> My question regards the wiring on the input jack.  It has only two
> wires soldered to it and one is ground (center pin 2).  Can a MIDI
> system function with just the ground and the 'signal' input on pin 4
> but without a 'sink' or 'current source' connection on pin 5?

There must indeed be a return connection on pin 4.  The connector pins
are numbered, going around the semicircle, as 1 4 2 5 3.  MIDI is a
current-loop standard, meaning there must be a complete circuit.  The
center ground pin is used only for the shield, if the cable has one.

Your MIDI cable, and whatever MIDI source you are using to drive the
organ with, should be outputting the signals on pins 4 and 5.  If you
are using a non-standard source (say, supplied by the organ maker),
then be aware that "proper" MIDI cables connect the ground or shield at
one end only.  That could be why you aren't getting anything.

Mike Knudsen

 [ The MIDI cable is polarity sensitive.  Pin 4 goes to pin 4, pin 5
 [ connects to pin 5.  Pin 2 (center) may be connected to an optional
 [ cable shield at the sending end.  Pins 1 and 3 are not connected.
 [ -- Robbie