I’ve been tripped up several times now with my 4SQRP T41 because of the extended headers used to construct the Teensy/Audio Adapter stack. The thin stamped header pins, similar to those on the left in the picture below from the AI6YM v12 T41 kit, don’t always make good contact, leading to hard to trace problems with the T41. I believe the same type of header pins are specified in the v12 T41 BOM.
These problems usually arise after the Teensy stack has been removed and reinstalled in the T41. I did this recently when I redid the wiring for my 4SQRP T41 USB hub. Because I was working on transmit power calibration and had my T41 connected to a dummy load at the time, I didn’t notice that I had lost receive capability. I finally noticed when the frequency spectrum didn’t appear as I was trying to track down some calibration inconsistencies.
By this point I didn’t think of the removal/replacement of the Teensy as a cause of the problem. I spent a morning debugging, both hardware and software, which isn’t pleasant on the Teensy. Finally, after I determined that everything was ok up to the Main board, it dawned on me that I was probably having connectivity problems with the Teensy. For me, reseating the Teensy usually solves this type of problem and it did so in this case.
This problem has been reported by others. The best solution is to not use the stamped pin headers in the first place. Alternatives exist to create the Teensy/Audio adapter stack. The double insulated header in the center of the image above is a good option for the DIYer. For those that don’t want to bother building one themselves, ProtoSupplies will create a custom stack, as the one to the right in the image. That’s what I’ve used for testing in my v12 kit. I shouldn’t have any connectivity problems with that radio.