Re: QCX 40 has zero audio output

Skip Davis

I agree with Jim’s assessment about the open PCB trace. Robert have you measured from pin8 to ground on IC10 to see if there is a short? If no short is measured then that is a good sign. Then measured between pin8 of IC10 to the cathode of D3 there should be continuity (zero ohms). All B+ power goes through D3 and is distributed from this point to the 5vdc regulator, TX, and RX circuits. There is a small via trace that is on the bottom of the board the “dog-legs under the power block that maybe open. This trace connects to the three pin DVM/RF Probe first then to the rest of the RX audio circuits. The pin nearest the power input connector is 13.8vdc or what ever your voltage is your using to power the QCX minus about .4v drop across the diode.
I just finished repairing Jordan’s KN4SKY QCX and found this trace was burned open right at the solder pad for the diode. I guess it acted like an unintended fuse for the RX circuits.
I hope this helps you out.

Skip Davis NC9O

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