The D109 failure of my QMX was apparently caused by a short 12V power fail.
I didn't notice that my DC power plug is a 2.5mm size plug, and did not even know that there are 2.1mm and 2.5mm versions.
Well, it worked OK perhaps 10 - 20 times until I somehow touched the plug and the QMX got quite warm and did not react in any way. The 3.3V SMPS was burning hot.
?
I replaced the SMPS'es by the ones borrowed from my QMX+. Everything works, but no output power. The hardware test shows 1.0 SWR and 0.0W output power on all bands. Of course all filter and swr sweeps fail when there is no output.
What to do next? Is it enough to replace the PA transistors?
?
I feel that the QMX should have some protection against such short power inerrupts.
This is very important. As the SMPS voltages are controlled only at 1ms intervals, it is clear that the design relies on the assumption that no millisecond-scale power failures can occur.?
?
Could it be as simple as adding a suitable large electrolytic capacitor to the pins of the 12V power input jack?
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73
Matti OH6BEX
