My 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.
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On Sep 27, 2023, at 04:27, Nick Norman < m0hgu@...> wrote:
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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On 27/09/2023 10:27, Nick Norman wrote: 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 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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Re: QCX Challenge - September 2023
I went on 20m with my QCX mini for the 1300z session and worked OK2BQN, DD6DO (both QCX) and OK/SO6A/P (rig not stated). No response to CQs around 14060 despite reasonable coverage on RBN.
Chris? G4CWS G QRP# 313
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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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Cliff,
you work very nicely. The winding is precise, the component position is clear and transparent.
I hope the sockets don't block the heat dissipation. I congratulate you.
--
Gyula HA3HZ
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What is the command dmesg showing when this happens??
Rebooting a Linux system often isn't needed. Just re-plugging in the device is good enough in most cases.?
--
73 Lex PH2LB?
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Re: QMX lost signals all of a sudden.
#qmx
Hi Cliff,
It's good to read that you have it working again.? You are correct that T401 issues should show up in the Audio Sweeps in the sideband rejection and opposite image rejection.? Hans does an excellent job of describing this in the operations manual for Rev 009.
Have fun with the radio!
73
Evan
AC9TU
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Alex,
175 ma seems high. ?I would remove the 5BS270d 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. ?That is a potential IC5 failure again.?
73
Evan
AC9TU
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Nevermind! I found that I can order it from you, which I just did.
Thanks. ? ? ?¡doug Doug Kaye, K6DRK DMR ID: 3196950 doug@...415.846.0940 ?
On Tue, Sep 26, 2023 at 2:15?PM Doug Kaye < doug@...> wrote: Hi, Hans.?
I want to buy two cases like the ones you use for the Clock Kit (~162mm x 123mm x 44mm) but with no markings, holes or cutouts. Can you tell me a source for these? Or can I buy them from you?
Thanks again. ? ? ?¡doug Doug Kaye, K6DRK DMR ID: 3196950 doug@...415.846.0940 ??
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Re: QMX RX BPF troubleshooting, a new clue
JZ, I already discussed that topic. If what you quoted is true and that¡¯s what I think, the receiver performance is no worse than predicted from the RF sweep trace. How big is the benefit? I don¡¯t know but I¡¯m not too worried about that. Quadrature sampling followed by active roofing filter is fairly robust against overload. One thing I don¡¯t know is whether the receiver gain is appropriate for the high bands. We¡¯ll find that out soon.
I would like to remind you that a major problem in the receiver is the difficulty in making the BPF perform as designed. Contrary to popular belief, Analog and rf engineering should not be about black art or voodoo tweaking but instead should be about understanding what is responsible for the discrepancy between the theory and the measured performance and how to fill that gap.
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Re: QMX lost signals all of a sudden.
#qmx
Hi Evan,
Thanks for responding. I may have found the problem.
I thought of looking at the sweeps an hour ago while looking at the schematic, but thought it was time to check soldering once again for good solder joints. Under a magnifying glass I found a couple joints that didn't look quite right on T401. Well they looked ok, but weren't perfect. Cleaned them up and resoldered making sure they were perfect and it began working. I'm not at all confident that I fixed the issue, but so far so good. Current draw went back to normal also. I'll be surprised, but happy if it holds up. When it works it's hard to find a problem so will keep beating on it and see what happens.
Sweeps look fine now, don't know how they looked before, but if T401 was indeed the issue they should have shown a problem.
If this fixes it I'll have to hang my head down again. Tough week.
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Hi Cliff,
Have you run any of the sweeps that verify the receiver is working?
What about the receiver on CW?? Can you detect stations through the earphones?
73
Evan
AC9TU
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It was showing 170 to 180 ma current before it went out. It used to be 150 to 160 before this episode. It still reads 170 now without computer interaction when powered on. My meter doesn't show the ones place in that estimate, I'm seeing .17 and .18 when I say that...so I'm guessing it was sitting around 175 and the meter was fluctuating on rounding.
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Re: QMX lost signals all of a sudden.
#qmx
Is the FT8 software showing an audio connection for both input and output.? Try switching between left. right and mono. I I imagine you've already done this)
I would try reinstalling the firmware.
Check the BPF inductor soldering.
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Re: QMX RX BPF troubleshooting, a new clue
...when we listen at 14 MHz.
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On Sep 26, 2023, at 8:50 PM, John Zbrozek < jdzbrozek@...> wrote: Since the input ?impedance response and bandpass properties of the Tayloe circuit change and slide along with the clock frequency, the self-test BPF plots we make with these radios are somewhat illusory. Each data point on the plot is real and valid as it is taken, but the overall network changes a bit as we change the clock frequency. If we are listening at 14 MHz and hoping to see signals at 9 MHz rejected in accordance with the measurement we made at 9 MHz, that expectation is probably wrong. The network that existed as the 9 MHz measurement was made no longer exists when we listen at 12 MHz. How big is the difference between the plot and reality? Are we better or worse off than what the plot suggests? Does it really matter? That is hard to say.?
JZ On Sep 26, 2023, at 4:58 PM, Ryuji Suzuki AB1WX < ab1wx@...> wrote: Indeed. However, I hope you now see that the complexity from the TX LPF side is much worse!
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Re: QMX RX BPF troubleshooting, a new clue
Hi John,
I have to disagree with the invalidity of the BPF sweep.? Granted that it might measure total response as the receiver's sensitivity could change, the receiver is being adjusted to the desired reception frequency each time.? This means the clocks to the Tayloe detector are changed so any impedance would follow.? The one point I agree with is that the measured results would not be the same as if the BPF were scanned with a VNA out of the circuit; in this case, that would not matter as the only adjustments available to tweak the response are the L and C values of the BPF.
For the purposes of tweaking the BPF, the included sweeps make total sense to me.? As for modeling the response, that might be a different topic altogether.
73
Evan
AC9TU
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Re: QMX RX BPF troubleshooting, a new clue
Since the input ?impedance response and bandpass properties of the Tayloe circuit change and slide along with the clock frequency, the self-test BPF plots we make with these radios are somewhat illusory. Each data point on the plot is real and valid as it is taken, but the overall network changes a bit as we change the clock frequency. If we are listening at 14 MHz and hoping to see signals at 9 MHz rejected in accordance with the measurement we made at 9 MHz, that expectation is probably wrong. The network that existed as the 9 MHz measurement was made no longer exists when we listen at 12 MHz. How big is the difference between the plot and reality? Are we better or worse off than what the plot suggests? Does it really matter? That is hard to say.?
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On Sep 26, 2023, at 4:58 PM, Ryuji Suzuki AB1WX < ab1wx@...> wrote: Indeed. However, I hope you now see that the complexity from the TX LPF side is much worse!
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Re: QMX lost signals all of a sudden.
#qmx
Hi Cliff,
Have you run any of the sweeps that verify the receiver is working?
What about the receiver on CW?? Can you detect stations through the earphones?
73
Evan
AC9TU
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HA3HZ
Lex PH2LB
Ryuji Suzuki AB1WX