This is a classic presentation for a marginal power supply upstream of both units.? Will (WD5GJA/SK) and I saw a similar problem with a Radio Shack TRS-80 and a big HVAC fan at his house, many years ago.? His solution was to put a salvaged monster power filter in line ahead of the TRS-80.

When you key the transmitter, it keys the PA.? When the PA keys, assuming a 12V supply, it immediately draws somewhere between, oh, probably 4.5 amps to 8 amps.? If the power supply can't handle that sharp an edge on the current demand, the supply's output voltage WILL sag, and it can easily sag enough to drop the processor out.

The "throw money at it" solution is independent power supplies, ideally on different legs of the house feed.? Alternatively, you could find or design a suitable filter.

Good luck!

--John R. Strohm WB5YOO ?

On Fri, 27 Oct 2023 05:40:22 -0700, "Eric Fox via groups.io" <ericfox16@...> wrote:

Old Post, but related to my new problem.
My 50w PA has been working fine on 80m with my QCX+, but while in use recently, it began to have a distorted sound, heard via the sidetone, and then the QCX+ would reset whenever the CW key made contact.?? I've had the PA on the bench feeding it from signal generator and keying with QCX-mini.? I get power out, but I have signal (using O'scope) on both sides of several inductors meant to keep RF off the Bias network.? It is a reduced signal, but I don't think I should see any, or is this normal.??? If it is not correct to see any signal on transmit on the Bias Network side of these inductors, can a failed final transistor be a cause?? Is there another component failure others have seen that would cause this? ??

Thank you
Eric