My QMX just passed away - requiescat in pacem !
You might remember, that I built it in August (
/g/QRPLabs/message/107523).
I did only a handful of FT8 QSOs with it, to validate, that it is working and was not very happy with the instability of the CAT connection to WSJT-X/JTDX.
I did several firmware updates up to the current 014 firmware, but the CAT instabilities did not go away and other usage than for FT8 was impossible due to the missing AGC.
Today I wanted to use it, to record the output of a QSE (<-10dBm output), coupled through a 50dB attenuator to the input of the QMX.
Checking the signal through a headset was fine and then I connected the QMX USB connector to my laptop, to be able to record the QMX audio.
Most probably this killed the QMX, which was connected to 12V from a battery!??
Display of the QMX was off. I connected it to a lab power supply limited to 500mA and tried to switch the QMX on with the left button.
Current limit immediately applied and the QMX did not switch on. Even with a reduction of the supply voltage to 6V, the current limit still applied, when trying to switch the QMX on.
I have to say, that I completely lost the trust into the CPU controlled switching regulator in the QMX.
My guess is, that under certain situations during the handshake between the QMX and the PC via the USB port, the timing of the switching regulation loop is negatively impacted and the output voltage might raise uncontrolled.
I don't think, that I want to spent a huge amount of time to find out, what has been killed QMX internally, given the risk, that it might be the CPU...
--
73, DB2OO -Joerg
