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Hi, I'm looking for tips to troubleshoot an issue with my QMX.

Its a rev 1 board that I have build for high bands and it worked great for a while, I have logged 20 QSOs. To be more precise, I was fine until firmware 017 was released and I enabled PTT for 20m to connect it to the 50W Amp that I had build previously, ran it at 12V as reccommended by Hans and got 18w or so of output. Did a few Ft8 QSO's and was quite happy with the result.

What happened next is where it when downhill. Had to try to increase supply voltage of the 50W amp to 20 volts to se if it was able of delivering 50w. It WAS :-)? for a few transmissions that is. Then the QMS when quiet, not able to send or receive anything. Display looks fine, able to navigate menus as normal. Back ground noice in the headset but no signals gets received, neither will it send anything on Ft8 or CW.

What have I done so far...?
I have done a factory reset and reflashed with 017 - no result.
I have checked supply voltage 3.3 volt and 5 volt - both looks fine
I have checked diodes (1n4007) using a multimeter - looks fine.
I have run swr analysis using usb via PC - pattern matches my antenna profile. (clear diff when antenna is discon.)

I have run out of ideas, pls. share you tips for what to check next...

Thanks
Per (OZ1KTC)

On Wed, Apr 10, 2024 at 09:36 PM, <Lytkemeyer@...> wrote:

Then the QMS when quiet, not able to send or receive anything. ... neither will it send anything on Ft8 or CW.
...
I have run swr analysis using usb via PC - pattern matches my antenna profile. (clear diff when antenna is discon.)

Is there an output from the QMX stand allone or not? Without prducing rf no measurement of the SWR.
Did you test the QMX without any connection to the PA?

73, Ludwig

No output from the QMX on antenna when sending. I connected a power meter direct to antenna conn.

I hear the dit and dat in the speaker and can see what I sending on internal morse decoder in display.
Power consumption is 120mA at 12v when receiving and goes up to approx 1.3A when sending.

It behaves, as if antenna is not connected to radio...

Correction, when running SWR sweep on 20m QMX consumes 1.4A and SWR needle show a tiny signal when at maximum sensitivity

Using HW Tests - Diagnostics, I see 0w output on all bands except 15 and 11m where it shows 0.1w and the needle on my SWR meter moves a tiny bit more.

On Wed, Apr 10, 2024 at 10:43 PM, <Lytkemeyer@...> wrote:

approx 1.3A when sending.

Very high, dangerous without a good load. For more investigation avoid sending and reduce supply voltage to around 7 V for short tests.
Please connect a dummy load and go to Terminal - Hardware tests - Diagnostics, press "T" only for a few seconds to transmit and make a screen shot while transmitting. Please post this here.

Do you have an external rf power meter?

73, Ludwig

After a longer troubleshooting meassuring signals using my oscilloscope, reading diagram and circuit layout, I found that Q508 had a melt down and is short cutting output.

Removed the little Bss123 FET and output was back at 3.5 - 4W
If I manually shortcut source and drain in receive mode, the receiver starts to receive again.

Need to go source a new FET

Thanks for your input Ludwig, I used the "T" at diagnostics during my effort with reduced supply voltage..

Fine you have found it. To much signal back from the PA?

Yes, that must have been it.
20 W output is plenty and 4X of what the QMX delivers.