I have just been through this with my 20m QCX.? Turns out IC3 had failed (probably after the 5V regulator failed). Even after I replaced the regulator and IC3 (I used a socket this time) it still didn't work. But I noticed that Q1 was hot even on receive.? Replacing this (again) brought the TX back to life.
It is worth checking that you don't have short from the centre pin to earth. And also that you have continuity from the antenna to C29 to show the LPF is not open circuit.
I would check the voltages on the pins of IC3 - I listed mine (key up and key down) in another thread. When my IC3 failed I still had receive audio but at much reduced volume, although the sidetone was still normal. Hot Q1, Q2 or Q3 on receive might indicate failure.
Steve G0KYA
