Yesterday evening I finished building my QDX and was quite proud of myself, for it was the first 'real' soldering project in ~8 years.
I already realized how old I have become when I needed a 20x microscope as an aid do scalpel away the Rev 3a ground short at C41, but it seamed to work.
Winding the toroids was kind of a challenge, but I photographed all the 0.3 mm wired once and double-checked the loops on the screen.
All the continuity checks in the manual where performed successful.
?
I used a lab PSU to power the QDX with 9V and limited the current, just in case.
All went well, LED stated flashing, then stayed on, as expected.
Voltage on the cheap PSU was fluctuating a bit around ~9.1 V to 9.3 V, current 160 mA.
I packet all and took it to my garden where I soldered before, hooked up the 20W dummy load and my Debian machine.
Connecting and upgrading the firmware worked flawless. I configured WSJT-X without problems as well, but I just tested sending on 40m.
This gave too much confidence, so without thinking much I connected my (maybe not perfect matched) portable backpack antenna, a 5:1 unun with a 2,7 m radiator.
Using WSJT-X I instantly received FT8 messages on 40?m, but my own CQ and replies where not answered. Current while transmitting ~ 0,5 A at 9,6 V (did not increase that on purpose).
Then I tried 20 m and during the first sending cycle I noticed a relay in my PSU clicking. In shock, I looked at the display, ~ 1,3 A and the voltage dropped.
I disconnected the PSU and inspected the PCB, no visible damage, but it now draws as much as I allow and the LED stays off.
The internal resistance on the power socket only 2,0 Ohm now.
I would really appreciate help to find some answers to the following questions.
- What did I fry and how to fix it? Voltage regulators? (I regret selling my thermal camera now)
- Any idea for the root cause? To my mind come:
??? - To high SWR on the antenna which was not matched at that location / position
??? - Current constrain in the PSU
??? - Mistakes I might made during assembly
??? - Errors on the PCB, possibly caused by the scalpel job
Pictures of the PCB are available, and I can investigate with a microscope if that helps.
73 Alexander DM8TE
Alexander