On Tue, Jul 2, 2024 at 11:23 AM, Chris wrote:
3.9V.? This is reduced by the diode drop across D103, however D103 has a much higher current through it, maybe 100mA so will have a higher voltage drop, maybe 0.8V which gives a VDD of 3.1V.
Mark, I think Chris is right. So VDD = 3.01V is consistent and enough to run the controller.
then the measured voltages would be off by ?a factor of 3.3/3.1
I think, you are also right calculating this factor.
But the calculated Duty max don't fit to 8.1 V shown supply voltage. Testing my QMX (FW 018) I get the shown Duty max from 7.4 V. (Afaik Duty max is calculated from the supply voltage.) 7.4 V is close to your real input. So it looks like the controller know something more. (Later I will check something.)
The 3V3 voltage shown by Diagnostics should be the one from the output of the SMPS. I guess it's calculated from the signal ADC_3V3. In state of "Linear" (LIN_REG_EN = HIGH) the SMPS output is separated from VDD by Q111. The SMPS is working toward the artificial load R114 (47 ohm).
Following Diagnostics the 3V3 Duty cycle 49% is equal to Duty max. This means you have 3V3 SMPS overload with the result of only VDD = 2.54V. The question is the place of this overload. If Q111 is working well the overload should exist on the SMPS board. And I guess Q111 is working well because the VDD rail has 3.01V.
I would test the SMPS board using the off line method (see the link in the QRP Labs Wiki document
QMX and QMX+ Internal power supply.
73. Ludwig
