A bit of a followup to closeout the initial problem.
- I was able to borrow a thermal camera and found that Q7 was showing "hot"
- Replaced Q7 and no powerup of 3.3V rail.
- Using thermal camera C4 on 3.3V output was shorted.??
- Replaced cap C4
- IC1 3.3V was replaced with a more name brand Texas Instruments equivalent.??
- Added reverse polarity diode from across the input/output of the IC1 3.3V regulator for cheap insurance.? This is a common recommendation in these types of LDO's if there is a significant of output holdup capacitance and the input voltage depletes faster and could have reverse current through the regulator causing destruction.? That would only happen in a power cycling scenario.? I was doing a lot of plugging and unplugging shortly before the funny smells and involuntary power-down, so I'm super speculating and doesn't hurt to add the diode for protection.
- Rewound transformer for 9V operation to reduce power dissipation stress.
The QDX is now up and working.? I wasn't looking for a project within a project and a few Mouser orders and many troubleshooting sessions.? Now to burn this thing in parked on WSPR for a while.
Scott, kx9rt
