开云体育

Hello,

?

Was hoping I could get some help on how to troubleshoot my QDX.? I looked through the list, but was having trouble finding quite the right thing.

?

It is a QDX rev 3.? I updated it to the latest firmware, and then wanted to test the transmission before using.??

I have it powered by a benchtop power supply, limiting it to 9 volts and 1.3 Amps.

I have a dummy load fitted and am monitoring the signal across it with my oscilloscope.

Not transmitting, it is drawing 144mA at 9V according to my supply when connected to USB.

?

I went into the console application, selected "Transmitter test", and pressed "t" to transmit (on 40M)

?

On the oscilloscope I saw 40V peak-to-peak for about a second before it stopped transmitting.

The LED turns off while transmitting.? The QDX was still on and I was still connected to the terminal.

I can't quite catch what the power supply is doing (as it is happening too fast), but it *looks* like it is going up to about 850mA and not going into limiting.

?

Similar on 60M and 80Mt, though slightly higher power.

On 20M/30M, the LED goes momentarily and I see the power supply current start to go up, but never see a signal on the scope.

?

Other things I noticed

* The RF frequency sweep shows the pass bands being way off on all frequencies - the pass band looks way above where it should be (ie, 20M looks to peak a little under 15MHz, 40M is peaking around 8.5MHz, etc)

* Audio filter sweep looked fine.

?

Could anyone help suggest what I might have done wrong and what steps I should follow in troubleshooting?

Thank you!

-Ben

?

I should add that I built this for 9V per the rev 3 assembly manual (not the transformer manual).

Adding to this, I found this message /g/QRPLabs/message/93093

?

And started measuring the voltage on the diodes in different bands.

When I'm on 20M, D1/D2/D4/D5 are "high" (8.06V to ground when the board is running at 9V)

However, D3/D6 are at 4.7V when, according to the above post, it should be close to zero.

?

Measuring the X6 test point, only "2" is at 3.3V (the other two are at 1.8mV).

?

What should the voltage at D3/D6 be at this point?

Ok, I found that L4/L10 weren't soldered well.? Now I think I'm getting closer to right thing regarding the diodes, but still not sure they are quite right.

Running 9V, I am getting 7.2V across the diodes of the "off" bands and 0.67v across the diodes on the "on" bands.? However, the RF sweeps are still way off and it is still just transmitting for less than a second if that.

Please note that the bandpass filters are only for receive, so they shouldn't be affecting your transmit.? The low pass filters, along with the two binocular toroids are in the transmitter path - check them carefully.?

Right, I was noting the RF sweep because the low pass filters *do* affect receive, so the fact the sweeps are way off could mean something with the LPF section.? Or it could mean I messed up both transformers separately :)

?

After I fixed L4/L10, I have not been able to find anything else yet.??

?

Is there any way to check the binocular transformer without removing it??

On Mon, Oct 14, 2024 at 01:24 PM, Ben Sanders wrote:

Is there any way to check the binocular transformer without removing it?

Not that I'm aware of.? But some have found that they didn't get all of the enamel off the wires that solder into the board - especially with that thicker gauge wire which has thicker enamel.? Perhaps re-heating the connections with a hot iron can burn more of it away if this is an issue for you.? On mine, I almost caused an issue by inadvertently scraping some insulation off while I was winding it, which would have caused a short in the windings.? This happened because of the sharp ridges at the inner edges of the holes.? I saw it happen, and recovered from it while building.? I used a small knife blade like an awl to round off the sharp edges of the core so it wouldn't scrape anymore.?? And other than that, I just know that a previous poster here said he re-wound that transformer and it solved his problems.

BTW - I have a QMX, not the QDX - but they are very similar.? The QMX diagnostics have a LFP sweep which is very useful...

I'll look at removing T1 and rewinding it.

?

Thanks!

Ok, rewound it using the "WTST for 9V transceivers (“Weird Twisted Sisters Transformer”)"

?

And then I realized I am kind of slow.? I was thinking my oscilloscope was showing 40v peak, not 40v peak to peak (even though I posted the correct reading).? And that is correct.? So I didn't even need to rewind T1.?

?

The other thing is it seems that it only transmits in the test screen if you hold down the "t" button.? I was pressing it momentarily (as I thought it was a toggle), and that's why it was doing what it was doing.

?

I still have an issue where the RF sweep is off, but at least the transmitting chain seems happy.

?

Thanks!

?

Good!? I'm glad you found the issue, much simpler fix...

And before you do lots of work on the receiver, listen to it and see if it has good sensitivity.

And take a look at the QMX operation manual - unlike the QDX, it shows RF sweep examples for each band, and because of shared filters, some of the bands are intentionally "off-center" in the filter, yet work very well.? The QDX design is similar with shared filters, so take a look...

Stan