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Joe,
It is most often not useful to try and supply external 3.3V VDD - because the most common failures of 3.3V supply would also make an external supply not work.
With QMX+ and over-voltage, here are the things to look at first:
1) Inspect (and test if you can) the input TVS diode D110, right next? to the power connector.? This diode can short with over-voltage, as it tries to protect QMX+.? If it is shorted, remove it, and see if all works again, if so, you should replace this diode so it can continue protection - but the QMX+ will work without it.
2) If you can, set your power supply to about 7V with a 250mA current limit (this allows voltage testing without risk of doing damage)
3) Measure the power supply current when:
?? a) Just plug in power connector with QMX+ off
?? b) while pressing QMX+ power-on button
?? c) after releasing QMX+ power-on button
If the current at c) is somewhere between 120mA and 220mA, it is likely that your 3.3V supply is working, and you can connect with the PuTTY terminal and use the built-in diagnostics (even if your display is not on).? Your 5V? VCC may be damaged
If the current at c) is near 0, but very high at b), one or more of your finals may be blown/shorting - based on your description of the failure while not transmitting, I don't think this will be the case.
If the current at c) is near 0 and the current at b) is high, the D109 in your 3.3V smps may be shorted.
There are also many other possible faults from over-voltage, for which we need to do various measurements.
?
See also the first few steps in this trouble-shooting guide on the wiki: /g/QRPLabs/wiki/39617
And read this startup process to understand what goes on during the various stages of turning QMX+ on: /g/QRPLabs/wiki/36878
With QMX+ r2 or r3, the 3.3V and 5V smps are built onto the board, but the test process at this link (which was written for separate smps boards), can give you insight in what to measure and test on you QMX+ smps: /g/QRPLabs/wiki/37128
Good luck, and let us know if you get some measurements you don't understand.
Stan KC7XE |
