PK232 will not TX rig

[G1ITV]

Hi All,
My fully upgraded PK232MBX has suddenly stopped tx'ing the rig (I have tried a few). All other operations are OK and working. I can key the rig by the microphone and this will tx' the rtty etc. I have re-made and tested the leads which are OK.
On veiwing the circuit diag I think the problem is in the two transistors (Q6 and Q4) or the IC (SN7406N).
Am I "Barking up the wrong Tree?", has anyone had this problem.
Any help appreciated before I purchase the components and dive in with a "Hot" iron.

Thanks'   Ken G1ITV

[G1ITV]

Hi All,
Thanks to the 2 hams who suggested "Q5". That was the problem.......

Ken G1ITV

[NT9E]

There is a test function on the PK-232 so that you can check your PTT line. There is also a command that if set will not key the ptt line as well. Have these 2 things been checked?