I updated the manual for TTKS today. There were two important changes based on observations during assembly of units.
The first observation was that the USB-B pins were susceptible to being bent and needed to be carefully aligned prior to insertion. While USB-B is a nice durable connector, I will be thinking hard about it in future projects. More on that in a separate post about how people want specific applications, not general purpose widgets.
The second change was moving the BC517 insertion to a later point. The BC517 uses an annoying triangular foot print which does not match how the transistor comes from the factory. This requires bending the pins and then fussing with them to get them to go in. The net result is that the transistor won’t go in all the way and every board is a little different in terms of how far you can get the transistor in. Push too hard and you’ll collapse the pins. When it is inserted early in the process it is subject to stress during assembly.
Thus the simple solution is to leave the BC517 to last. This allows it to be protected by the relay which on average sits higher than the BC517.