Oh, lucky you! Then it's NOT the ADC problem. Just to be sure, it doesn't work if it's in the stand but it does work if you directly connect the standby input on the unit with the outer shell, right?
Then you have that problem, where the connection in the cradle is loose. I think there was a post from dreamcat4 on that issue. You need to open the stand and fix that connection.
I think I narrowed down my problem: I took the standby (PORT1) wire and directly held it to the tip -> standby. Then pressed it against the metal ring at the end of the handpiece, which makes contact with the stand and where the tip inserts -> No reaction.
Looked at it, thought: Hold on, when I insert the tip, these two metal bodies should make contact, thus it shouldn't matter which part connects..? Right, if I bend the inserted tip ever so slightly, it does put the unit into standby. So, there is actually a tiny circular gap between my tips and the handpiece which keeps them from making contact.. How the heck did that happen and how the heck do I fix it?
Regarding the stand: In my version of the T3A, the stand is simply a solid piece of metal with a round plug in the back for the standby wire, so when that is plugged in, the whole stand is connected. Also tried it with the stand connected, put the iron in the stand -> No reaction. Bend the tip a bit -> into standby it goes.. JFC
Thanks for all your help!