@pgoergen thanks for validating this!
As an explanation what could be going on: the Trusted Builder might have built this SEQ v4+ “to specs” of the original customer - i am not 100% sure, but i think it is possible (Andy knows better!) to wire the BLM Input (which is IN4 internally) to the separate MIDI IN4 port and take its signal away from the BLM port.
This is possible to allow users not wanting to use a MatriX to have a fourth MIDI IN, so if the original owner never intended to use a MatriX/BLM, this might have been a request to the builder.
If i remember correctly, in this case, just a single bridge must be moved over from the IN4 port to the BLM port.
Another more straightforward reason could be that IN4 itself is not working entirely correctly - i.e. the optocoupler (it is a single 8-pin IC that is swappable) might not work or might not be installed properly.
Both possible reasons should be easily debuggable and fixable.
Have a good evening and sorry for the inconvenience!
Best regards,
Peter
