tim77777:
I can't measure 5mA. There seems to be much less than that.
I'm not fully up on the MIDI protocol, but I seem to remember something about a timing signal [might only be sent by a sequencer] but when you measure this current, perhaps the signal is transitioning, presumably between 5mA and 0mA. If it's mostly 0mA, with periodic transitions, that might explain your insufficient current reading.