Art,
I didn't see a definitive answer yet and I know Jack is super busy trying to sort out everyone's problems so I'll answer your question.? The pad in question is shown on the back side of the Teensy 3.6 (and other Teensy's as well) pinout card that came with it, as the VIN/VUSB jumper and it says to cut that jumper if using a battery charger OR external power.? The battery charger isn't relevant here, but external power is so the jumper MUST be cut.

Now for the reason which isn't readily apparent.

You are powering the Teensy 3.6 from the 5 volt regulator on the JackAl board.? If you have not cut the jumper and plug the USB cable in to re-program the Teensy (or for some other purpose like CAT control or other serial I/O from the USB port) you are also supplying a nominal 5 volts from the USB port to the Teensy.? The two voltages will most certainly not be exactly equal as they come from two different power sources and they WILL conflict with possible damage to the Teensy's on-board 3.3V regulator and other circuitry (I know, I destroyed one by doing this before I figured it out).

So, in this case if you don't cut the jumper, don't connect the USB cable with the JackAl powered up.? By the same token, if you follow PJRC's directions and cut the jumper, you will have to power the JackAl up to get the Teensy operating before you will be able to re-program it.?

If, like me, you sometimes forget these things then cut the jumper (recommended anyway) and just remember that you have to have the JackAl powered up to use the USB connection to program the Teensy 3.6 (or to communicate with it for any reason).

Jim Sheldon - W0EB

___________________________________________________________________________________________________
(Art Olson)

12:52pm ? #129??

Jack

I vaguely recall some discussion about cutting the 5 volt pad on the teensy. Is this still necessary or am I off target.?

?

Art N2AJO