To create the M900X fixture, take the 7404 chips out of an assembled M900X.

Create five LED inserts.  Each insert starts with an empty 14 pin machine socket.
Into pins 2-7 insert three 3mm LEDs, with the cathode toward pin 7.  Leave pin 1
blank.  Similarly, into pins 8-13, insert three LEDs, this time with the cathode 
toward pin 13.  Leave pin 14 blank.

On the flip (pin) side of the socket, solder one end of a 3.5" wire (wire wrap
wire works fine) to the fat part of pin 7, with the free end pointing toward 
pin 9.  Wrap the wire over fat part of pin 9, and then back and forth over 
the fat parts of pins 5, 11, 3, and 13.  Solder each connection, then trim 
the excess wire from pin 13.

Insert all five of the LED inserts in place of the 7404 chips.

Make a few inches of 34 pin IDE cable, and insert one end into the M900X test 
fixture.  The other end of this cable goes into the M900X under test.

Run the M900X test by turning comments on ("C"), then using spaces to step 
through the test.  An LED should light for every other step, and the comment
will identify which pin should be lit.  For the M900X, this lights gates A-F 
in turn on each of E1 through E5.  (E1 is rightmost, E5 is leftmost.)

The test always "passes", so don't use that as an indicator of anything.
When run full speed, all LEDs should appear lit.  The printing of rows of 
"p" will create a strange flashing effect, as it introduces a pause during 
terminal output, making a random LED be on longer and appear brighter.

    Vince