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Brian,
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Does sound like you know what you are doing.
You have a very weird set of symptoms.
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I'm having a hard time imagining how plugging in the USB cable makes it work if there is a solid ground connection from power supply into the QMX and if the power supply is at a 1.5A current limit.
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The node inside the QMX dropping from 9v to 3v is a mystery, would be good to investigate that further.
My best guess is that you were looking at the V_IN node.
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I'd operate the rig for awhile outside the case so it can be probed with a voltmeter when it fails.
First see if you have your power supply voltage between QMX GND and V_IN on the QMX.
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At power up with the power-on knob pushed, the PWR_ON node pulls the gates of the PFET's at Q103 and Q105 down close to ground,
allowing power to flow through them to the node +12V.? Check to see if you have your power supply voltage at +12V.
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You said:? "Current limit was set at 1.5A and no current when the left knob was pressed, until after I connected the USB cable."
That's just weird if you really have 9v from the power supply going into the QMX, and you can measure 9v between V_IN and GND
on the QMX board.? The STM32F processor on the QMX draws around 0.1 Amps from the 3.3v rail, and you would see some?
current draw from your lab supply when the processor is working.? Assuming this isn't a fault in the ground cabling somehow,
the only way the USB port can affect what happens on the rig is if the processor is working.
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Jerry, KE7ER
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On Sun, Jan 26, 2025 at 11:03 AM, Brien - KE7WB wrote:
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