Hi Tom,
First, it is not a good idea to power the uBitx through the USB connector on the back of the radio.? That would be back-feeding the power through the 5-volt regulator on the Raduino board.? That can damage the regulator and ultimately cause it to fail and apply the full 12 volts to the Nano.
From what you have described, I would suspect that the power from the nearby transmitter damaged Q90.? Check to see if you have a short to ground on the base of Q90.? The alternative is to test following the directions on this spreadsheet from VU2ZAP:
/g/BITX20/files/VU2ZAPThe V6 and V4 have similar circuits for the transmitter, so the V4 measurements are good.
73
Evan
AC9TU
