Thanks for the tips. According to the diagnostics, the BIAS SMPS is fine, even though the output signal then becomes poor. I need to get some cold spray or something for further tests.
Apart from that, the behaviour of my QMX is getting more and more mysterious.
I used an oscilloscope to look at the signals at the gate and drain of the Q503-Q506. At the gate everything was fine, even though the RF output became dirty after a while. At the drain, the signals also appeared normal at first. From the moment the RF output became unclean, a twitching could be seen. I can hardly describe this with my limited knowledge of English. I suspect that the output signal is temporarily interrupted.
For further troubleshooting I removed L502 and retinned the wire ends. I don't know that that matters. Anyway, the signals at Q503 - Q506 are now about twice as high as the set frequency. I have no explanation of that. What could be the cause?
73 - J?rg, DG0JDE
