Hi all,
Hoping someone may be able to help with this issue - but, first a bit of background: this all stems from operator error.
I got a small adjustable 12V regulator board to use between LiFePO4 batteries and the QMX and long story short, I did something stupid - I adjusted it, thinking I could use the voltage readout on the QMX display to know when I got it in the voltage sweet spot. I turned the the dial, the voltage didn't go down, so I quickly turned it again and *poof*, the 477J capacitor on the 5V SMPS board went bang.?
I shouldn't have done it, but lesson learned.
Anyway, I ordered replacement SMPS boards from QRP Labs and installed the new 5V SMPS. I was hopeful, but not expectant that the QMX would come back to life, because after checking what the voltage had been from the regulator I had been adjusting - it had showed just 7.4V, rather than the 13V+ from the LiFePO4.
The good news: the QMX came back to life with the new 5V SMPS, but with just one apparent issue.
The audio from the headphone jack is really low - if I put it into 4dB gain steps, and turn it a bit, I can just about start to hear signals and then as I get to the end, without the sound ever becoming remotely loud in the headphones - I can hear that the signals are becoming distorted from being overdriven. CW sidetone when I key is also very low, even at full scale.?
But the other thing is: the CW decoder on the QMX works fine, the audio from the USB-C output is fine - signals sounds great and aren't distorted at all when listening through my laptop with the USB-C cable and I've tested it successfully TX/RX with JS8Call.
I'm not sure how to try and diagnose/resolve the fault? - if anyone has advice or suggestions, I would really appreciate the help. I've done the basic things of trying different headphones, doing a factory reset and reloading firmware, as well as hitting the joints on the audio jack with the soldering iron again.
I'm assuming I cooked something, but I don't know what.
?
Thanks,
Dave
EI3HIB
