Matti,
Very unfortunate problems you are having. The voltages you measured with the button pressed show that you have something shorting in your QMX+, on both the Vcc and Vdd lines.? It is not easy to say exactly what is shorted without further measurements, but most commonly there are issues with connections and solder flakes.? Or something external.??
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And if you shorted your Vdd to Vcc while probing, if you didn't have a current limit of 250mA or less set on your power supply, you likely blew one of the protection diodes, probably D109.?
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But it is not accurate nor fair to blame these issues on the QMX+ v2 or v3 SMPS design. Shorting without a fuse or current limit would damage some component in almost any design, yes, even with linear regulators.
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Perhaps QMX+ should have been designed with a 250mA fuse on the Vdd line, then assembly or handing issues that cause shorts would blow the fuse rather than the protection diode - then instead of placing blame on a power supply design,? ?we would be looking for what is shorting and fix it.
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Also note that a double long-press of the power button shouldn't have caused any issue.? I have done that before without consequences. Similar with a very long press, which first powers down then powers back up.
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Stan KC7XE?
