Some weeks ago I found that a stream of wrong, malformed, spurious MIDI messages  was coming from the serial MIDI IN (the 5 pin MIDI in) , when used with a connected Keyboard.

After further investigation and lot of useful suggestion from the Teensy forum (https://forum.pjrc.com/threads/54891-MIDI-serial-(DIN)-to-usbMIDI-issues-got-weird-MIDI-messages?p=202167#post202167) I foud that the components and the wiring I used for the MIDI IN interface were wrong: I wired the 6N139 optocpupler (this is the only piece that's ok) but using the schematic for a different (obsolete) optocoupler.

So I had to open the Commander, remove the the main board (where are the MIDI interfaces too) and change the optocoupler's surrounding components.

Thanks to the modular design I adopted it was a fairly easily task and in a few hours I was able to put in again the main board.

Now I have a really steady stream of messages from MIDI IN: a must for a reliable instrument that has to be gig-worthy

---

I uploaded the correct schematic, that was also changed to show all the connector used and how I divided the boards.

The schematic source (KiCAD) is now under version control tto at the GitHub repository