit gets in and then a pearl grows around it. (Hogfather) Wed 10984 Sep 12:40:01 BST 1993 12:40:01 up 3 days, 19:37, 8 users, load average: 0.50, 0.58, 0.60 -- 73 Nick M0HGU |
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Re: Report on new T501 winding style, and also eliminating L401
After thinking about your coments about the "new" winding method for the output transformer, the transformer should not increase in temperature. As you were having a reduced output power and the excessive heat, I think you may have had a short circuit winding on the secondary. Most of the RF was being dissapated in that short circuit thus heating up the transformer. By using the new method, you have removed that fault condition and are now getting the expected power out. The new method alone has not increased the power out.
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Re: QMX - Looking for troubleshooting advice
I fixed a QMX once that had a similar problem. ?I was stumped for a while. ?Then I removed L509 and replaced it with a new one. ?That fixed it for me. ?I think these inductors are pretty sensitive to too much heat when soldering them. The one I removed was more like a resistor and less like an inductor. ?Good luck. Jeff, W1NC?
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Deaf / mute QDX
Good morning all,
Here is the tale: At 09:15:45 on the 19th Sept my QDX went deaf - and subsequently shown to be mute as well (<0.6W all bands) The sweeps look horrendous! i.e. random noise essentially. Band switching appears to be OK The 25MHz clock is good There are out of phase signals on the gates (so IC5 is good) No excessive current (or heat) so I think BS170s are good. I have changed both the 3253 chips, no change. I plan to remove the PA FETs, re-wind the o/p transformer WTST style (9V) I plan to remove & check both the BPF & LPF toroids. Th terminal stuff all works as expected. (one question, is the transmit test a toggle action on T - i.e. T on ... T off, or is it a short burst of RF then off again?) As another point there has been no TX-ing with this unit for months, however there was an aerial failure some time since I last checked it & yesterday when I found the coax to connector junction damaged (by a tree). Any other ideas? Regards Nick M0HGU -- And it came to pass that in time the Great God Om spake unto Brutha, the Chosen One: "Psst!" (Small Gods) Wed 10984 Sep 10:15:01 BST 1993 10:15:01 up 3 days, 17:12, 8 users, load average: 0.36, 0.52, 0.60 -- 73 Nick M0HGU |
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Re: old verses new output transformer for QDX digital transmitter
'if it ain't broke, dont fix it' applies !!
I rebuilt my output transformer in my QDX as mine was originally wound for 9v, then modified, in circuit, for 12v and was a bit of a mess. I was also originally running my modified QDX on 10m with a consistent 2.5W (in WSPR mode)? out at 12.5V and 0Hz frequency drift. I never had the 10m resonance problem with this rig. I was hoping the 'improved' transformer would show an improvement on 10m and be a good basis to consider getting onto 6m with my QDX. Results with the removed, rewound and replaced RWTST windings for 12v again (no other mods at the time) , I now get 2.9W on 10m at start of a WSPR transmission, which gradually drops down to 2,5W over the first 30 seconds (input current 800mA), and I now get reports of freq drift (-1Hz) reported! So something is getting hot now. So in my case, I am wondering if it was worth the effort. Anyone else seen similar results? 73 Ken G4APB |
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